VegeWorx Plant Index - Letter S
- S-curve Threeawn - Aristida Ramosissima Engelm. ex A. Gray
- Saba - Saba (pichon) Pichon
- Sabaigrass - Eulaliopsis Binata (Retz.) C.E. Hubb.
- Sabaigrass - Eulaliopsis Honda
- Sabal Adansonii Guersent
- Sabal Bermudiana L.H. Bailey, orth. var.
- Sabal Deeringiana Small
- Sabal Exul (O.F. Cook) L.H. Bailey
- Sabal Glabra Sarg., non Mill.
- Sabal Jamesiana Small
- Sabal Louisiana (Darby) Bomhard
- Sabal Miamiensis Zona
- Sabal Texana (O.F. Cook) Becc.
- Sabal ×texensis Lockett & Read, nom. inval.
- Sabatia Alainii Vict.
- Sabatia Boykinii A. Gray
- Sabatia Campanulata (L.) Torr. var. gracilis (Michx.) Fernald
- Sabatia Campanulata (L.) Torr. var. grandiflora (A. Gray) S.F. Blake
- Sabatia Carnosa Small
- Sabatia Chloroides (Michx.) Pursh
- Sabatia Corymbosa Baldw.
- Sabatia Cubensis (Griseb.) Urb.
- Sabatia Decandra (Walter) Harper
- Sabatia Dodecandra (L.) Britton, Sterns & Poggenb. var. coriacea (Elliott) H.E. Ahl
- Sabatia Dodecandra (L.) Britton, Sterns & Poggenb. var. kennedyana (Fernald) H.E. A
- Sabatia Elliottii Steud.
- Sabatia Foliosa Fernald
- Sabatia Gracilis (Michx.) Salisb.
- Sabatia Gracilis (Michx.) Salisb. var. cubensis Griseb.
- Sabatia Gracilis (Michx.) Salisb. var. grandiflora A. Gray
- Sabatia Harperi Small
- Sabatia Lanceolata (Walter) Torr. & A. Gray
- Sabatia Maculata (Benth.) Benth. & Hook. f.
- Sabatia Obtusata S.F. Blake
- Sabatia Palmeri A. Gray
- Sabatia Paniculata (Michx.) Pursh
- Sabatia Paniculata auct. non (Michx.) Pursh
- Sabatia Purpusii Brandegee
- Sabatia Recurvans Small
- Sabatia Simulata Britton
- Saber Bogmat - Wolffiella Oblonga (Phil.) Hegelm.
- Sabicea Hirsuta Kunth
- Sabin's Lupine - Lupinus Sabinianus Douglas ex Lindl.
- Sabina Californica (Carrière) Antoine
- Sabina Flaccida (Schltdl.) Antoine
- Sabina Horizontalis (Moench) Rydb.
- Sabina Monosperma (Engelm.) Rydb.
- Sabina Occidentalis (Hook.) A. Heller
- Sabina Osteosperma (Torr.) Antoine
- Sabina Prostrata (Pers.) Antoine
- Sabina Scopulorum (Sarg.) Rydb.
- Sabina Silicicola Small
- Sabina Utahensis (Engelm.) Rydb.
- Sabina Virginiana (L.) Antoine
- Sabinal Prairie Clover - Dalea Sabinalis (S. Watson) Shinners
- Sabine Buttercup - Ranunculus Sabinei R. Br.
- Sabine River Wakerobin - Trillium Gracile J.D. Freeman
- Sabinea Florida (Vahl) DC.
- Sabinea Punicea Urb.
- Sabinon - Croton Poecilanthus Urb.
- Sabulina Brevifolia (Nutt. ex Torr. & A. Gray) Small
- Sabulina Caroliniana (Walter) Small
- Sabulina Glabra (Michx.) Small
- Sabulina Groenlandica (Retz.) Small
- Sabulina Patula (Michx.) Small
- Sabulina Stricta (Michx.) Small
- Sabulina Uniflora (Walter) Small
- Sabulina Uniflora auct. non (Walter) Small
- Sacahuista - Nolina Microcarpa S. Watson
- Sacajawea Bitter Root - Lewisia Sacajaweana B.L. Wilson & E. Rey-Vizg.
- Sacapellote - Acourtia Microcephala DC.
- Sacatrapo - Caperonia Palustris (L.) A. St.-Hil.
- Saccharodendron Barbatum (Michx.) Nieuwl.
- Saccharodendron Floridanum (Chapm.) Nieuwl.
- Saccharodendron Grandidentatum (Nutt.) Nieuwl.
- Saccharodendron Leucoderme (Small) Nieuwl.
- Saccharodendron Nigrum (Michx. f.) Small
- Saccharodendron Saccharum (Marshall) Moldenke
- Saccharum Alopecuroideum (L.) Nutt., orth. var.
- Saccharum Alopecuroidum (L.) Nutt., database artifact
- Saccharum Arundinaceum Retz. [excluded]
- Saccharum Barberi Jeswiet [excluded]
- Saccharum Biflorum Forssk.
- Saccharum Ciliare Andersson
- Saccharum Contortum (Elliott) Nutt.
- Saccharum Contractum Kunth
- Saccharum Pappiferum Lam.
- Saccharum Repens Willd.
- Saccharum Sagittatum Aubl.
- Saccharum Sinense Roxb. [excluded]
- Saccharum Strictum (Elliott) Elliott ex Nutt.
- Sacciolepis Myosuroides (R. Br.) A. Camus
- Sacciolepis Myuros (Lam.) Chase
- Saccomorpha Hyporhoda (Th. Fr.) Clauzade & Roux
- Saccomorpha Icmalea (Ach.) Clauzade & Roux
- Saccomorpha Oligotropha (J.R. Laundon) Clauzade & Roux
- Saccomorpha Uliginosa (Schrad.) Hafellner
- Sachet's Starviolet - Hedyotis Sachetiana Fosberg
- Sachsia Bahamensis Urb.
- Sachsia - Sachsia Griseb.
- Sack Saltbush - Atriplex Saccaria S. Watson
- Sacky Sac Bean - Inga Laurina (Sw.) Willd.
- Sacoila Lanceolata (Aubl.) Garay
- Sacoila Lanceolata (Aubl.) Garay var. luteoalba (Rchb. f.) Sauleda, Wunderlin & B.F
- Sacoila Lanceolata (Aubl.) Garay var. paludicola (Luer) Sauleda, Wunderlin & B.F. H
- Sacolia Squamulosa (Kunth) Garay
- Sacramento Burbark - Triumfetta Semitriloba Jacq.
- Sacramento Cryptantha - Cryptantha Crinita Greene
- Sacramento Mesamint - Pogogyne Ziziphoroides Benth.
- Sacramento Mountain Foxtail Cactus - Escobaria Villardii Castetter, Pierce & Schwerin
- Sacramento Mountain Indian Paintbrush - Castilleja Wootonii Standl.
- Sacramento Mountain Thistle - Cirsium Vinaceum Wooton & Standl.
- Sacramento Orcutt Grass - Orcuttia Viscida (Hoover) J. Reeder
- Sacramento Ragwort - Senecio Sacramentanus Wooton & Standl.
- Sacramento Saltbush - Atriplex Persistens Stutz & G.L. Chu
- Sacramento Valley Buttercup - Ranunculus Canus Benth.
- Sacramento Waxydogbane - Cycladenia Humilis Benth.
- Sacramento Waxydogbane - Cycladenia Humilis Benth. var. humilis
- Sacramento Waxydogbane - Cycladenia Humilis Benth. var. venusta (Eastw.) Woodson ex Munz
- Sacred Bamboo - Nandina Domestica Thunb.
- Sacred Garlic Pear - Crateva Religiosa G. Forst.
- Sacred Lotus - Nelumbo Nucifera Gaertn.
- Sacred Thorn-apple - Datura Wrightii Regel
- Saddle Mountain Bittercress - Cardamine Pattersonii L.F. Hend.
- Saddle Mountain Saxifrage - Saxifraga Hitchcockiana Elvander
- Saddlebush - Mortonia A. Gray
- Sadleria Hillebrandii W.J. Rob.
- Sadleria Polystichoides (Brack.) A. Heller
- Sadleria - Sadleria Kaulf.
- Sadleria Unisora (Baker) W.J. Rob.
- Saelania Moss - Saelania Glaucescens (Hedw.) Broth.
- Saelania Moss - Saelania Lindb.
- Safflower - Carthamus Tinctorius L.
- Safford's Lellingeria - Lellingeria Saffordii (Maxon) A.R. Sm. & R.C. Moran
- Saffron Plum - Sideroxylon Celastrinum (Kunth) T.D. Penn.
- Saffron Ragwort - Packera Crocata (Rydb.) W.A. Weber & Á. Löve
- Saffron-flowered Lupine - Lupinus Croceus Eastw.
- Saffron-flowered Lupine - Lupinus Croceus Eastw. var. croceus
- Saffron-flowered Lupine - Lupinus Croceus Eastw. var. pilosellus (Eastw.) Munz
- Sage - Salvia L.
- Sage - Salvia Patens Cav.
- Sage - Salvia ×bernardina Parish ex Greene (pro sp.)
- Sage - Salvia ×palmeri A. Gray (pro sp.)
- Sage - Salvia ×superba Stapf
- Sagebrush - Artemisia L.
- Sagebrush - Artemisia Rupestris L.
- Sagebrush Beardtongue - Penstemon Cyathophorus Rydb.
- Sagebrush Buttercup - Ranunculus Glaberrimus Hook.
- Sagebrush Buttercup - Ranunculus Glaberrimus Hook. var. glaberrimus
- Sagebrush Cholla - Grusonia Pulchella (Engelm.) H. Rob.
- Sagebrush Combseed - Pectocarya Linearis (Ruiz & Pav.) DC.
- Sagebrush Combseed - Pectocarya Linearis (Ruiz & Pav.) DC. ssp. ferocula (I.M. Johnst.) Thorne
- Sagebrush False Dandelion - Nothocalais Troximoides (A. Gray) Greene
- Sagebrush Fleabane - Erigeron Austiniae Greene
- Sagebrush Indian Paintbrush - Castilleja Lineariiloba (Benth.) T.I. Chuang & Heckard
- Sagebrush Mariposa Lily - Calochortus Macrocarpus Douglas
- Sagebrush Mariposa Lily - Calochortus Macrocarpus Douglas var. macrocarpus
- Sagebrush Phlox - Phlox Aculeata A. Nelson
- Sagebrush Rockcress - Arabis Cobrensis M.E. Jones
- Sagebrush Stickseed - Hackelia Diffusa (Lehm.) I.M. Johnst. var. arida (Piper) R.L. Carr
- Sagebrush Violet - Viola Vallicola A. Nelson
- Sagebrush Violet - Viola Vallicola A. Nelson var. vallicola
- Sagediopsis (sacc.) Vain.
- Sagediopsis Barbara (Th. Fr.) R. Sant. & Triebel
- Sagediopsis Campsteriana (Linds.) D. Hawksw. & R. Sant.
- Sageleaf Willow - Salix Candida Flueggé ex Willd.
- Sagina Apetala Ard. var. barbata Fenzl
- Sagina Crassicaulis S. Watson
- Sagina Crassicaulis S. Watson var. littoralis (Hultén) Hultén
- Sagina Decumbens (Elliott) Torr. & A. Gray var. smithii (A. Gray) S. Watson
- Sagina Fontinalis Short & Peter
- Sagina Hawaiensis Pax
- Sagina Intermedia Fenzl
- Sagina Linnaei C. Presl
- Sagina Littoralis Hultén
- Sagina Maxima A. Gray var. littorea (Mack.) H. Hara
- Sagina Micrantha (Bunge) Fernald
- Sagina Nivalis (Lindbl.) Fr. var. caespitosa (J. Vahl) B. Boivin
- Sagina Nodosa (L.) Fenzl var. borealis (Crow) Cronquist
- Sagina Nodosa (L.) Fenzl var. glandulosa (Besser) Asch.
- Sagina Nodosa (L.) Fenzl var. pubescens (Besser) Mert. & W.D.J. Koch
- Sagina Occidentalis S. Watson
- Sagina Procumbens L. var. compacta Lange
- Sagina Saginoides (L.) Karst. var. hesperia Fernald
- Sagina Virginica L.
- Sagina ×normaniana Lagerh.
- Sagiolechia Lichen - Sagiolechia A. Massal.
- Sagiolechia Lichen - Sagiolechia Protuberans (Ach.) A. Massal.
- Sagiolechia Lichen - Sagiolechia Rhexoblephara (Nyl.) Zahlbr.
- Sagittaria Angustifolia Lindl.
- Sagittaria Arifolia Nutt. ex J.G. Sm.
- Sagittaria Chapmanii (J.G. Sm.) C. Mohr
- Sagittaria Chinensis Pursh
- Sagittaria Cycloptera (J.G. Sm.) C. Mohr
- Sagittaria Eatonii J.G. Sm.
- Sagittaria Engelmanniana J.G. Sm. ssp. brevirostra (Mack. & Bush) Bogin
- Sagittaria Engelmanniana J.G. Sm. ssp. longirostra (Micheli) Bogin
- Sagittaria Engelmanniana J.G. Sm. ssp. longirostra auct. non Micheli
- Sagittaria Esculenta Howell
- Sagittaria Falcata Pursh
- Sagittaria Graminea Michx. ssp. chapmanii (J.G. Sm.) Haynes & C.B. Hellquist
- Sagittaria Graminea Michx. ssp. weatherbiana (Fernald) Haynes & C.B. Hellquist
- Sagittaria Graminea Michx. var. cristata (Engelm.) Bogin
- Sagittaria Graminea Michx. var. macrocarpa (J.G. Sm.) Bogin
- Sagittaria Graminea Michx. var. platyphylla Engelm.
- Sagittaria Graminea Michx. var. teres (S. Watson) Bogin
- Sagittaria Greggii J.G. Sm.
- Sagittaria Lancifolia L. var. media Micheli
- Sagittaria Latifolia Willd. var. obtusa (Muhl. ex Willd.) Wiegand
- Sagittaria Latifolia Willd. var. pubescens (Muhl. ex Nutt.) J.G. Sm.
- Sagittaria Longirostra (Micheli) J.G. Sm.
- Sagittaria Longirostra (Micheli) J.G. Sm. var. australis J.G. Sm.
- Sagittaria Longirostra auct. non (Micheli) J.G. Sm.
- Sagittaria Lorata (Chapm.) Small
- Sagittaria Macrocarpa J.G. Sm.
- Sagittaria Mohrii J.G. Sm.
- Sagittaria Montevidensis Cham. & Schltdl. ssp. calycina (Engelm.) Bogin
- Sagittaria Montevidensis Cham. & Schltdl. ssp. spongiosa (Engelm.) Bogin
- Sagittaria Montevidensis Cham. & Schltdl. var. spongiosa (Engelm.) B. Boivin
- Sagittaria Obtusa Muhl. ex Willd., non Thunb.
- Sagittaria Ornithorhyncha Small
- Sagittaria Planipes Fernald
- Sagittaria Pubescens Muhl. ex Nutt.
- Sagittaria Spathulata (J.G. Sm.) Buchenau
- Sagittaria Stagnorum Small
- Sagittaria Subulata (L.) Buchenau var. gracillima (S. Watson) J.G. Sm.
- Sagittaria Subulata (L.) Buchenau var. kurziana (Glück) Bogin
- Sagittaria Subulata (L.) Buchenau var. natans (Michx.) J.G. Sm.
- Sagittaria Subulata (L.) Buchenau var. subulata
- Sagittaria Variabilis Engelm. var. obtusa (Muhl. ex Willd.) Engelm.
- Sagittaria Viscosa C. Mohr
- Sagittaria Weatherbiana Fernald
- Sago Palm - Cycas Revoluta Thunb.
- Sago Palm - Metroxylon Sagu Rottb.
- Sago Pondweed - Stuckenia Pectinata (L.) Börner
- Sagotia Triflora (L.) Duchass. & Walp.
- Saguaro - Carnegiea Britton & Rose
- Saguaro - Carnegiea Gigantea (Engelm.) Britton & Rose
- Sainfoin - Onobrychis Mill.
- Sainfoin - Onobrychis Viciifolia Scop.
- Saint-cyr Iris - Iris ×sancti-cyrii Rouss.
- Saintedwood - Ternstroemia Heptasepala Krug & Urb.
- Saints Fleabane - Erigeron Sanctarum S. Watson
- Sakaki - Cleyera Japonica Thunb.
- Sakhalin Corktree - Phellodendron Sachalinense (F. Schmidt) Sarg.
- Sakhalin Spruce - Picea Glehnii (F. Schmidt) Mast.
- Sal Tree - Shorea Robusta C.F. Gaertn.
- Salac Palm - Salacca Edulis Reinw.
- Salacca - Salacca Reinw.
- Salacia Chinensis L.
- Salacia L.
- Salad Violet - Viola ×esculenta Elliott (pro sp.)
- Salal - Gaultheria Shallon Pursh
- Salicornia Ambigua Michx.
- Salicornia Europaea L. ssp. rubra (A. Nelson) Breitung
- Salicornia Europaea L. var. pachystachya (W.D.J. Koch) Fernald
- Salicornia Europaea L. var. prona (Lunell) B. Boivin
- Salicornia Europaea L. var. prostrata auct. non (Pall.) Fernald
- Salicornia Europaea L. var. simplex (Pursh) Fernald
- Salicornia Europaea auct. non L.
- Salicornia Europaea sensu Wolff & Jefferies, non L.
- Salicornia Fruticosa (L.) L.
- Salicornia Herbacea auct. non (L.) L.
- Salicornia Maritima auct. non Wolff & Jefferies
- Salicornia Mucronata Bigelow, non Lag.
- Salicornia Pacifica Standl.
- Salicornia Perennis Mill.
- Salicornia Prostrata auct. non Pall.
- Salicornia Ramosissima auct. non J. Woods
- Salicornia Subterminalis Parish
- Salicornia Utahensis Tidestr.
- Salicornia Virginica L.
- Salina Wildrye - Leymus Salinus (M.E. Jones) Á. Löve
- Salina Wildrye - Leymus Salinus (M.E. Jones) Á. Löve ssp. salinus
- Salinas Milkvetch - Astragalus Macrodon (Hook. & Arn.) A. Gray
- Salinas River Tarweed - Deinandra Pentactis (D.D. Keck) B.G. Baldw.
- Salinas Valley Goldfields - Lasthenia Leptalea (A. Gray) Ornduff
- Salinas Valley Popcornflower - Plagiobothrys Uncinatus J.T. Howell
- Saline Phlox - Phlox Kelseyi Britton ssp. salina (M.E. Jones) Wherry
- Saline Saltbush - Atriplex Subspicata (Nutt.) Rydb.
- Saline Valley Phacelia - Phacelia Amabilis Constance
- Salix Acutidens Rydb.
- Salix Acutifolia auct. non Hook.
- Salix Adenophylla Hook.
- Salix Aegyptiaca L.
- Salix Alaxensis (Andersson) Coville ssp. longistylis (Rydb.) Hultén
- Salix Alaxensis (Andersson) Coville var. obovalifolia C.R. Ball
- Salix Alaxensis (Andersson) Coville var. silicicola (Raup) B. Boivin
- Salix Alba L. ssp. caerulea (Sm.) Rech. f.
- Salix Alba L. ssp. vitellina (L.) Arcang.
- Salix Alba L. var. caerulea (Sm.) Sm.
- Salix Alba L. var. calva G. Mey.
- Salix Alba L. var. vitellina (L.) Stokes
- Salix Albertana Rowlee
- Salix Aliena Flod.
- Salix Alpestris Andersson var. americana Andersson
- Salix Alpina Walter
- Salix Ambigua Pursh, non Ehrh.
- Salix Amelanchieroides L. Kelso
- Salix Amphibia Small
- Salix Amplifolia Coville
- Salix Amygdaloides Andersson var. wrightii (Andersson) C.K. Schneid.
- Salix Anamesa C.K. Schneid.
- Salix Ancorifera Fernald
- Salix Anglorum Cham.
- Salix Anglorum Cham. var. antiplasta C.K. Schneid.
- Salix Anglorum Cham. var. araioclada C.K. Schneid.
- Salix Anglorum Cham. var. kophophylla C.K. Schneid.
- Salix Anglorum auct. non Cham.
- Salix Angustata Pursh
- Salix Apennina A.K. Skvortsov
- Salix Arbuscula L. var. labradorica (Andersson) Andersson
- Salix Arbusculoides Andersson var. glabra (Andersson) Andersson ex C.K. Schneid.
- Salix Arbutifolia auct. non Pall.
- Salix Arctica Liebm., non Pall.
- Salix Arctica Pall. ssp. crassijulis (Trautv.) Skvort.
- Salix Arctica Pall. ssp. petraea (Andersson) Á. Löve & D. Löve & Kapoor
- Salix Arctica Pall. ssp. tortulosa (Trautv.) Hultén
- Salix Arctica Pall. var. antiplasta (C.K. Schneid.) Fernald
- Salix Arctica Pall. var. araioclada (C.K. Schneid.) Raup
- Salix Arctica Pall. var. brownei Andersson
- Salix Arctica Pall. var. caespitosa (Kennedy) L. Kelso
- Salix Arctica Pall. var. graminifolia (E.H. Kelso) L. Kelso
- Salix Arctica Pall. var. kophophylla (C.K. Schneid.) Polunin
- Salix Arctica Pall. var. pallasii (Andersson) Kurtz
- Salix Arctica Pall. var. petraea (Andersson) Bebb
- Salix Arctica Pall. var. petrophila (Rydb.) L. Kelso
- Salix Arctica Pall. var. subcordata (Andersson) C.K. Schneid.
- Salix Arctica Pall. var. tortulosa (Trautv.) Raup
- Salix Arctica R. Br. ex Richardson, non Pall.
- Salix Arctolitoralis Hultén
- Salix Arctophila Cockerell ex A. Heller var. lejocarpa (Andersson) C.K. Schneid.
- Salix Argophylla Nutt.
- Salix Arguta Andersson
- Salix Arguta Andersson var. alpigena Andersson
- Salix Arguta Andersson var. erythrocoma (Andersson) Andersson
- Salix Arguta Andersson var. hirtisquama (Andersson) Andersson
- Salix Arguta Andersson var. lasiandra (Benth.) Andersson
- Salix Arguta Andersson var. pallescens Andersson
- Salix Argyrocarpa Andersson var. denudata Andersson
- Salix Astatulana Murrill & Palmer
- Salix Atra Rydb.
- Salix Austinae Bebb
- Salix Babylonica auct. non L.
- Salix Babylonica auct. non L.
- Salix Bakeri Seemen
- Salix Balsamifera (Hook.) Barratt ex Andersson
- Salix Balsamifera (Hook.) Barratt ex Andersson var. alpestris Bebb
- Salix Balsamifera (Hook.) Barratt ex Andersson var. lanceolata Bebb
- Salix Balsamifera (Hook.) Barratt ex Andersson var. vegeta Bebb
- Salix Barclayi Andersson var. angustifolia (Andersson) Andersson ex C.K. Schnei
- Salix Barclayi Andersson var. cochetopiana L. Kelso
- Salix Barclayi Andersson var. commutata (Bebb) L. Kelso
- Salix Barclayi Andersson var. conjuncta (Bebb) C.R. Ball ex C.K. Schneid.
- Salix Barclayi Andersson var. hebecarpa Andersson
- Salix Barclayi Andersson var. latiuscula Andersson
- Salix Barclayi Andersson var. neomexicana (E.H. Kelso) L. Kelso
- Salix Barclayi Andersson var. padophylla (Rydb.) L. Kelso
- Salix Barclayi Andersson var. pseudomonticola (C.R. Ball) L. Kelso
- Salix Barclayi Andersson var. resurrectionis L. Kelso
- Salix Barclayi Andersson var. uncompahgre L. Kelso
- Salix Barclayi Andersson var. veritomonticola L. Kelso
- Salix Barrattiana Hook. var. angustifolia Andersson
- Salix Barrattiana Hook. var. latifolia Andersson
- Salix Barrattiana Hook. var. marcescens Raup
- Salix Barrattiana Hook. var. tweedyi Bebb ex Rose
- Salix Bebbiana Sarg. var. capreifolia (Fernald) Fernald
- Salix Bebbiana Sarg. var. depilis Raup
- Salix Bebbiana Sarg. var. luxurians (Fernald) Fernald
- Salix Bebbiana Sarg. var. perrostrata (Rydb.) C.K. Schneid.
- Salix Bebbiana Sarg. var. projecta (Fernald) C.K. Schneid.
- Salix Behringica Seemen
- Salix Bella Piper
- Salix Bigelovii Torr.
- Salix Blanda Andersson, database artifact
- Salix Bockii Seemen
- Salix Boiseana A. Nelson
- Salix Bolanderiana Rowlee
- Salix Bonplandiana Kunth var. laevigata (Bebb) Dorn
- Salix Bonplandiana Kunth var. toumeyi (Britton & Shafer) C.K. Schneid.
- Salix Brachycarpa Nutt. ssp. brachycarpa
- Salix Brachycarpa Nutt. ssp. fullertonensis (C.K. Schneid.) Á. Löve & D. Löve
- Salix Brachycarpa Nutt. ssp. niphoclada (Rydb.) Argus
- Salix Brachycarpa Nutt. var. alticola E.H. Kelso
- Salix Brachycarpa Nutt. var. antimima (C.K. Schneid.) Raup
- Salix Brachycarpa Nutt. var. fullertonensis (C.K. Schneid.) Argus
- Salix Brachycarpa Nutt. var. glabellicarpa C.K. Schneid.
- Salix Brachycarpa Nutt. var. mexiae C.R. Ball
- Salix Brachycarpa Nutt. var. sansonii C.R. Ball
- Salix Brachystachys Benth.
- Salix Brachystachys Benth. var. scouleriana (Barratt ex Hook.) Andersson
- Salix Breweri Bebb var. delnortensis (C.K. Schneid.) Jeps.
- Salix Brownei (Andersson) Bebb
- Salix Brownei (Andersson) Bebb var. petraea (Andersson) Bebb
- Salix Brownii (Andersson) Bebb var. tenera (Andersson) M.E. Jones
- Salix Caespitosa Kennedy
- Salix Calcicola Fernald & Wiegand var. glandulosior B. Boivin
- Salix Calcicola Fernald & Wiegand var. nicholsiana Polunin
- Salix Californica Bebb
- Salix Callicarpaea Trautv.
- Salix Candida Flueggé ex Willd. var. denudata Andersson
- Salix Candida Flueggé ex Willd. var. tomentosa Andersson
- Salix Candidula Nieuwl.
- Salix Capreoides Andersson
- Salix Cascadensis Cockerell var. thompsonii Brayshaw
- Salix Caudata (Nutt.) A. Heller
- Salix Caudata (Nutt.) A. Heller var. bryantiana C.R. Ball & Braceline
- Salix Caudata (Nutt.) A. Heller var. parvifolia C.R. Ball
- Salix Chapmanii Small
- Salix Chilensis Molina
- Salix Chlorolepis Fernald var. antimima C.K. Schneid.
- Salix Chlorophylla Andersson
- Salix Chlorophylla Andersson var. monica (Bebb) Flod.
- Salix Chlorophylla Andersson var. nelsonii (C.R. Ball) Flod.
- Salix Chlorophylla Andersson var. pellita (Andersson) Andersson
- Salix Chlorophylla Andersson var. pychnocarpa (Andersson) Andersson
- Salix Cinerea L. ssp. atrocinerea (Brot.) Guinier
- Salix Cinerea L. ssp. cinerea
- Salix Cinerea L. ssp. oleifolia (Sm.) Macreight
- Salix Coactilis Fernald
- Salix Columbiana (Dorn) Argus
- Salix Commutata Bebb var. denudata Bebb
- Salix Commutata Bebb var. mixta Piper
- Salix Commutata Bebb var. puberula Bebb
- Salix Commutata Bebb var. rubicunda Jeps.
- Salix Commutata Bebb var. sericea Bebb
- Salix Conformis Forbes
- Salix Congesta (Bebb ex Rothr.) J.T. Howell
- Salix Conifera Muhl., non Wangenh.
- Salix Conjuncta Bebb
- Salix Cordata Michx. var. abrasa Fernald
- Salix Cordata Michx. var. crux-aureae L. Kelso
- Salix Cordata Michx. var. denveriana L. Kelso
- Salix Cordata Michx. var. desolata (E.H. Kelso) L. Kelso
- Salix Cordata Michx. var. ligulifolia (C.R. Ball) L. Kelso
- Salix Cordata Michx. var. monticola (Bebb) L. Kelso
- Salix Cordata Michx. var. platyphylla (C.R. Ball) L. Kelso
- Salix Cordata Michx. var. rigida (Muhl.) B. Boivin
- Salix Cordata Muhl. ssp. rigida (Muhl.) Andersson
- Salix Cordata Muhl. var. angustata (Pursh) Andersson
- Salix Cordata Muhl. var. balsamifera Hook.
- Salix Cordata Muhl. var. glaucophylla Bebb
- Salix Cordata Muhl. var. lutea (Nutt.) Bebb
- Salix Cordata Muhl. var. mackenzieana Hook.
- Salix Cordata Muhl. var. missouriensis (Bebb) Mack. & Bush
- Salix Cordata Muhl. var. myricoides (Muhl.) Carey
- Salix Cordata Muhl. var. rigida (Muhl.) Andersson, nom. illeg.
- Salix Cordata Muhl. var. rigida (Muhl.) Carey
- Salix Cordata Muhl. var. vestita (Andersson) Bebb, nom. dub.
- Salix Cordata Muhl. var. watsonii Bebb
- Salix Cordata Muhl., non Michx., nom. illeg.
- Salix Cordifolia Pursh
- Salix Cordifolia Pursh ssp. callicarpaea (Trautv.) Á. Löve
- Salix Cordifolia Pursh var. callicarpaea (Trautv.) Fernald
- Salix Cordifolia Pursh var. eucycla Fernald
- Salix Cordifolia Pursh var. intonsa Fernald
- Salix Cordifolia Pursh var. macounii (Rydb.) C.K. Schneid.
- Salix Cordifolia Pursh var. tonsa Fernald
- Salix Coulteri Andersson
- Salix Covillei Eastw.
- Salix Crassa Barratt
- Salix Crassijulis Trautv.
- Salix Cuneata Nutt.
- Salix Cuneata Turcz. ex Ledeb., non Nutt.
- Salix Curtiflora auct. non Andersson
- Salix Cutleri Tuck.
- Salix Cutleri Tuck. var. labradorica (Andersson) Andersson
- Salix Cyclophylla Rydb.
- Salix Denudata Raf.
- Salix Depressa L. ssp. rostrata (Richardson) Hiitonen
- Salix Desertorum Richardson
- Salix Desertorum Richardson var. elata Andersson
- Salix Desertorum Richardson var. fruticulosa Andersson
- Salix Desertorum Richardson var. stricta Andersson
- Salix Discolor Muhl. var. eriocephala (Michx.) Andersson
- Salix Discolor Muhl. var. latifolia Andersson
- Salix Discolor Muhl. var. overi C.R. Ball
- Salix Discolor Muhl. var. prinoides (Pursh) Andersson
- Salix Discolor Muhl. var. rigidior (Andersson) C.K. Schneid.
- Salix Dissymetrica L. Kelso
- Salix Dodgeana Rydb.
- Salix Dodgeana Rydb. var. subrariflora (L. Kelso) L. Kelso
- Salix Drummondiana Barratt ex Hook. ssp. subcaerulea (Piper) A.E. Murray
- Salix Drummondiana Barratt ex Hook. var. bella (Piper) C.R. Ball
- Salix Drummondiana Barratt ex Hook. var. subcaerulea (Piper) C.R. Ball
- Salix Dubia Trautv.
- Salix Elegantissima K. Koch
- Salix Eriocephala Michx. ssp. mackenzieana (Hook.) Dorn
- Salix Eriocephala Michx. var. famelica (C.R. Ball) Dorn
- Salix Eriocephala Michx. var. ligulifolia (C.R. Ball) Dorn
- Salix Eriocephala Michx. var. mackenzieana (Hook.) Dorn
- Salix Eriocephala Michx. var. monochroma (C.R. Ball) Dorn
- Salix Eriocephala Michx. var. watsonii (Bebb) Dorn
- Salix Excelsa S.G. Gmel.
- Salix Exigua Nutt. ssp. interior (Rowlee) Cronquist
- Salix Exigua Nutt. ssp. melanopsis (Nutt.) Cronquist
- Salix Exigua Nutt. var. angustissima (Andersson) Reveal & Broome
- Salix Exigua Nutt. var. columbiana Dorn
- Salix Exigua Nutt. var. exterior (Fernald) C.F. Reed
- Salix Exigua Nutt. var. gracilipes (C.R. Ball) Cronquist
- Salix Exigua Nutt. var. hindsiana (Benth.) Dorn
- Salix Exigua Nutt. var. luteosericea (Rydb.) C.K. Schneid.
- Salix Exigua Nutt. var. nevadensis (S. Watson) C.K. Schneid.
- Salix Exigua Nutt. var. parishiana (Rowlee) Jeps.
- Salix Exigua Nutt. var. pedicellata (Andersson) Cronquist
- Salix Exigua Nutt. var. sericans (Nees) Dorn
- Salix Exigua Nutt. var. sessilifolia (Nutt.) Dorn
- Salix Exigua Nutt. var. stenophylla (Rydb.) C.K. Schneid.
- Salix Exigua Nutt. var. tenerrima (L.F. Hend.) C.K. Schneid.
- Salix Exigua Nutt. var. virens Rowlee
- Salix Exigua auct. non. Nutt.
- Salix Exilifolia Dorn
- Salix Falcata Pursh
- Salix Fallax Raup
- Salix Famelica (C.R. Ball) Argus
- Salix Farriae C.R. Ball var. microserrulata C.R. Ball
- Salix Farriae C.R. Ball var. walpolei Coville & C.R. Ball
- Salix Fendleriana Andersson
- Salix Fernaldii Blank.
- Salix Flagellaris Hultén
- Salix Flava Rydb., non Schoepf
- Salix Flavescens Nutt.
- Salix Flavescens Nutt. var. capreoides (Andersson) Bebb
- Salix Flavescens Nutt. var. scouleriana (Barratt ex Hook.) Bebb
- Salix Flavovirens Hornem.
- Salix Fluviatilis Nutt. var. argophylla (Nutt.) Sarg.
- Salix Fluviatilis Nutt. var. sericans (Nees) B. Boivin
- Salix Fluviatilis Nutt. var. sessilifolia (Nutt.) Scoggan
- Salix Fluviatilis Nutt. var. tenerrima (L.F. Hend.) Howell
- Salix Fluviatilis Nutt., nom. utique rej.
- Salix Fluviatilis auct. non Nutt.
- Salix Franciscana Seemen
- Salix Fulcrata Andersson var. subglauca Andersson
- Salix Fullertonensis C.K. Schneid.
- Salix Fuscata Pursh
- Salix Fuscescens Andersson var. hebecarpa Fernald
- Salix Fuscescens Andersson var. reducta C.R. Ball
- Salix Geyeriana Andersson ssp. argentea (Bebb) A.E. Murray
- Salix Geyeriana Andersson var. argentea (Bebb) C.K. Schneid.
- Salix Geyeriana Andersson var. meleina J.K. Henry
- Salix Glabra Scop.
- Salix Glacialis Andersson
- Salix Glauca L. ssp. acutifolia (Hook.) Hultén
- Salix Glauca L. ssp. desertorum (Richardson) Hultén
- Salix Glauca L. ssp. glabrescens (Andersson) Hultén
- Salix Glauca L. ssp. orestera (C.K. Schneid.) Youngberg
- Salix Glauca L. var. alicea C.R. Ball
- Salix Glauca L. var. callicarpaea (Trautv.) Argus
- Salix Glauca L. var. glabrescens (Andersson) C.K. Schneid.
- Salix Glauca L. var. kenosha (L. Kelso) L. Kelso
- Salix Glauca L. var. macounii (Rydb.) B. Boivin
- Salix Glauca L. var. niphoclada (Rydb.) Wiggins
- Salix Glauca L. var. orestera (C.K. Schneid.) Jeps.
- Salix Glauca L. var. perstipulata Raup
- Salix Glauca L. var. poliophylla (C.K. Schneid.) Raup
- Salix Glauca L. var. pseudolapponum (Seemen) L. Kelso
- Salix Glauca L. var. seemanii (Rydb.) Ostenf.
- Salix Glauca L. var. sericea Hultén
- Salix Glauca L. var. stenolepis Polunin
- Salix Glauca L. var. stipulata Flod.
- Salix Glauca L. var. subincurva (E.H. Kelso) L. Kelso
- Salix Glaucophylla Bebb var. albovestita C.R. Ball
- Salix Glaucophylla Bebb var. angustifolia C.F. Wheeler & E.F. Sm.
- Salix Glaucophylla Bebb var. brevifolia C.F. Wheeler & E.F. Sm.
- Salix Glaucophylla Bebb var. latifolia C.F. Wheeler & E.F. Sm.
- Salix Glaucophylla Bebb, non Besser nec Andersson
- Salix Glaucophylloides Fernald
- Salix Glaucophylloides Fernald var. albovestita (C.R. Ball) Fernald
- Salix Glaucophylloides Fernald var. brevifolia (C.F. Wheeler & E.F. Sm.) C.R. Ball ex E
- Salix Glaucophylloides Fernald var. glaucophylla (Bebb) C.K. Schneid.
- Salix Glaucops Andersson
- Salix Glaucops Andersson var. glabrescens Andersson
- Salix Glaucops Andersson var. villosa (D. Don ex Hook.) Andersson
- Salix Gooddingii C.R. Ball var. vallicola (Dudley) C.R. Ball
- Salix Gooddingii C.R. Ball var. variabilis C.R. Ball
- Salix Gracilis Andersson
- Salix Gracilis Andersson var. rosmarinoides Andersson
- Salix Gracilis Andersson var. textoris Fernald
- Salix Gracilistyla Miq. var. melanostachys (Makino) C.K. Schneid.
- Salix Grisea Willd.
- Salix Groenlandica Lundstr. var. lejocarpa (Andersson) Lange
- Salix Groenlandica Lundstr., non Heer
- Salix Harbisonii C.K. Schneid.
- Salix Hastata L. ssp. subintegrifolia (Flod.) Flod.
- Salix Hastata L. var. farriae (C.R. Ball) Hultén
- Salix Hastata L. var. subintegrifolia Flod.
- Salix Hebecarpa (Fernald) Fernald
- Salix Hindsiana Benth.
- Salix Hindsiana Benth. var. leucodendroides (Rowlee) C.R. Ball
- Salix Hindsiana Benth. var. parishiana (Rowlee) C.R. Ball
- Salix Hindsiana Benth. var. tenuifolia (Andersson) Andersson
- Salix Hookeriana Barratt ex Hook. var. laurifolia J.K. Henry
- Salix Hookeriana Barratt ex Hook. var. tomentosa J.K. Henry ex C.K. Schneid.
- Salix Hoyeriana Dieck
- Salix Hudsonensis C.K. Schneid.
- Salix Humboldtiana Willd. var. fastigiata André
- Salix Humilis Marshall var. angustifolia (Barratt) Andersson
- Salix Humilis Marshall var. grandifolia (Barratt) Andersson
- Salix Humilis Marshall var. hyporhysa Fernald
- Salix Humilis Marshall var. keweenawensis Farw.
- Salix Humilis Marshall var. microphylla (Andersson) Fernald
- Salix Humilis Marshall var. rigidiuscula (Andersson) B.L. Rob. & Fernald
- Salix Humillima Andersson
- Salix Humillima Andersson var. puberula (Andersson) Andersson
- Salix Idahoensis (C.R. Ball) Rydb.
- Salix Incana Schrank
- Salix Interior Rowlee var. angustissima (Andersson) Dayton
- Salix Interior Rowlee var. exterior Fernald
- Salix Interior Rowlee var. luteosericea (Rydb.) C.K. Schneid.
- Salix Interior Rowlee var. pedicellata (Andersson) C.R. Ball
- Salix Interior Rowlee var. wheeleri Rowlee
- Salix Ivigtutiana Lundstr.
- Salix Kobayashii Kimura
- Salix Koreensis Andersson
- Salix Labradorica Rydb.
- Salix Labradorica Rydb. var. pumila Nutt.
- Salix Laevigata Bebb var. angustifolia Bebb ex Rothr.
- Salix Laevigata Bebb var. araquipa (Jeps.) C.R. Ball
- Salix Laevigata Bebb var. congesta Bebb ex Rothr.
- Salix Lanata L. ssp. calcicola (Fernald & Wiegand) Hultén
- Salix Lanata L. ssp. richardsonii (Hook.) Skvort.
- Salix Lancifolia Andersson
- Salix Lasiandra Benth.
- Salix Lasiandra Benth. ssp. caudata (Nutt.) A.E. Murray
- Salix Lasiandra Benth. var. abramsii C.R. Ball
- Salix Lasiandra Benth. var. caudata (Nutt.) Sudw.
- Salix Lasiandra Benth. var. fendleriana (Andersson) Bebb
- Salix Lasiandra Benth. var. lancifolia (Andersson) Bebb
- Salix Lasiandra Benth. var. lyallii Sarg.
- Salix Lasiandra Benth. var. macrophylla (Andersson) Little
- Salix Lasiandra Benth. var. recomponens Raup
- Salix Lasiolepis Benth. var. bakeri (Seemen) C.R. Ball
- Salix Lasiolepis Benth. var. bracelinae C.R. Ball
- Salix Lasiolepis Benth. var. fallax Bebb
- Salix Lasiolepis Benth. var. nivaria Jeps.
- Salix Lasiolepis Benth. var. sandbergii (Rydb.) C.R. Ball
- Salix Leiocarpa (Cham.) Coville
- Salix Leiolepis Fernald
- Salix Lemmonii Bebb var. austinae (Bebb) C.K. Schneid.
- Salix Lemmonii Bebb var. macrostachya Bebb
- Salix Lemmonii Bebb var. melanopsis Bebb
- Salix Lemmonii Bebb var. sphaerostachya Bebb
- Salix Ligustrina Michx. f.
- Salix Linearifolia Rydb.
- Salix Lingulata Andersson
- Salix Livida Wahlenb. var. occidentalis (Andersson) A. Gray
- Salix Livida Wahlenb. var. rostrata (Richardson) Dippel
- Salix Longifolia Muhl. var. argophylla (Nutt.) Andersson
- Salix Longifolia Muhl. var. exigua (Nutt.) Bebb
- Salix Longifolia Muhl. var. interior (Rowlee) M.E. Jones
- Salix Longifolia Muhl. var. opaca Andersson
- Salix Longifolia Muhl. var. pedicellata Andersson
- Salix Longifolia Muhl. var. sericans Nees
- Salix Longifolia Muhl. var. sessilifolia (Nutt.) M.E. Jones
- Salix Longifolia Muhl. var. tenerrima L.F. Hend.
- Salix Longifolia Muhl. var. wheeleri (Rowlee) C.K. Schneid.
- Salix Longifolia Muhl., non Lam.
- Salix Longipes Shuttlw. ex Andersson
- Salix Longipes Shuttlw. ex Andersson var. pubescens Andersson
- Salix Longipes Shuttlw. ex Andersson var. venulosa (Andersson) C.K. Schneid.
- Salix Longipes Shuttlw. ex Andersson var. wardii (Bebb) C.K. Schneid.
- Salix Longirostris Michx.
- Salix Longistylis Rydb.
- Salix Lucida Muhl. var. angustifolia (Andersson) Andersson
- Salix Lucida Muhl. var. intonsa Fernald
- Salix Lucida Muhl. var. latifolia (Andersson) Andersson
- Salix Lucida Muhl. var. macrophylla Andersson
- Salix Lucida Muhl. var. ovatifolia Andersson
- Salix Lucida Muhl. var. serissima L.H. Bailey
- Salix Ludoviciana Raf.
- Salix Lutea Nutt. var. desolata E.H. Kelso
- Salix Lutea Nutt. var. famelica C.R. Ball
- Salix Lutea Nutt. var. ligulifolia C.R. Ball
- Salix Lutea Nutt. var. nivaria Jeps.
- Salix Lutea Nutt. var. platyphylla C.R. Ball
- Salix Lutea Nutt. var. turnorii (Raup) B. Boivin
- Salix Lutea Nutt. var. watsonii (Bebb) Jeps.
- Salix Luteosericea Rydb.
- Salix Lyallii (Sarg.) A. Heller
- Salix Mackenzieana (Hook.) Barratt ex Andersson
- Salix Mackenzieana (Hook.) Barratt ex Andersson var. macrogemma C.R. Ball
- Salix Macounii Rydb.
- Salix Macrocarpa Nutt.
- Salix Macrocarpa Nutt. var. argentea Bebb
- Salix Macrostachya Nutt.
- Salix Macrostachya Nutt. var. cusickii Rowlee
- Salix Macrostachya Nutt. var. leucodendroides Rowlee
- Salix Malacophylla Nutt. ex C.R. Ball
- Salix Melanopsis Nutt. var. bolanderiana (Rowlee) C.K. Schneid.
- Salix Melanopsis Nutt. var. gracilipes C.R. Ball
- Salix Melanopsis Nutt. var. kronkheittii L. Kelso
- Salix Melanopsis Nutt. var. tenerrima (L.F. Hend.) C.R. Ball
- Salix Meleina (J.K. Henry) G.N. Jones
- Salix Mielichhoferi Saut.
- Salix Missouriensis Bebb
- Salix Miyabeana Seemen
- Salix Monica Bebb
- Salix Monticola Bebb var. neomexicana E.H. Kelso
- Salix Muehlenbergiana Willd.
- Salix Muehlenbergiana Willd. var. angustifolia Barratt
- Salix Muehlenbergiana Willd. var. grandifolia Barratt
- Salix Muriei Hultén
- Salix Muscina Dode ex Flod.
- Salix Myricoides Muhl. var. angustata (Pursh) Dippel
- Salix Myricoides Muhl. var. cordata (Muhl.) Dippel
- Salix Myricoides Muhl. var. rigida (Muhl.) Dippel
- Salix Myrsinites L. var. curtiflora Andersson, nom. inq.
- Salix Myrsinites L. var. jacquiniana (Willd.) W.D.J. Koch
- Salix Myrsinites L. var. parvifolia Lange
- Salix Myrtillifolia Andersson var. brachypoda Fernald
- Salix Myrtillifolia Andersson var. cordata (Andersson) Dorn
- Salix Myrtillifolia Andersson var. curtiflora (Andersson) Bebb ex Rose
- Salix Myrtillifolia Andersson var. curtiflora auct. non (Andersson) Bebb ex Rose
- Salix Myrtillifolia Andersson var. lingulata (Andersson) C.R. Ball
- Salix Myrtillifolia Andersson var. pseudomyrsinites (Andersson) C.R. Ball ex Hultén
- Salix Myrtillifolia auct. non Andersson
- Salix Myrtilloides L. var. hypoglauca (Fernald) C.R. Ball
- Salix Myrtilloides L. var. pedicellaris (Pursh) Andersson
- Salix Nelsonii C.R. Ball
- Salix Neoforbesii Toepffer
- Salix Nevadensis S. Watson
- Salix Nigra Marshall var. altissima Sarg.
- Salix Nigra Marshall var. amygdaloides (Andersson) Andersson
- Salix Nigra Marshall var. brevifolia Andersson
- Salix Nigra Marshall var. brevijulis Andersson
- Salix Nigra Marshall var. falcata (Pursh) Torr.
- Salix Nigra Marshall var. lindheimeri C.K. Schneid.
- Salix Nigra Marshall var. longifolia Andersson
- Salix Nigra Marshall var. longipes (Shuttlw. ex Andersson) Bebb
- Salix Nigra Marshall var. marginata (Wimm. ex Andersson) Andersson
- Salix Nigra Marshall var. vallicola Dudley
- Salix Nigra Marshall var. wardii Bebb
- Salix Nigra Marshall var. wrightii (Andersson) Andersson
- Salix Niphoclada Rydb. var. fullertonensis (C.K. Schneid.) Raup
- Salix Niphoclada Rydb. var. mexiae (C.R. Ball) Hultén
- Salix Niphoclada Rydb. var. muriei (Hultén) Raup
- Salix Nivalis Hook. var. saximontana (Rydb.) C.K. Schneid.
- Salix Novae-angliae Andersson var. myrtillifolia (Andersson) Andersson
- Salix Novae-angliae Andersson var. pseudocordata Andersson
- Salix Novae-angliae Andersson var. pseudomyrsinites (Andersson) Andersson
- Salix Novae-angliae auct. non Andersson
- Salix Nudescens Rydb.
- Salix Nummularia Andersson ssp. tundricola (Schljak.) Á. Löve & D. Löve
- Salix Nuttallii Sarg.
- Salix Nuttallii Sarg. var. capreoides (Andersson) Sarg.
- Salix Obovata Pursh
- Salix Occidentalis Bosc ex K. Koch var. longipes (Shuttlw. ex Andersson) Bebb
- Salix Occidentalis Bosc ex K. Koch, non Walter
- Salix Occidentalis Walter
- Salix Oleifolia Sm., non Vill.
- Salix Orbicularis Andersson
- Salix Ormsbyensis Seemen
- Salix Ovalifolia Trautv. var. camdensis C.K. Schneid.
- Salix Oxica Dode
- Salix Pachnophora Rydb.
- Salix Padifolia Rydb., non Andersson
- Salix Padophylla Rydb.
- Salix Paleoneura Rydb.
- Salix Pallasii Andersson
- Salix Pallasii Andersson var. crassijulis (Trautv.) Andersson
- Salix Paraleuca Fernald, database artifact
- Salix Parishiana Rowlee
- Salix Parksiana C.R. Ball
- Salix Pedicellaris Pursh var. athabascensis (Raup) B. Boivin
- Salix Pedicellaris Pursh var. hypoglauca Fernald
- Salix Pedicellaris Pursh var. tenuescens Fernald
- Salix Pellita Andersson var. angustifolia (Bebb) B. Boivin
- Salix Pendulina Wender. var. blanda (Andersson) Meikle ex anon., ined.
- Salix Pendulina Wender. var. elegantissima (K. Koch) Meikle
- Salix Pennata C.R. Ball
- Salix Pensylvanica Forbes
- Salix Pentandra L. var. caudata Nutt.
- Salix Pentandra L. var. lucida (Muhl.) Kuntze
- Salix Perrostrata Rydb.
- Salix Petiolaris Sm. var. angustifolia Andersson
- Salix Petiolaris Sm. var. gracilis (Andersson) Andersson
- Salix Petiolaris Sm. var. grisea (Willd.) Torr.
- Salix Petiolaris Sm. var. rosmarinoides (Andersson) C.K. Schneid.
- Salix Petiolaris Sm. var. sericea (Marshall) Andersson
- Salix Petiolaris Sm. var. subsericea Andersson
- Salix Petrophila Rydb. var. caespitosa (Kennedy) C.K. Schneid.
- Salix Phylicifolia L. ssp. planifolia (Pursh) Hiitonen
- Salix Phylicifolia L. ssp. pulchra (Cham.) Hultén
- Salix Phylicifolia L. var. monica (Bebb) Jeps.
- Salix Phylicifolia L. var. pennata (C.R. Ball) Cronquist
- Salix Phylicifolia L. var. subglauca (Andersson) B. Boivin
- Salix Phylicoides Andersson
- Salix Piperi Bebb
- Salix Pitcheriana Barratt
- Salix Planifolia Pursh ssp. pulchra (Cham.) Argus
- Salix Planifolia Pursh ssp. tyrrellii (Raup) Argus
- Salix Planifolia Pursh var. monica (Bebb) C.K. Schneid.
- Salix Planifolia Pursh var. nelsonii (C.R. Ball) C.R. Ball ex E.C. Sm.
- Salix Planifolia Pursh var. pennata (C.R. Ball) C.R. Ball ex Dutilly, Lepage & Da
- Salix Planifolia Pursh var. yukonensis (C.K. Schneid.) Argus
- Salix Polaris Wahlenb. ssp. pseudopolaris (Flod.) Hultén
- Salix Polaris Wahlenb. var. glabrata Hultén
- Salix Polaris Wahlenb. var. leiocarpa Cham.
- Salix Polaris Wahlenb. var. selwynensis Raup
- Salix Prinoides Pursh
- Salix Pseudocordata (Andersson) Rydb.
- Salix Pseudocordata (Andersson) Rydb. var. aequalis (Andersson) C.R. Ball ex C.K. Sc
- Salix Pseudocordata (Andersson) Rydb. var. cordata (Andersson) C.R. Ball
- Salix Pseudocordata auct. non (Andersson) Rydb.
- Salix Pseudolapponum Seemen
- Salix Pseudolapponum Seemen var. kenosha L. Kelso
- Salix Pseudolapponum Seemen var. subincurva E.H. Kelso
- Salix Pseudomonticola C.R. Ball var. padophylla (Rydb.) C.R. Ball
- Salix Pseudomyrsinites Andersson var. aequalis (Andersson) Andersson ex C.R. Ball
- Salix Pseudomyrsinites auct. non Andersson
- Salix Pseudopolaris Flod.
- Salix Pulchra Cham. var. looffiae C.R. Ball
- Salix Pulchra Cham. var. palmeri C.R. Ball
- Salix Pulchra Cham. var. yukonensis C.K. Schneid.
- Salix Purpurea L. f. gracilis (Gren. & Godr.) C.K. Schneid.
- Salix Purpurea L. var. nana Dieck
- Salix Purshiana Spreng.
- Salix Pychnocarpa Andersson
- Salix Pyrifolia Andersson var. lanceolata (Bebb) Fernald
- Salix Pyrolifolia Andersson var. hoyeriana (Dieck) Dippel
- Salix Recurvata Pursh
- Salix Regelii Andersson
- Salix Reticulata L. ssp. nivalis (Hook.) Á. Löve & D. Löve & Kapoor
- Salix Reticulata L. ssp. orbicularis (Andersson) Flod.
- Salix Reticulata L. var. gigantifolia C.R. Ball
- Salix Reticulata L. var. glabra Trautv.
- Salix Reticulata L. var. nana (Hook.) Andersson
- Salix Reticulata L. var. nivalis (Hook.) Andersson
- Salix Reticulata L. var. orbicularis (Andersson) Kom.
- Salix Reticulata L. var. saximontana (Rydb.) L. Kelso
- Salix Reticulata L. var. semicalva Fernald
- Salix Reticulata L. var. vestita (Pursh) Andersson
- Salix Richardsonii Hook. var. macouniana Bebb
- Salix Richardsonii Hook. var. mckeandii Polunin
- Salix Rigida Muhl.
- Salix Rigida Muhl. ssp. ligulifolia (C.R. Ball) A.E. Murray
- Salix Rigida Muhl. ssp. mackenzieana (Hook.) A.E. Murray
- Salix Rigida Muhl. var. angustata (Pursh) Fernald
- Salix Rigida Muhl. var. mackenzieana (Hook.) Cronquist
- Salix Rigida Muhl. var. macrogemma (C.R. Ball) Cronquist
- Salix Rigida Muhl. var. vestita (Andersson) C.R. Ball
- Salix Rigida Muhl. var. watsonii (Bebb) Cronquist
- Salix Rosmarinifolia L.
- Salix Rostrata Richardson var. capreifolia Fernald
- Salix Rostrata Richardson var. luxurians Fernald
- Salix Rostrata Richardson var. perrostrata (Rydb.) Fernald
- Salix Rostrata Richardson var. projecta Fernald
- Salix Rostrata Richardson, non Thuill.
- Salix Rotundata Rydb. ex Macoun
- Salix Rotundifolia Nutt., non Trautv.
- Salix Rotundifolia Trautv. var. dodgeana (Rydb.) A.E. Murray
- Salix Rubra Richardson, non Huds.
- Salix Rydbergii A. Heller
- Salix Sachalinensis F. Schmidt
- Salix Salamonii (Carrière) Carrière
- Salix Salomonii hort., database artifact
- Salix Sandbergii Rydb.
- Salix Saskatchevana Seemen
- Salix Sawatchicola L. Kelso
- Salix Saximontana Rydb.
- Salix Scouleriana Barratt ex Hook. var. brachystachys (Benth.) M.E. Jones
- Salix Scouleriana Barratt ex Hook. var. coetanea C.R. Ball
- Salix Scouleriana Barratt ex Hook. var. crassijulis (Andersson) C.K. Schneid.
- Salix Scouleriana Barratt ex Hook. var. flavescens (Nutt.) J.K. Henry
- Salix Scouleriana Barratt ex Hook. var. poikila C.K. Schneid.
- Salix Scouleriana Barratt ex Hook. var. thompsonii C.R. Ball
- Salix Seemanii Rydb.
- Salix Sensitiva Barratt
- Salix Sericea Marshall var. subsericea (Andersson) Rydb.
- Salix Seriocarpa Buser
- Salix Sessilifolia Nutt. ssp. hindsiana (Benth.) Andersson
- Salix Sessilifolia Nutt. var. hindsiana (Benth.) Andersson
- Salix Sessilifolia Nutt. var. leucodendroides (Rowlee) C.K. Schneid.
- Salix Sessilifolia Nutt. var. vancouverensis Brayshaw
- Salix Sessilifolia Nutt. var. villosa Andersson
- Salix Sitchensis Sanson ex Bong. var. angustifolia Bebb
- Salix Sitchensis Sanson ex Bong. var. congesta (Andersson) Andersson
- Salix Sitchensis Sanson ex Bong. var. denudata (Andersson) Andersson
- Salix Sitchensis Sanson ex Bong. var. parviflora (Jeps.) Jeps.
- Salix Sitchensis Sanson ex Bong. var. pellita (Andersson) Jeps.
- Salix Sitchensis Sanson ex Bong. var. ralphiana (Jeps.) Jeps.
- Salix Speciosa Hook. & Arn. var. alaxensis Andersson
- Salix Speciosa Hook. & Arn., non Host nec Nutt.
- Salix Speciosa Nutt., non Host nec Hook. & Arn.
- Salix Sphenophylla Skvort. ssp. pseudotorulosa Skvort.
- Salix Squamata Rydb.
- Salix Stagnalis Nutt.
- Salix Starkeana Willd. ssp. bebbiana (Sarg.) Youngberg
- Salix Stenocarpa Fernald
- Salix Stenophylla Rydb.
- Salix Stipulifera Flod. ex Hayren
- Salix Stricta (Andersson) Rydb.
- Salix Subcaerulea Piper
- Salix Subcordata Andersson
- Salix Suksdorfii Gandog.
- Salix Syrticola Fernald
- Salix Taxifolia Kunth var. lejocarpa Andersson
- Salix Taxifolia Kunth var. limitanea I.M. Johnst.
- Salix Taxifolia Kunth var. seriocarpa Andersson
- Salix Tenera Andersson
- Salix Tenerrima (L.F. Hend.) A. Heller
- Salix Thurberi Rowlee
- Salix Torreyana Barratt
- Salix Tortulosa Trautv.
- Salix Toumeyi Britton & Shafer
- Salix Tristis Aiton
- Salix Tristis Aiton var. glabrata (Andersson) Andersson
- Salix Tristis Aiton var. longifolia Andersson
- Salix Tristis Aiton var. microphylla Andersson
- Salix Tristis Aiton var. momadelphia Barratt
- Salix Tundricola Schljak.
- Salix Udensis Trautv. & C.A. Mey.
- Salix Unalaschensis Cham.
- Salix Vacciniformis Rydb.
- Salix Vagans Hook. f. ex Andersson var. occidentalis Andersson
- Salix Vagans Hook. f. ex Andersson var. rostrata (Richardson) Andersson
- Salix Vallicola (Dudley) Britton & Shafer
- Salix Variegata Franch.
- Salix Venusta Andersson
- Salix Vestita Pursh ssp. leiolepis (Fernald) Argus
- Salix Vestita Pursh var. erecta Andersson
- Salix Vestita Pursh var. humilior Andersson
- Salix Vestita Pursh var. nana Hook.
- Salix Vestita Pursh var. psilophylla Fernald & H. St. John
- Salix Villosa D. Don ex Hook.
- Salix Villosa D. Don ex Hook. var. acutifolia Hook.
- Salix Vitellina L.
- Salix Walpolei (Coville & C.R. Ball) C.R. Ball
- Salix Wardii (Bebb) Bebb
- Salix Watsonii (Bebb) Rydb.
- Salix Wheeleri (Rowlee) Rydb.
- Salix Wolfii Bebb ssp. idahoensis (C.R. Ball) A.E. Murray
- Salix Wolfii Bebb var. idahoensis C.R. Ball
- Salix Wolfii Bebb var. pseudolapponum (Seemen) M.E. Jones
- Salix Wrightii Andersson
- Salix Wyomingensis Rydb.
- Salix ×blanda Andersson (pro sp.)
- Salix ×chrysocoma Dode
- Salix ×dichroa Döll
- Salix ×hankensonii Dode [excluded]
- Salix ×jesupii Fernald
- Salix ×laestadiana Hartm.
- Salix ×paraleuca Fernald
- Salix ×pellicolor Lepage
- Salix ×pontederana Willd.
- Salix ×sepulcralis Simonkai var. chrysocoma (Dode) Meikle
- Salix ×simulatrix F.B. White
- Salix ×subsericea (Andersson) C.K. Schneid.
- Salmalia Malabarica (DC.) Schott & Endl.
- Salmon Barberry - Berberis Aggregata C.K. Schneid.
- Salmon Creek Indian Paintbrush - Castilleja Praeterita Heckard & Bacig.
- Salmon Gum - Eucalyptus Salmonophloia F. Muell.
- Salmon River Beardtongue - Penstemon Pumilus Nutt.
- Salmon River Cryptantha - Cryptantha Salmonensis (A. Nelson & J.F. Macbr.) Payson
- Salmon River Fleabane - Erigeron Salmonensis S.J. Brunsfeld & G.L. Nesom
- Salmon River Locoweed - Oxytropis Besseyi (Rydb.) Blank. var. salmonensis Barneby
- Salmon Wildrye - Leymus Salinus (M.E. Jones) Á. Löve ssp. salmonis (C.L. Hitchc.) Atkins
- Salmonberry - Rubus Spectabilis Pursh
- Salmonberry - Rubus Spectabilis Pursh var. franciscanus (Rydb.) J.T. Howell
- Salmonberry - Rubus Spectabilis Pursh var. spectabilis
- Salmonflower Biscuitroot - Lomatium Salmoniflorum (J.M. Coult. & Rose) Mathias & Constance
- Salomonia Cantoniensis Lour.
- Salomonia Ciliata (L.) DC.
- Salomonia Cobrensis Wooton & Standl.
- Salomonia Lour.
- Salpichroa Rhomboidea (Gillies & Hook.) Miers
- Salpichroa - Salpichroa Miers
- Salpiglossis Erecta (DC.) D'Arcy
- Salpiglossis - Salpiglossis K. Koch
- Salpingia Hartwegii (Benth.) Raimann
- Salpingostylis Coelestina (W. Bartram) Small
- Salsedo's Timonius - Timonius Salsedoi Fosberg & Sachet
- Salsify - Tragopogon Porrifolius L.
- Salsola Australis R. Br.
- Salsola Caroliniana Walter
- Salsola Damascena Botsch.
- Salsola Iberica (Sennen & Pau) Botsch. ex Czerep.
- Salsola Kali L. ssp. ruthenica (Iljin) Soó
- Salsola Kali L. ssp. tenuifolia Moq.
- Salsola Kali L. ssp. tragus (L.) Celak.
- Salsola Kali L. var. caroliniana (Walter) Nutt.
- Salsola Kali L. var. pontica Pall.
- Salsola Pestifer A. Nelson
- Salsola Pontica (Pall.) A. Degen
- Salsola Ruthenica Iljin
- Salt Gilia - Gilia Salticola Eastw.
- Salt Heliotrope - Heliotropium Curassavicum L.
- Salt Heliotrope - Heliotropium Curassavicum L. var. curassavicum
- Salt River Rockdaisy - Perityle Gilensis (M.E. Jones) J.F. Macbr. var. salensis A. Powell
- Salt Rush - Juncus Lesueurii Bol.
- Salt Sandspurry - Spergularia Salina J. Presl & C. Presl
- Salt Sedge - Carex Hassei L.H. Bailey
- Salt Spring Checkerbloom - Sidalcea Neomexicana A. Gray
- Salt Spring Checkerbloom - Sidalcea Neomexicana A. Gray ssp. crenulata (A. Nelson) C.L. Hitchc.
- Salt Spring Checkerbloom - Sidalcea Neomexicana A. Gray ssp. neomexicana
- Saltbush - Atriplex Halimus L.
- Saltbush - Atriplex L.
- Saltbush - Atriplex ×odontoptera Rydb. (pro sp.)
- Saltbush - Enchylaena R. Br.
- Saltcedar - Tamarix Ramosissima Ledeb.
- Saltgrass - Distichlis Raf.
- Saltgrass - Distichlis Spicata (L.) Greene
- Saltlover - Halogeton C.a. Mey.
- Saltlover - Halogeton Glomeratus (M. Bieb.) C.A. Mey.
- Saltloving Goosefoot - Chenopodium Macrospermum Hook. f. var. halophilum (Phil.) Standl.
- Saltmarsh Alkaligrass - Puccinellia Fasciculata (Torr.) E.P. Bicknell
- Saltmarsh Baccharis - Baccharis Douglasii DC.
- Saltmarsh Bird's-beak - Cordylanthus Maritimus Nutt. ex Benth.
- Saltmarsh Bird's-beak - Cordylanthus Maritimus Nutt. ex Benth. ssp. canescens (A. Gray) T.I. Chuang & Heckard
- Saltmarsh Bird's-beak - Cordylanthus Maritimus Nutt. ex Benth. ssp. maritimus
- Saltmarsh Dodder - Cuscuta Salina Engelm.
- Saltmarsh Dodder - Cuscuta Salina Engelm. var. salina
- Saltmarsh False Foxglove - Agalinis Maritima (Raf.) Raf.
- Saltmarsh False Foxglove - Agalinis Maritima (Raf.) Raf. var. grandiflora (Benth.) Shinners
- Saltmarsh False Foxglove - Agalinis Maritima (Raf.) Raf. var. maritima
- Saltmarsh Fingergrass - Eustachys Glauca Chapm.
- Saltmarsh Morning-glory - Ipomoea Sagittata Poir.
- Saltmarsh Sea Lavender - Limonium Otolepis (Schrenk) Kuntze
- Saltmarsh Sedge - Carex Salina Wahlenb.
- Saltmarsh Spikerush - Eleocharis Halophila (Fernald & Brack.) Fernald & Brack.
- Saltmarsh Starwort - Stellaria Humifusa Rottb.
- Saltmarsh Umbrella-sedge - Fuirena Breviseta (Coville) Coville
- Saltmeadow Cordgrass - Spartina Patens (Aiton) Muhl.
- Saltmeadow Plantain - Plantago Argyrea Morris
- Saltmeadow Rush - Juncus Gerardii Loisel.
- Saltmeadow Rush - Juncus Gerardii Loisel. var. gerardii
- Saltmeadow Rush - Juncus Gerardii Loisel. var. pedicellatus Fernald
- Salton Milkvetch - Astragalus Crotalariae (Benth.) A. Gray
- Saltugilia Grinnellii (Brand) L.A. Johnson ssp. grantii (Brand) L.A. Johnson
- Saltugilia Grinnellii (Brand) L.A. Johnson, nom. utique rej.
- Saltugilia - Saltugilia (v.e. Grant) L.A. Johnson
- Saltugilia - Saltugilia Latimeri T.L. Weese & L.A. Johnson
- Saltwater Bush - Rachicallis Americana (Jacq.) Kuntze
- Saltwater Bush - Rachicallis Dc.
- Saltwater Cress - Thellungiella Al-shehbaz
- Saltwater Cress - Thellungiella Salsuginea (Pall.) O.E. Schulz
- Saltwater False Willow - Baccharis Angustifolia Michx.
- Saltwood - Neea Buxifolia (Hook. f.) Heimerl
- Saltwood - Neea Ruiz & Pav.
- Saltwort Buckwheat - Eriogonum Salicornioides Gandog.
- Salty Buckwheat - Stenogonum Salsuginosum Nutt.
- Salty Loco Milkvetch - Astragalus Lentiginosus Douglas ex Hook. var. salinus (Howell) Barneby
- Salty Popcornflower - Plagiobothrys Salsus (Brandegee) I.M. Johnst.
- Salvation Jane - Echium Plantagineum L.
- Salvia Aurea L.
- Salvia Azurea Michx. ex Lam. ssp. intermedia Epling
- Salvia Azurea Michx. ex Lam. ssp. pitcheri (Torr. ex Benth.) Epling
- Salvia Ballotiflora Benth. var. pinguifolia Fernald
- Salvia Blodgettii Chapm.
- Salvia Broussonetii Benth.
- Salvia Carnosa Douglas ex Greene
- Salvia Carnosa Douglas ex Greene ssp. argentea (Rydb.) Epling
- Salvia Carnosa Douglas ex Greene ssp. gilmanii Epling
- Salvia Carnosa Douglas ex Greene ssp. mearnsii (Britton) Epling
- Salvia Carnosa Douglas ex Greene ssp. pilosa (A. Gray) Epling
- Salvia Carnosa Douglas ex Greene var. argentea (Rydb.) McMinn
- Salvia Carnosa Douglas ex Greene var. gilmanii (Epling) L.D. Benson
- Salvia Carnosa Douglas ex Greene var. gracilior M. Peck
- Salvia Chia Fernald
- Salvia Cistus - Cistus Salviifolius L.
- Salvia Cleistogama de Bary & Paul
- Salvia Dolichantha (Cory) Whitehouse
- Salvia Dominica L.
- Salvia Dorrii (Kellogg) Abrams ssp. argentea (Rydb.) Munz
- Salvia Dorrii (Kellogg) Abrams ssp. carnosa (Douglas ex Greene) Abrams
- Salvia Dorrii (Kellogg) Abrams ssp. gilmanii (Epling) Abrams
- Salvia Dorrii (Kellogg) Abrams var. carnosa (Douglas ex Greene) Cronquist
- Salvia Earlei Wooton & Standl.
- Salvia Eigii Zohary
- Salvia Farinacea Benth. var. farinacea
- Salvia Farinacea Benth. var. latifolia Shinners
- Salvia Grahamii Benth.
- Salvia Indica L.
- Salvia Judaica Boiss.
- Salvia Jurisicii Kosanin
- Salvia Lancifolia Poir.
- Salvia Lanigera Poir.
- Salvia Leptophylla Benth.
- Salvia Mellifera Greene ssp. jonesii (Munz) Abrams
- Salvia Mellifera Greene ssp. revoluta (Brandegee) Abrams
- Salvia Microphylla Benth. var. wislizeni A. Gray
- Salvia Microstegia Boiss. & Balansa
- Salvia Nemorosa L.
- Salvia Palaestina Benth.
- Salvia Penstemonoides Kunth & Bouché, orth. var.
- Salvia Pinnata L.
- Salvia Pitcheri Torr. ex Benth.
- Salvia Privoides Benth.
- Salvia Ramosissima Fernald
- Salvia Samuelssonii Rech. f.
- Salvia Sclarea L. var. turkestaniana Mottet
- Salvia Setosa Fernald [excluded]
- Salvia Spinosa L.
- Salvia Syriaca L.
- Salvia Verbenacea L., database artifact
- Salvia Virgata auct. non Jacq.
- Salvinia Auriculata auct. non Aubl.
- Salvinia Laevigata Humb. & Bonpl. ex Willd.
- Salvinia Natans auct. non (L.) All.
- Salvinia Rotundifolia Willd.
- Salvinia Rotundifolia auct. non Willd.
- Salzmann's Mille Graines - Oldenlandia Salzmannii (DC.) Benth. & Hook. f. ex B.D. Jacks.
- Samadera Gaertn.
- Sambucus Africana Standl.
- Sambucus Caerulea Raf. var. mexicana (C. Presl ex DC.) L.D. Benson, orth. var.
- Sambucus Caerulea Raf. var. neomexicana (Wooton) Rehder, orth. var.
- Sambucus Caerulea Raf. var. velutina (Durand & Hilg.) Schwerin, orth. var.
- Sambucus Caerulea Raf., orth. var.
- Sambucus Callicarpa Greene
- Sambucus Canadensis L.
- Sambucus Canadensis L. var. laciniata A. Gray
- Sambucus Canadensis L. var. submollis Rehder
- Sambucus Cerulea Raf.
- Sambucus Cerulea Raf. var. mexicana (C. Presl ex DC.) L.D. Benson
- Sambucus Cerulea Raf. var. neomexicana (Wooton) Rehder
- Sambucus Cerulea Raf. var. velutina (Durand & Hilg.) Schwerin
- Sambucus Coreana (Nakai) Kom. & Aliss.
- Sambucus Glauca Nutt.
- Sambucus Kamtschatica E.L. Wolf
- Sambucus Laciniata Mill.
- Sambucus Melanocarpa A. Gray
- Sambucus Mexicana C. Presl ex DC.
- Sambucus Mexicana C. Presl ex DC. ssp. caerulea (Raf.) A.E. Murray, orth. var.
- Sambucus Mexicana C. Presl ex DC. ssp. cerulea (Raf.) A.E. Murray
- Sambucus Mexicana C. Presl ex DC. var. caerulea (Raf.) A.E. Murray, orth. var.
- Sambucus Mexicana C. Presl ex DC. var. cerulea (Raf.) A.E. Murray
- Sambucus Microbotrys Rydb.
- Sambucus Neomexicana Wooton
- Sambucus Neomexicana Wooton var. vestita (Wooton & Standl.) Kearney & Peebles
- Sambucus Nigra L. ssp. caerulea (Raf.) R. Bolli, orth. var.
- Sambucus Nigra L. var. laciniata L.
- Sambucus Orbiculata Greene
- Sambucus Pubens Michx.
- Sambucus Pubens Michx. var. arborescens Torr. & A. Gray
- Sambucus Racemosa L. ssp. pubens (Michx.) House
- Sambucus Racemosa L. ssp. sibirica (Nakai) H. Hara
- Sambucus Racemosa L. ssp. sieboldiana (Miq.) H. Hara
- Sambucus Racemosa L. var. arborescens (Torr. & A. Gray) A. Gray
- Sambucus Racemosa L. var. laciniata W.D.J. Koch ex DC.
- Sambucus Racemosa L. var. leucocarpa (Torr. & A. Gray) Cronquist
- Sambucus Racemosa L. var. microbotrys (Rydb.) Kearney & Peebles
- Sambucus Racemosa L. var. pubens (Michx.) Koehne
- Sambucus Sibirica Nakai
- Sambucus Sieboldiana (Miq.) Blume ex Graebn.
- Sambucus Simpsonii Rehder ex Sarg.
- Sambucus Velutina Durand & Hilg.
- Samoan Oil Plant - Atuna Racemosa Raf.
- Samodia Ebracteata (Kunth) Baudo
- Samolus Alyssoides A. Heller
- Samolus Cuneatus Small
- Samolus Ebracteatus Kunth var. alyssoides (A. Heller) Henrickson
- Samolus Ebracteatus Kunth var. cuneatus (Small) Henrickson
- Samolus Floribundus Kunth
- Samolus Parviflorus Raf.
- Sampson's Snakeroot - Orbexilum Pedunculatum (Mill.) Rydb.
- Sampson's Snakeroot - Orbexilum Pedunculatum (Mill.) Rydb. var. pedunculatum
- Sampson's Snakeroot - Orbexilum Pedunculatum (Mill.) Rydb. var. psoralioides (Walter) Isely
- Samuela Carnerosana auct. non Trel.
- Samuela Faxoniana Trel.
- Samyda Guidonia L.
- Samyda - Samyda Jacq.
- Samyda Spinulosa auct. non Vent.
- San Andres Mountain Foxtail Cactus - Escobaria Sandbergii Castetter, Pierce & Schwerin
- San Angelo Yucca - Yucca Reverchonii Trel.
- San Anselmo Navarretia - Navarretia Rosulata Brand
- San Antoinio Canyon Bedstraw - Galium Angustifolium Nutt. ex A. Gray ssp. gabrielense (Munz & I.M. Johnst.) Dempster
- San Antonio Bluestar - Amsonia Fugatei S.P. McLaughlin
- San Antonio False Foxglove - Agalinis Homalantha Pennell
- San Antonio Hills Monardella - Monardella Antonina Hardham
- San Antonio Hills Monardella - Monardella Antonina Hardham ssp. antonina
- San Antonio Pricklypear - Opuntia Valida Griffiths
- San Antonio Stoneseed - Lithospermum Mirabile Small
- San Bartolome - Cordia Rickseckeri Millsp.
- San Benito Fritillary - Fritillaria Viridea Kellogg
- San Benito Monardella - Monardella Antonina Hardham ssp. benitensis (Hardam) Jokerst
- San Benito Onion - Allium Howellii Eastw. var. sanbenitense (Traub) Ownbey & Aase
- San Benito Poppy - Eschscholzia Hypecoides Benth.
- San Benito Spineflower - Chorizanthe Biloba Goodman var. immemora Reveal & Hardham
- San Benito Suncup - Camissonia Benitensis P.H. Raven
- San Benito Thorn-mint - Acanthomintha Obovata Jeps.
- San Benito Thorn-mint - Acanthomintha Obovata Jeps. ssp. obovata
- San Bernardino Aster - Symphyotrichum Defoliatum (Parish) G.L. Nesom
- San Bernardino Beardtongue - Penstemon Caesius A. Gray
- San Bernardino Bluegrass - Poa Atropurpurea Scribn.
- San Bernardino Buckwheat - Eriogonum Microthecum Nutt. var. corymbosoides Reveal
- San Bernardino Grass Of Parnassus - Parnassia Cirrata Piper
- San Bernardino Larkspur - Delphinium Parryi A. Gray
- San Bernardino Larkspur - Delphinium Parryi A. Gray ssp. parryi
- San Bernardino Larkspur - Delphinium Parryi A. Gray ssp. purpureum (F.H. Lewis & Epling) Warnock
- San Bernardino Milkvetch - Astragalus Bernardinus M.E. Jones
- San Bernardino Mountain Alumroot - Heuchera Alpestris Rosend., Butters & Lakela
- San Bernardino Mountain Gilia - Linanthus Maculatus (Parish) Milliken
- San Bernardino Mountain Monkeyflower - Mimulus Exiguus A. Gray
- San Bernardino Mountain Onion - Allium Monticola Davidson
- San Bernardino Mountains Indian Paintbrush - Castilleja Lasiorhyncha (A. Gray) T.I. Chuang & Heckard
- San Bernardino Mountains Liveforever - Dudleya Abramsii Rose ssp. affinis K.M. Nakai
- San Bernardino Ragwort - Packera Bernardina (Greene) W.A. Weber & Á. Löve
- San Bernardino Spineflower - Chorizanthe Parryi S. Watson
- San Bernardino Spineflower - Chorizanthe Parryi S. Watson var. parryi
- San Bernardino Suncup - Camissonia Confusa P.H. Raven
- San Bernardino Vervain - Verbena Abramsii Moldenke
- San Bruno Mountain Manzanita - Arctostaphylos Imbricata Eastw.
- San Carlos Buckwheat - Eriogonum Capillare Small
- San Clemente Island Brodiaea - Brodiaea Kinkiensis Niehaus
- San Clemente Island Buckwheat - Eriogonum Giganteum S. Watson var. formosum Brandegee
- San Clemente Island Bushmallow - Malacothamnus Clementinus (Munz & I.M. Johnst.) Kearney
- San Clemente Island Indian Paintbrush - Castilleja Grisea Dunkle
- San Clemente Island Milkvetch - Astragalus Nevinii A. Gray
- San Clemente Island Triteleia - Triteleia Clementina Hoover
- San Clemente Island Woodland-star - Lithophragma Maximum Bacig.
- San Diego Alpinegold - Hulsea Californica Torr. & A. Gray
- San Diego Barrelcactus - Ferocactus Viridescens (Torr. & A. Gray) Britton & Rose
- San Diego Bird's-foot Trefoil - Lotus Hamatus Greene
- San Diego Buckbrush - Ceanothus Cyaneus Eastw.
- San Diego Bur Ragweed - Ambrosia Chenopodiifolia (Benth.) Payne
- San Diego Bush Monkeyflower - Diplacus Aridus Abrams
- San Diego Coastalcreeper - Aphanisma Blitoides Nutt. ex Moq.
- San Diego Goldenstar - Muilla Clevelandii (S. Watson) Hoover
- San Diego Mesamint - Pogogyne Abramsii J.T. Howell
- San Diego Needlegrass - Achnatherum Diegoense (Swallen) Barkworth
- San Diego Nightshade - Solanum Tenuilobatum Parish
- San Diego Pepperweed - Lepidium Latipes Hook.
- San Diego Pepperweed - Lepidium Latipes Hook. var. latipes
- San Diego Pitchersage - Lepechinia Ganderi Epling
- San Diego Povertyweed - Iva Hayesiana A. Gray
- San Diego Raspberry - Rubus Glaucifolius Kellogg
- San Diego Raspberry - Rubus Glaucifolius Kellogg var. glaucifolius
- San Diego Sagewort - Artemisia Palmeri A. Gray
- San Diego Sedge - Carex Spissa L.H. Bailey
- San Diego Spineflower - Chorizanthe Orcuttiana Parry
- San Diego Tarweed - Hemizonia Paniculata A. Gray
- San Diego Thorn-mint - Acanthomintha Ilicifolia (A. Gray) A. Gray
- San Diego Wild Cabbage - Caulanthus Heterophyllus (Nutt.) Payson
- San Diego Wirelettuce - Stephanomeria Diegensis Gottlieb
- San Felipe Dogweed - Adenophyllum Porophylloides (A. Gray) Strother
- San Felipe Monardella - Monardella Nana A. Gray ssp. leptosiphon (Torr.) Abrams
- San Fernando Valley Spineflower - Chorizanthe Parryi S. Watson var. fernandina (S. Watson) Jeps.
- San Francisco Blue Eyed Mary - Collinsia Multicolor Lindl. & Paxton
- San Francisco Bluegrass - Poa Unilateralis Scribn.
- San Francisco Bluegrass - Poa Unilateralis Scribn. ssp. pachypholis (Piper) D.D. Keck ex Soreng
- San Francisco Bluegrass - Poa Unilateralis Scribn. ssp. unilateralis
- San Francisco Campion - Silene Verecunda S. Watson
- San Francisco Campion - Silene Verecunda S. Watson ssp. andersonii (Clokey) C.L. Hitchc. & Maguire
- San Francisco Campion - Silene Verecunda S. Watson ssp. platyota (S. Watson) C.L. Hitchc. & Maguire
- San Francisco Campion - Silene Verecunda S. Watson ssp. platyota (S. Watson) C.L. Hitchc. & Maguire var.
- San Francisco Campion - Silene Verecunda S. Watson ssp. platyota (S. Watson) C.L. Hitchc. & Maguire var.
- San Francisco Campion - Silene Verecunda S. Watson ssp. verecunda
- San Francisco Lessingia - Lessingia Germanorum Cham.
- San Francisco Nailwort - Paronychia Franciscana Eastw.
- San Francisco Onion - Allium Peninsulare Lemmon ex Greene var. franciscanum McNeal & Ownbey
- San Francisco Owl's-clover - Triphysaria Floribunda (Benth.) T.I. Chuang & Heckard
- San Francisco Peaks Ragwort - Packera Franciscana (Greene) W.A. Weber & Á. Löve
- San Francisco River Leatherpetal - Graptopetalum Rusbyi (Greene) Rose
- San Francisco Spineflower - Chorizanthe Cuspidata S. Watson
- San Francisco Spineflower - Chorizanthe Cuspidata S. Watson var. cuspidata
- San Francisco Spineflower - Chorizanthe Cuspidata S. Watson var. villosa (Eastw.) Munz
- San Francisco Wallflower - Erysimum Franciscanum G. Rossb.
- San Francisco Woodland-star - Lithophragma Affine A. Gray
- San Francisco Woodland-star - Lithophragma Affine A. Gray ssp. affine
- San Francisco Woodland-star - Lithophragma Affine A. Gray ssp. mixtum R.L. Taylor
- San Gabriel Alumroot - Heuchera Abramsii Rydb.
- San Gabriel Beardtongue - Penstemon Labrosus (A. Gray) Hook. f.
- San Gabriel Bedstraw - Galium Grande McClatchie
- San Gabriel Bluecup - Githopsis Diffusa A. Gray
- San Gabriel Bluecup - Githopsis Diffusa A. Gray ssp. candida (Ewan) Morin
- San Gabriel Bluecup - Githopsis Diffusa A. Gray ssp. diffusa
- San Gabriel Bluecup - Githopsis Diffusa A. Gray ssp. filicaulis (Ewan) Morin
- San Gabriel Bluecup - Githopsis Diffusa A. Gray ssp. robusta Morin
- San Gabriel Linanthus - Linanthus Concinnus Milliken
- San Gabriel Manzanita - Arctostaphylos Gabrielensis P.V. Wells
- San Gabriel Mountains Liveforever - Dudleya Densiflora (Rose) Moran
- San Gabriel Ragwort - Senecio Astephanus Greene
- San Gabriel River Dudleya - Dudleya Cymosa (Lem.) Britton & Rose ssp. crebrifolia K.M. Nakai & Verity
- San Jacinto Beardtongue - Penstemon Clevelandii A. Gray ssp. connatus (Munz & I.M. Johnst.) D.D. Keck
- San Jacinto Bedstraw - Galium Angustifolium Nutt. ex A. Gray ssp. jacinticum Dempster & Stebbins
- San Jacinto Bluecurls - Trichostema Austromontanum F.H. Lewis
- San Jacinto Bluecurls - Trichostema Austromontanum F.H. Lewis ssp. austromontanum
- San Jacinto Bluecurls - Trichostema Austromontanum F.H. Lewis ssp. compactum F.H. Lewis
- San Jacinto Buckwheat - Eriogonum Apiculatum S. Watson
- San Jacinto Lupine - Lupinus Hyacinthinus Greene
- San Jacinto Prickly Phlox - Linanthus Jaegeri (Munz) J.M. Porter & L.A. Johnson
- San Joaquin Adobe Sunburst - Pseudobahia Peirsonii Munz
- San Joaquin Blazingstar - Mentzelia Pectinata Kellogg
- San Joaquin Bluecurls - Trichostema Ovatum Curran
- San Joaquin Dodder - Cuscuta Brachycalyx (Yunck.) Yunck.
- San Joaquin Dodder - Cuscuta Brachycalyx (Yunck.) Yunck. var. apodanthera (Yunck.) Yunck.
- San Joaquin Dodder - Cuscuta Brachycalyx (Yunck.) Yunck. var. brachycalyx
- San Joaquin Milkvetch - Astragalus Asymmetricus Sheldon
- San Joaquin Saltbush - Atriplex Joaquinana A. Nelson
- San Joaquin Silverpuffs - Microseris Campestris Greene
- San Joaquin Snakeweed - Gutierrezia Californica (DC.) Torr. & A. Gray
- San Joaquin Tarweed - Holocarpha Obconica (J.C. Clausen & D.D. Keck) D.D. Keck
- San Joaquin Tarweed - Holocarpha Obconica (J.C. Clausen & D.D. Keck) D.D. Keck ssp. autumnalis D.D. Keck
- San Joaquin Tarweed - Holocarpha Obconica (J.C. Clausen & D.D. Keck) D.D. Keck ssp. obconica
- San Joaquin Valley Orcutt Grass - Orcuttia Inaequalis Hoover
- San Joaquin Woollythread - Monolopia Congdonii (A. Gray) B.G. Baldw.
- San Juan Gilia - Aliciella Haydenii (A. Gray) J.M. Porter
- San Juan Milkvetch - Astragalus Chuskanus Barneby & Spellenb.
- San Lorenzo Milkvine - Matelea Borinquensis Alain
- San Luis Blazingstar - Mentzelia Micrantha (Hook. & Arn.) Torr. & A. Gray
- San Luis Lupine - Lupinus Ludovicianus Greene
- San Luis Mariposa Lily - Calochortus Obispoensis Lemmon
- San Luis Mountain Giant Hyssop - Agastache Mearnsii Wooton & Standl.
- San Luis Mountain Ipomopsis - Ipomopsis Pinnata (Cav.) V.E. Grant
- San Luis Obispo Coyote Mint - Monardella Villosa Benth. ssp. obispoensis (Hoover) Jokerst
- San Luis Obispo Dudleya - Dudleya Abramsii Rose ssp. murina (Eastw.) Moran
- San Luis Obispo Mariposa Lily - Calochortus Simulans (Hoover) Munz
- San Luis Obispo Monardella - Monardella Frutescens (Hoover) Jokerst
- San Luis Obispo Nightshade - Solanum Xanti A. Gray var. obispoense (Eastw.) Wiggins
- San Luis Obispo Sedge - Carex Obispoensis Stacey
- San Luis Obispo Serpentine Dudleya - Dudleya Abramsii Rose ssp. bettinae (Hoover) Bartel
- San Luis Obispo Spineflower - Chorizanthe Breweri S. Watson
- San Luis Obispo Wallflower - Erysimum Capitatum (Douglas ex Hook.) Greene var. lompocense (G. Rossb.) Kartesz
- San Luis Purple Sage - Salvia Leucophylla Greene
- San Luis Yellowcress - Rorippa Coloradensis R. Stuckey
- San Mateo Thorn-mint - Acanthomintha Duttonii (Abrams) Jokerst
- San Mateo Tree Lupine - Lupinus Eximius Burtt Davy
- San Mateo Woolly Sunflower - Eriophyllum Latilobum Rydb.
- San Miguel Calamint - Clinopodium Chandleri (Brandegee) Cantino & S.J. Wagstaff
- San Miguel Island Bedstraw - Galium Californicum Hook. & Arn. ssp. miguelense (Greene) Dempster & Stebbins
- San Miguel Milkvetch - Astragalus Miguelensis Greene
- San Nicholas Biscuitroot - Lomatium Insulare (Eastw.) Munz
- San Nicolas Island Buckwheat - Eriogonum Grande Greene var. timorum Reveal
- San Obispo Milkvetch - Astragalus Didymocarpus Hook. & Arn. var. obispoensis (Rydb.) Jeps.
- San Patricio Tansyaster - Psilactis Heterocarpa (R.L. Hartm. & M.A. Lane) D. Morgan
- San Pedro Daisy - Lasianthaea Podocephala (A. Gray) K. Becker
- San Pedro False Prairie-clover - Marina Calycosa (A. Gray) Barneby
- San Pedro Matchweed - Xanthocephalum Gymnospermoides (A. Gray) Benth. & Hook. f.
- San Pedro River Sandmat - Chamaesyce Trachysperma (Engelm.) Millsp.
- San Pedro Snakeweed - Gutierrezia Petradoria (S.L. Welsh & Goodrich) S.L. Welsh
- San Pedro Ticktrefoil - Desmodium Batocaulon A. Gray
- San Rafael Cryptantha - Cryptantha Jonesiana (Payson) Payson
- San Rafael Milkvetch - Astragalus Rafaelensis M.E. Jones
- San Saba Pinweed - Lechea San-sabeana (Buckley) Hodgdon
- Sanborn's Onion - Allium Sanbornii Alph. Wood
- Sanborn's Onion - Allium Sanbornii Alph. Wood var. sanbornii
- Sanchezia - Sanchezia Ruiz & Pav.
- Sand Bittercress - Cardamine Parviflora L.
- Sand Bittercress - Cardamine Parviflora L. var. arenicola (Britton) O.E. Schulz
- Sand Blackberry - Rubus Cuneifolius Pursh
- Sand Bluestem - Andropogon Hallii Hack.
- Sand Brazos-mint - Brazoria Arenaria Lundell
- Sand Buckwheat - Eriogonum Leptocladon Torr. & A. Gray
- Sand Buckwheat - Eriogonum Leptocladon Torr. & A. Gray var. leptocladon
- Sand Buckwheat - Eriogonum Leptocladon Torr. & A. Gray var. papiliunculi Reveal
- Sand Buckwheat - Eriogonum Leptocladon Torr. & A. Gray var. ramosissimum (Eastw.) Reveal
- Sand Cordgrass - Spartina Bakeri Merr.
- Sand Crabgrass - Digitaria Arenicola (Swallen) Beetle
- Sand Croton - Croton Glandulosus L. var. arenicola (Small) B.W. van Ee, P.E. Berry & S. Ginzbarg
- Sand Dropseed - Sporobolus Cryptandrus (Torr.) A. Gray
- Sand Dune Thistle - Cirsium Pitcheri (Torr. ex Eaton) Torr. & A. Gray
- Sand Fescue - Festuca Ammobia Pavlick
- Sand Fiddleleaf - Nama Carnosum (Wooton) C.L. Hitchc.
- Sand Flax - Linum Arenicola (Small) Winkl.
- Sand Fleabane - Erigeron Arenarioides (D.C. Eaton ex A. Gray) A. Gray ex Rydb.
- Sand Fringepod - Thysanocarpus Curvipes Hook.
- Sand Gilia - Aliciella Leptomeria (A. Gray) J.M. Porter
- Sand Goldenheather - Hudsonia Tomentosa Nutt. var. intermedia Peck
- Sand Goldenrod - Solidago Arenicola B.R. Keener & Kral
- Sand Grape - Vitis Rupestris Scheele
- Sand Heath - Ceratiola Ericoides Michx.
- Sand Hickory - Carya Pallida (Ashe) Engl. & Graebn.
- Sand Jointfir - Ephedra ×arenicola Cutler
- Sand Leek - Allium Scorodoprasum L.
- Sand Leek - Allium Scorodoprasum L. ssp. rotundum (L.) Stearn
- Sand Live Oak - Quercus Geminata Small
- Sand Lovegrass - Eragrostis Trichodes (Nutt.) Alph. Wood
- Sand Lupine - Lupinus Ammophilus Greene
- Sand Milkweed - Asclepias Arenaria Torr.
- Sand Muhly - Muhlenbergia Arenicola Buckley
- Sand Palafox - Palafoxia Hookeriana Torr. & A. Gray
- Sand Palafox - Palafoxia Hookeriana Torr. & A. Gray var. hookeriana
- Sand Palafox - Palafoxia Hookeriana Torr. & A. Gray var. minor Shinners
- Sand Pea - Eriosema (dc.) D. Don
- Sand Penstemon - Penstemon Arenicola A. Nelson
- Sand Phacelia - Phacelia Patuliflora (Engelm. & A. Gray) A. Gray
- Sand Phacelia - Phacelia Patuliflora (Engelm. & A. Gray) A. Gray var. austrotexana J.A. Moyer
- Sand Phacelia - Phacelia Patuliflora (Engelm. & A. Gray) A. Gray var. patuliflora
- Sand Phacelia - Phacelia Patuliflora (Engelm. & A. Gray) A. Gray var. teucriifolia (I.M. Johnst.) Con
- Sand Pine - Pinus Clausa (Chapm. ex Engelm.) Vasey ex Sarg.
- Sand Pink - Dianthus Arenarius L.
- Sand Plain Dwarf Morning-glory - Evolvulus Arenarius R.T. Harms
- Sand Plantain - Plantago Arenaria Waldst. & Kit.
- Sand Post Oak - Quercus Margaretta (Ashe) Small
- Sand Pygmyweed - Crassula Connata (Ruiz & Pav.) A. Berger
- Sand Pygmyweed - Crassula Connata (Ruiz & Pav.) A. Berger var. connata
- Sand Pygmyweed - Crassula Connata (Ruiz & Pav.) A. Berger var. erectoides Bywater & Wickens
- Sand Pygmyweed - Crassula Connata (Ruiz & Pav.) A. Berger var. eremica (Jeps.) Bywater & Wickens
- Sand Pygmyweed - Crassula Connata (Ruiz & Pav.) A. Berger var. subsimplex (S. Watson) Bywater & Wi
- Sand Reverchonia - Reverchonia Arenaria A. Gray
- Sand Rose Gentian - Sabatia Arenicola Greenm.
- Sand Ryegrass - Leymus Arenarius (L.) Hochst.
- Sand Sagebrush - Artemisia Filifolia Torr.
- Sand Sedge - Carex Arenaria L.
- Sand Sedge - Carex Perdentata S.D. Jones
- Sand Spikemoss - Selaginella Arenicola Underw.
- Sand Spikemoss - Selaginella Arenicola Underw. ssp. arenicola
- Sand Spikerush - Eleocharis Montevidensis Kunth
- Sand Springbeauty - Claytonia Arenicola L.F. Hend.
- Sand Ticktrefoil - Desmodium Lineatum DC.
- Sand Timothy - Phleum Arenarium L.
- Sand Verbena - Abronia Juss.
- Sand Violet - Viola Affinis Leconte
- Sand-dune Rockcress - Arabis Media N. Busch
- Sandalwood - Santalum Album L.
- Sandalwood - Santalum L.
- Sandaster - Corethrogyne Dc.
- Sandbar Lovegrass - Eragrostis Frankii C.A. Mey. ex Steud.
- Sandbar Milkvetch - Astragalus Endopterus (Barneby) Barneby
- Sandbar Willow - Salix Interior Rowlee
- Sandberg Birch - Betula ×sandbergii Britton
- Sandberg Bluegrass - Poa Secunda J. Presl
- Sandberg's Biscuitroot - Lomatium Sandbergii (J.M. Coult. & Rose) J.M. Coult. & Rose
- Sandblossoms - Linanthus Parryae (A. Gray) Greene
- Sandbog Deathcamas - Zigadenus Glaberrimus Michx.
- Sandbox Tree - Hura Crepitans L.
- Sandbox Tree - Hura L.
- Sandbur - Cenchrus L.
- Sandcarpet - Cardionema Ramosissimum (Weinm.) A. Nelson & J.F. Macbr.
- Sandcherry - Prunus Pumila L.
- Sanddollar - Astrophytum Asterias (Zucc.) Lem.
- Sanddune Chinchweed - Pectis Glaucescens (Cass.) Keil
- Sanddune Cryptantha - Cryptantha Fendleri (A. Gray) Greene
- Sanddune Ipomopsis - Ipomopsis Gunnisonii (Torr. & A. Gray) V.E. Grant
- Sanddune Linanthus - Linanthus Arenicola (M.E. Jones) Jeps. & V. Bailey
- Sanddune Phacelia - Phacelia Argentea A. Nelson & J.F. Macbr.
- Sanddune Sandbur - Cenchrus Tribuloides L.
- Sanddune Sandmat - Chamaesyce Carunculata (Waterf.) Shinners
- Sanddune Sedge - Carex Pansa L.H. Bailey
- Sanddune Spurge - Euphorbia Trichotoma Kunth
- Sanddune Unicorn-plant - Proboscidea Sabulosa Correll
- Sanddune Wallflower - Erysimum Capitatum (Douglas ex Hook.) Greene
- Sanddune Wallflower - Erysimum Capitatum (Douglas ex Hook.) Greene var. bealianum (Jeps.) G. Rossb.
- Sanddune Wallflower - Erysimum Capitatum (Douglas ex Hook.) Greene var. capitatum
- Sanddune Wallflower - Erysimum Capitatum (Douglas ex Hook.) Greene var. perenne (S. Watson ex Coville) R.
- Sanddwelling Dewberry - Rubus Arenicola Blanch.
- Sanderson's Burrobrush - Hymenoclea Sandersonii (S.L. Welsh) N.H. Holmgren
- Sandfood - Pholisma Sonorae (Torr. ex A. Gray) Yatsk.
- Sandgrass - Mibora Adans.
- Sandgrass - Triplasis P. Beauv.
- Sandhill Amaranth - Amaranthus Arenicola I.M. Johnst.
- Sandhill Goosefoot - Chenopodium Cycloides A. Nelson
- Sandhill Jointweed - Polygonella Fimbriata (Elliott) Horton
- Sandhill Muhly - Muhlenbergia Pungens Thurb.
- Sandhill Oak - Quercus Inopina Ashe
- Sandhill St. Johnswort - Hypericum Lloydii (Svens.) P. Adams
- Sandhill Thistle - Cirsium Repandum Michx.
- Sandhill's Blazing Star - Liatris Cokeri Pyne & Stucky
- Sandhills Lily - Lilium Pyrophilum M.W. Skinner & Sorrie
- Sandhills Milkvetch - Astragalus Michauxii (Kuntze) F.J. Herm.
- Sandia Mountain Alumroot - Heuchera Pulchella Wooton & Standl.
- Sandloving Monkeyflower - Mimulus Arenarius A.L. Grant
- Sandloving Penstemon - Penstemon Ammophilus N.H. Holmgren & L.M. Shultz
- Sandmallow - Sidastrum Baker f.
- Sandmat - Chamaesyce Gray
- Sandmat - Chamaesyce Pergamena (Small) Small
- Sandmat - Chamaesyce ×keyensis Small
- Sandmat Manzanita - Arctostaphylos Pumila Nutt.
- Sandmint - Rhododon Epling
- Sandmyrtle - Leiophyllum Buxifolium (Bergius) Elliott
- Sandoricum Cav.
- Sandoricum Koetjape (Burm. f.) Merr.
- Sandpaper Oak - Quercus Vaseyana Buckley
- Sandpaper Plant - Petalonyx A. Gray
- Sandpaper Vervain - Verbena Scabra Vahl
- Sandparsley - Ammoselinum Torr. & A. Gray
- Sandplain False Foxglove - Agalinis Acuta Pennell
- Sandplain Flax - Linum Intercursum E.P. Bicknell
- Sandpuffs - Tripterocalyx (torr.) Hook.
- Sandreed - Calamovilfa (a. Gray) Hack. ex Scribn. & Southworth
- Sandscrub Ceanothus - Ceanothus Dentatus Torr. & A. Gray
- Sandspurry - Spergularia (pers.) J. Presl & C. Presl
- Sandstede's Reindeer Lichen - Cladina Sandstedei (Abbayes) Ahti
- Sandstede's Wart Lichen - Verrucaria Sandstedei de Lesd.
- Sandstone Milkvetch - Astragalus Sesquiflorus S. Watson
- Sandswamp Whitetop - Rhynchospora Latifolia (Baldw. ex Elliott) W.W. Thomas
- Sandweed - Athysanus Greene
- Sandwich Beach Strawberry - Fragaria Chiloensis (L.) Mill. ssp. sandwicensis (Decne.) Staudt
- Sandwort - Arenaria L.
- Sandwort Cetraria Lichen - Cetraria Arenaria Karnefelt
- Sandwort Daisy Fleabane - Erigeron Bellidiastrum Nutt. var. arenarius (Greene) G.L. Nesom
- Sandwort Drymary - Drymaria Arenarioides Humb. & Bonpl. ex Schult. [excluded]
- Sandwort Homalothecium Moss - Homalothecium Arenarium (Lesq.) E. Lawton
- Sandwort Microcalicium Lichen - Microcalicium Arenarium (Hampe ex A. Massal.) Tibell
- Sandwort - Moehringia L.
- Sandwort Orange Lichen - Caloplaca Arenaria (Pers.) Müll. Arg.
- Sandy Field Hairsedge - Bulbostylis Stenophylla (Elliott) C.B. Clarke
- Sandyfield Beaksedge - Rhynchospora Megalocarpa A. Gray
- Sandyfield Dewberry - Rubus Iniens L.H. Bailey
- Sandyplain Clustervine - Jacquemontia Cayensis Britton
- Sandyseed Clammyweed - Polanisia Dodecandra (L.) DC. ssp. trachysperma (Torr. & A. Gray) Iltis
- Sandysoil Indiangrass - Sorghastrum Setosum (Griseb.) Hitchc.
- Sandysoil Suncup - Camissonia Strigulosa (Fisch. & C.A. Mey.) P.H. Raven
- Sandywoods Chaffhead - Carphephorus Bellidifolius (Michx.) Torr. & A. Gray
- Sandywoods Sedge - Carex Dasycarpa Muhl.
- Sanford's Ocellularia Lichen - Ocellularia Sanfordiana (Zahlbr.) Hale
- Sangre De Cristo - Jatropha Cardiophylla (Torr.) Müll. Arg.
- Sanguinaria - Alternanthera Ficoidea (L.) P. Beauv.
- Sanguinaria Canadensis L. var. rotundifolia (Greene) Fedde
- Sanguine Purple Coneflower - Echinacea Sanguinea Nutt.
- Sanguisorba Agrimonoides Ces.
- Sanguisorba Albanica András. & Jáv.
- Sanguisorba Canadensis L. ssp. latifolia (Hook.) Calder & Roy L. Taylor
- Sanguisorba Canadensis L. var. latifolia Hook.
- Sanguisorba Hybrida (L.) Nordborg
- Sanguisorba Microcephala C. Presl
- Sanguisorba Minor Scop. ssp. magnolii (Spach) Briq.
- Sanguisorba Minor Scop. ssp. muricata (Spach ex Bonnier & Layens) Nordborg
- Sanguisorba Occidentalis Nutt.
- Sanguisorba Officinalis L. ssp. microcephala (C. Presl) Calder & Roy L. Taylor
- Sanguisorba Officinalis L. var. polygama (F. Nyl.) Mela & A. Caj.
- Sanguisorba Sitchensis C.A. Mey.
- Sanguisorba Stipulata Raf.
- Sanguisorba Tenuifolia Fisch. ex Link
- Sanguisorba Tenuifolia Fisch. ex Link var. alba Trautv. & C.A. Mey., nom. nud.
- Sanibel Island Lovegrass - Eragrostis Pectinacea (Michx.) Nees ex Steud. var. tracyi (Hitchc.) P.M. Peterson
- Sanibel Shrubverbena - Lantana Depressa Small var. sanibelensis R.W. Sanders
- Sanicle - Sanicula L.
- Sanicula Bipinnatifida Douglas ex Hook. var. flava Jeps.
- Sanicula Canadensis L. var. floridana (E.P. Bicknell) H. Wolff
- Sanicula Canadensis L. var. typica H. Wolff
- Sanicula Crassicaulis Poepp. ex DC. var. howellii (J.M. Coult. & Rose) Mathias
- Sanicula Floridana E.P. Bicknell
- Sanicula Graveolens Poepp. ex DC. var. septentrionalis (Greene) H. St. John
- Sanicula Gregaria E.P. Bicknell
- Sanicula Haleakalae H. St. John
- Sanicula Lobata (Hillebr. ex H. Wolff) H. St. John
- Sanicula Marilandica L. var. petiolulata Fernald
- Sanicula Nevadensis S. Watson
- Sanicula Nevadensis S. Watson var. septentrionalis (Greene) Mathias
- Sanicula Sandwicensis A. Gray var. lobata Hillebr. ex H. Wolff
- Sanicula Septentrionalis Greene
- Sanicula Simulans Hoover
- Sanicula Tripartita Suksd.
- Sanicula ×howellii (J.M. Coult. & Rose) Shan & Constance
- Sanidophyllum Cumulicola Small
- Sanionia Moss - Sanionia Loeske
- Sanionia Moss - Sanionia Orthothecioides (Lindb.) Loeske
- Sanionia Moss - Sanionia Uncinata (Hedw.) Loeske
- Sanionia Moss - Sanionia Uncinata (Hedw.) Loeske var. uncinata
- Sansevieria Cylindrica Bojer ex Hook. [excluded]
- Sansevieria Fasciata Prain [excluded]
- Sansevieria Longiflora Sims [excluded]
- Sansevieria Metallica Horton ex Gerome & Labroy
- Sansevieria - Sansevieria Thunb.
- Sansevieria Thyrsiflora Thunb.
- Santa Ana Pitchersage - Lepechinia Cardiophylla Epling
- Santa Barbara Bedstraw - Galium Cliftonsmithii (Dempster) Dempster & Stebbins
- Santa Barbara Ceanothus - Ceanothus Impressus Trel.
- Santa Barbara Ceanothus - Ceanothus Impressus Trel. var. impressus
- Santa Barbara Ceanothus - Ceanothus Impressus Trel. var. nipomensis McMinn
- Santa Barbara Honeysuckle - Lonicera Subspicata Hook. & Arn. var. denudata Rehder
- Santa Barbara Island Buckwheat - Eriogonum Giganteum S. Watson var. compactum Dunkle
- Santa Barbara Island Liveforever - Dudleya Traskiae (Rose) Moran
- Santa Barbara Milkvetch - Astragalus Trichopodus (Nutt.) A. Gray
- Santa Barbara Milkvetch - Astragalus Trichopodus (Nutt.) A. Gray var. lonchus (M.E. Jones) Barneby
- Santa Barbara Milkvetch - Astragalus Trichopodus (Nutt.) A. Gray var. phoxus (M.E. Jones) Barneby
- Santa Barbara Milkvetch - Astragalus Trichopodus (Nutt.) A. Gray var. trichopodus
- Santa Barbara Sedge - Carex Barbarae Dewey
- Santa Barbara Spineflower - Chorizanthe Wheeleri S. Watson
- Santa Barbara Wirelettuce - Stephanomeria Elata Nutt.
- Santa Catalina Burstwort - Hermannia Pauciflora S. Watson
- Santa Catalina Figwort - Scrophularia Villosa Pennell
- Santa Catalina Indian Paintbrush - Castilleja Tenuiflora Benth.
- Santa Catalina Island Bedstraw - Galium Catalinense A. Gray
- Santa Catalina Island Bedstraw - Galium Catalinense A. Gray ssp. catalinense
- Santa Catalina Island Desert-thorn - Lycium Hassei Greene
- Santa Catalina Island Manzanita - Arctostaphylos Catalinae P.V. Wells
- Santa Catalina Mariposa Lily - Calochortus Catalinae S. Watson
- Santa Catalina Monkeyflower - Mimulus Traskiae A.L. Grant
- Santa Catalina Mountain Centaury - Centaurium Nudicaule (Engelm.) B.L. Rob.
- Santa Catalina Mountain Phlox - Phlox Tenuifolia E.E. Nelson
- Santa Catalina Mountain Sage - Salvia Amissa Epling
- Santa Catalina Prairie Clover - Dalea Pulchra Gentry
- Santa Clara Thorn-mint - Acanthomintha Lanceolata Curran
- Santa Clara Valley Liveforever - Dudleya Setchellii (Jeps.) Britton & Rose
- Santa Clemente Island Bedstraw - Galium Catalinense A. Gray ssp. acrispum Dempster
- Santa Cruz Beehive Cactus - Coryphantha Recurvata (Engelm.) Britton & Rose
- Santa Cruz Clover - Trifolium Buckwestiorum Isely
- Santa Cruz Cypress - Hesperocyparis Abramsiana (C.B. Wolf) Bartel
- Santa Cruz Cypress - Hesperocyparis Abramsiana (C.B. Wolf) Bartel var. abramsiana
- Santa Cruz Cypress - Hesperocyparis Abramsiana (C.B. Wolf) Bartel var. butanoensis (Silba) Bartel & R.P. Adams
- Santa Cruz Desertdandelion - Malacothrix Squalida Greene
- Santa Cruz Gooseberry - Ribes Thacherianum (Jeps.) Munz
- Santa Cruz Island Buckwheat - Eriogonum Arborescens Greene
- Santa Cruz Island Desertdandelion - Malacothrix Indecora Greene
- Santa Cruz Island Fringepod - Thysanocarpus Conchuliferus Greene
- Santa Cruz Island Hollyfern - Arachniodes Insularis W.H. Wagner
- Santa Cruz Island Liveforever - Dudleya Nesiotica (Moran) Moran
- Santa Cruz Island Manzanita - Arctostaphylos Tomentosa (Pursh) Lindl. ssp. subcordata (Eastw.) P.V. Wells
- Santa Cruz Island Monkeyflower - Mimulus Brandegeei Pennell
- Santa Cruz Island Oak - Quercus Parvula Greene var. parvula
- Santa Cruz Island Silverhosackia - Lotus Argophyllus (A. Gray) Greene var. adsurgens Dunkle
- Santa Cruz Island Silverhosackia - Lotus Argophyllus (A. Gray) Greene var. niveus (Greene) Ottley
- Santa Cruz Island Suncup - Camissonia Hirtella (Greene) P.H. Raven
- Santa Cruz Island Ticktrefoil - Desmodium Psilocarpum A. Gray
- Santa Cruz Island Torrey Pine - Pinus Torreyana Parry ex Carrière ssp. insularis J.R. Haller
- Santa Cruz Island Winged Rockcress - Sibara Filifolia (Greene) Greene
- Santa Cruz Manzanita - Arctostaphylos Andersonii A. Gray
- Santa Cruz Mountains Beardtongue - Penstemon Rattanii A. Gray ssp. kleei (Greene) D.D. Keck
- Santa Cruz Sedge - Carex Saliniformis Mack.
- Santa Cruz Silverpuffs - Microseris Decipiens K.L. Chambers
- Santa Cruz Tarplant - Holocarpha Macradenia (DC.) Greene
- Santa Cruz Wallflower - Erysimum Teretifolium Eastw.
- Santa Cruz Water-lily - Victoria Cruziana A.D. Orb.
- Santa Fe Blazingstar - Mentzelia Springeri (Standl.) Tidestr.
- Santa Fe Milkvetch - Astragalus Feensis M.E. Jones
- Santa Fe Phlox - Phlox Nana Nutt.
- Santa Inez Goldenbanner - Thermopsis Macrophylla Hook. & Arn.
- Santa Lucia Bedstraw - Galium Clementis Eastw.
- Santa Lucia Dwarf Rush - Juncus Luciensis Ertter
- Santa Lucia Horkelia - Horkelia Yadonii Ertter
- Santa Lucia Lupine - Lupinus Cervinus Kellogg
- Santa Lucia Manzanita - Arctostaphylos Luciana P.V. Wells
- Santa Lucia Mint - Pogogyne Clareana J.T. Howell
- Santa Lucia Mountain Bush Monkeyflower - Diplacus Fasciculatus (Pennell) McMinn
- Santa Lucia Phacelia - Phacelia Grisea A. Gray
- Santa Lucia Suncup - Camissonia Luciae P.H. Raven
- Santa Maria Feverfew - Parthenium Hysterophorus L.
- Santa Maria - Vernonia Albicaulis Pers.
- Santa Monica Dust Lichen - Lepraria Santamonicae K. Knudsen & J.A. Elix
- Santa Monica Lecidea Lichen - Lecidea Santae-monicae H. Magn.
- Santa Monica Mountains Dudleya - Dudleya Cymosa (Lem.) Britton & Rose ssp. ovatifolia (Britton) Moran
- Santa Monica Rinodina Lichen - Rinodina Santae-monicae H. Magn.
- Santa Rita Mountain Aster - Symphyotrichum Potosinum (A. Gray) G.L. Nesom
- Santa Rita Mountain Bean - Phaseolus Ritensis M.E. Jones
- Santa Rita Mountain Dodder - Cuscuta Odontolepis Engelm.
- Santa Rita Mountain Draba - Draba Petrophila Greene
- Santa Rita Mountain Draba - Draba Petrophila Greene var. petrophila
- Santa Rita Mountain Draba - Draba Petrophila Greene var. viridis (A. Heller) C.L. Hitchc.
- Santa Rita Mountain Grama - Bouteloua Eludens Griffiths
- Santa Rita Mountain Ticktrefoil - Desmodium Retinens Schltdl.
- Santa Rita Mountain Yellowshow - Amoreuxia Gonzalezii Sprague & Riley
- Santa Rita Pricklypear - Opuntia Santa-rita (Griffiths & Hare) Rose
- Santa Rita Snakeroot - Ageratina Paupercula (A. Gray) R.M. King & H. Rob.
- Santa Rita Threeawn - Aristida Californica Thurb. ex S. Watson var. glabrata Vasey
- Santa Rosa Basalt Brodiaea - Brodiaea Santarosae T.J.Chester, W.P.Armstr. & Madore
- Santa Rosa Horkelia - Horkelia Tenuiloba (Torr.) A. Gray
- Santa Rosa Island Manzanita - Arctostaphylos Confertiflora Eastw.
- Santa Rosa Island Sage - Salvia Brandegeei Munz
- Santa Rosa Mountains Linanthus - Leptosiphon Floribundum (A. Gray) J.M. Porter & L.A. Johnson ssp. hallii (Jeps.) J.M. Po
- Santa Susana Bush Monkeyflower - Diplacus Rutilus (A.L. Grant) McMinn
- Santa Susana Tarweed - Deinandra Minthornii (Jeps.) B.G. Baldw.
- Santalum Ellipticum Gaudich. var. latifolium (A. Gray) Fosberg
- Santalum Ellipticum Gaudich. var. littorale (Hillebr.) Skottsb.
- Santalum Ellipticum Gaudich. var. luteum (Rock) O. Deg.
- Santalum Freycinetianum Gaudich. var. longifolium (Meurisse) O. Deg.
- Santalum Involutum H. St. John
- Santalum Lanaiense (Rock) Rock
- Santalum Majus H. St. John
- Santalum Paniculatum Hook. & Arn. var. chartaceum O. Deg. & I. Deg.
- Santalum Pyrularium A. Gray
- Santalum Pyrularium A. Gray var. sphaerolithos Skottsb.
- Santee Azalea - Rhododendron Eastmanii K.A. Kron & M. Creel
- Santesson's Map Lichen - Rhizocarpon Santessonii Timdal
- Santesson's Thelomma Lichen - Thelomma Santessonii Tibell
- Santesson's Tricharia Lichen - Tricharia Santessonii D. Hawksw.
- Santo Domingo False Willow - Baccharis Myrsinites (Lam.) Pers.
- Santolina Neapolitana Jord. & Fourr.
- Santolina Pincushion - Chaenactis Santolinoides Greene
- Santolina Rosmarinifolia L.
- Santolina Suaveolens Pursh
- Santolina Virens Mill.
- Santonica - Artemisia Cina O. Berg & C.F. Schmidt
- Sanvitalia Angustifolia A. Gray
- Sapello Canyon Larkspur - Delphinium Sapellonis Cockerell
- Sapindus Drummondii Hook. & Arn.
- Sapindus Lonomea H. St. John
- Sapindus Marginatus Willd.
- Sapindus Oahuensis Hillebr. ex Radlk., orth. var.
- Sapindus Thurstonii Rock
- Sapium Aucuparium auct. non Jacq.
- Sapium Biloculare (S. Watson) Pax
- Sapium Caribaeum Urb.
- Sapium Indicum Willd.
- Sapium Jamaicense Sw., nom. illeg.
- Sapium Japonicum (Siebold & Zucc.) Pax & K. Hoffm.
- Sapium Sebiferum (L.) Roxb.
- Sapodilla - Manilkara Zapota (L.) P. Royen
- Saponaria Officinalis L. var. glaberrima Ser.
- Saponaria Porrigens L.
- Saponaria Vaccaria L.
- Sapota Achras Mill.
- Sapota - Sapota Mill.
- Sapote - Casimiroa Llave & Lex.
- Sappanwood - Caesalpinia Sappan L.
- Sapphire Woollystar - Eriastrum Sapphirinum (Eastw.) H. Mason
- Sapphire Woollystar - Eriastrum Sapphirinum (Eastw.) H. Mason ssp. dasyanthum (Brand) H. Mason
- Sapphire Woollystar - Eriastrum Sapphirinum (Eastw.) H. Mason ssp. sapphirinum
- Sapphire-berry - Symplocos Paniculata (Thunb.) Miq.
- Saptree - Garcinia L.
- Saquiyac - Miconia Affinis DC.
- Saracha Antillana Krug & Urb.
- Saracha Procumbens (Cav.) Ruiz & Pav.
- Sarah's Buckwheat - Eriogonum Lachnogynum Torr. ex Benth. var. sarahiae (N.D. Atwood & A. Clifford) Reveal
- Sarawak Bean - Vigna Hosei (Craib) Backer
- Sarcanthopsis Raymundi (Schltr.) J.J. Wood & Ormerod, nom. nud.
- Sarcanthopsis - Sarcanthopsis Garay
- Sarcanthopsis - Sarcanthopsis Nagarensis (Rchb. f.) Garay
- Sarchgyne Lichen - Sarcogyne Clavus (DC.) Krempelh.
- Sarcobatus Vermiculatus (Hook.) Torr. var. baileyi (Coville) Jeps.
- Sarcocornia Ambigua (Michx.) M.A. Alonso & M.B. Crespo
- Sarcocornia Fruticosa (L.) A.J. Scott [excluded]
- Sarcocornia Pacifica (Standl.) A.J. Scott var. utahensis (Tidestr.) Munz
- Sarcographa Intricans (Nyl.) Müll. Arg.
- Sarcographa Lichen - Sarcographa Fée
- Sarcographa Lichen - Sarcographa Labyrinthica (Ach.) Müll. Arg.
- Sarcographa Lichen - Sarcographa Medusulina (Nyl.) Müll. Arg.
- Sarcographa Lichen - Sarcographa Tricosa (Ach.) Müll. Arg.
- Sarcogyne Lichen - Sarcogyne Anthroocarpa H. Magn.
- Sarcogyne Lichen - Sarcogyne Bolleana H. Magn.
- Sarcogyne Lichen - Sarcogyne Flotow
- Sarcogyne Lichen - Sarcogyne Integra (de Lesd.) H. Magn.
- Sarcogyne Lichen - Sarcogyne Oligospora H. Magn.
- Sarcogyne Lichen - Sarcogyne Privigna (Ach.) A. Massal.
- Sarcogyne Lichen - Sarcogyne Regularis Körb.
- Sarcogyne Lichen - Sarcogyne Similis H. Magn.
- Sarcogyne Pruinosa auct.
- Sarcogyne Simplex (Davies) Nyl.
- Sarcolobus - Sarcolobus R. Br.
- Sarcolobus - Sarcolobus Retusus K. Schum.
- Sarcomphalus Domingensis (Spreng.) Krug & Urb.
- Sarcomphalus Reticulatus (Vahl) Urb.
- Sarcomphalus Taylorii Britton
- Sarcopygme Pacifica (Reinecke) Setch. & Christoph.
- Sarcopygme Setch. & Christoph.
- Sarcopyrenia Cylindrospora (Crouan & Crouan) Aguirre
- Sarcopyrenia Nyl.
- Sarcosagium Lichen - Sarcosagium A. Massal.
- Sarcosagium Lichen - Sarcosagium Campestre (Fr.) Poetsch & Schiedem.
- Sarcostemma Clausum (Jacq.) Schult.
- Sarcostemma Crispum Benth.
- Sarcostemma Cynanchoides Decne.
- Sarcostemma Cynanchoides Decne. ssp. hartwegii (Vail) R. Holm
- Sarcostemma Cynanchoides Decne. var. hartwegii (Vail) Shinners
- Sarcostemma Hirtellum (A. Gray) R. Holm
- Sarcostemma Lobata Waterf.
- Sarcostemma Torreyi (A. Gray) Woodson
- Sarea Lichen - Sarea Difformis (Fr.) Fr.
- Sarea Lichen - Sarea Fr.
- Sargent Juniper - Juniperus Chinensis L. var. sargentii A. Henry
- Sargent's Apple - Malus Sargentii Rehder
- Sargent's Barberry - Berberis Sargentiana C.K. Snied.
- Sargent's Catchfly - Silene Sargentii S. Watson
- Sargent's Cypress - Hesperocyparis Sargentii (Jeps.) Bartel
- Sargent's Hawthorn - Crataegus Sargentii Beadle
- Sargentia Aricocca H. Wendl. & Drude
- Saribus Oliviformis Hassk.
- Sarita Rosette Grass - Dichanthelium Nodatum (Hitchc. & Chase) Gould
- Sarmenthypnum Moss - Sarmenthypnum Sarmentosum (Wahlenb.) Tuom. & T. Kop.
- Sarmenthypnum Moss - Sarmenthypnum Tuom. & T. Kop.
- Sarmienta Repens Ruiz & Pav.
- Sarmienta Ruiz & Pav.
- Sarothamnus Scoparius (L.) Wimm. ex Koch
- Sarothra Drummondii Grev. & Hook.
- Sarothra Gentianoides L.
- Sarracenia Alabamensis Case & R.B. Case
- Sarracenia Alabamensis Case & R.B. Case ssp. alabamensis
- Sarracenia Alabamensis Case & R.B. Case ssp. wherryi (D.E. Schnell) Case & R.B. Case
- Sarracenia Alabamensis Case & R.B. Case ssp. wherryi Case & R.B. Case, nom. inval.
- Sarracenia Drummondii Croom
- Sarracenia Heterophylla Eaton
- Sarracenia Jonesii Wherry
- Sarracenia Mooreana Veitch
- Sarracenia Purpurea L. ssp. gibbosa (Raf.) Wherry
- Sarracenia Purpurea L. ssp. heterophylla (Eaton) Torr.
- Sarracenia Purpurea L. ssp. purpurea
- Sarracenia Purpurea L. ssp. purpurea var. montana D.E. Schnell & Determann
- Sarracenia Purpurea L. ssp. purpurea var. purpurea
- Sarracenia Purpurea L. ssp. venosa (Raf.) Wherry
- Sarracenia Purpurea L. var. burkii Schnell
- Sarracenia Purpurea L. var. ripicola B. Boivin
- Sarracenia Purpurea L. var. stolonifera Macfarlane & D.W. Steckbeck
- Sarracenia Purpurea L. var. terrae-novae La Pylaie
- Sarracenia Rubra Walter f. jonesii (Wherry) C.R. Bell
- Sarracenia Rubra Walter ssp. alabamensis (Case & R.B. Case) Schnell, nom. illeg.
- Sarracenia Sledgei Macfarlane
- Sarracenia Variolaris Michx.
- Sarracenia ×mandaiana J.R. Pitcher & W.A. Manda
- Sarsaparilla - Smilax Aristolochiifolia Mill.
- Sarsparilla Vine - Smilax Pumila Walter
- Sartwell's Sedge - Carex Sartwellii Dewey
- Sartwell's Sedge - Carex Sartwellii Dewey var. sartwellii
- Sartwell's Sedge - Carex Sartwellii Dewey var. stenorrhyncha F.J. Herm.
- Sartwellia Gypsophila Powell & B.L. Turner [excluded]
- Sartwellia Puberula Rydb.
- Sarvis Holly - Ilex Amelanchier M.A. Curtis ex Chapm.
- Sasa Japonica (Siebold & Zucc. ex Steud.) Makino
- Sasa Pygmaea (Miq.) E.G. Camus
- Sasa Senanensis (Franch. & Sav.) Rehder
- Sasak's Snow Lichen - Stereocaulon Sasakii Zahlbr.
- Sasak's Snow Lichen - Stereocaulon Sasakii Zahlbr. var. simplex (Riddle) Lamb
- Sasanqua Camellia - Camellia Sasanqua Thunb.
- Saskatoon Serviceberry - Amelanchier Alnifolia (Nutt.) Nutt. ex M. Roem.
- Saskatoon Serviceberry - Amelanchier Alnifolia (Nutt.) Nutt. ex M. Roem. var. alnifolia
- Saskatoon Serviceberry - Amelanchier Alnifolia (Nutt.) Nutt. ex M. Roem. var. humptulipensis (G.N. Jones) C.L.
- Saskatoon Serviceberry - Amelanchier Alnifolia (Nutt.) Nutt. ex M. Roem. var. semiintegrifolia (Hook.) C.L. Hit
- Sassafras Albidum (Nutt.) Nees var. molle (Raf.) Fernald
- Sassafras Officinale Nees & Eberm.
- Sassafras Sassafras (L.) Karst., nom. inval.
- Sassafras - Sassafras Albidum (Nutt.) Nees
- Sassafras - Sassafras Nees & Eberm.
- Sassafras Variifolium (Salisb.) Kuntze
- Sassia Violacea (L.) Holub
- Sasswood - Erythrophleum Afzel. ex R. Br.
- Sasswood - Erythrophleum Suaveolens (Guill. & Perr.) Brenan
- Satincurls - Clematis Catesbyana Pursh
- Satinleaf - Chrysophyllum Oliviforme L.
- Satintail - Imperata Cirillo
- Satiny Milkvetch - Astragalus Magdalenae Greene
- Satiny Willow - Salix Pellita Andersson
- Satureja Acinos (L.) Scheele
- Satureja Arkansana (Nutt.) Briq.
- Satureja Ascendens (Jord.) K. Moly
- Satureja Ashei Weath.
- Satureja Brownei (Sw.) Briq.
- Satureja Calamintha (L.) Scheele
- Satureja Calamintha (L.) Scheele ssp. ascendens (Jord.) Briq.
- Satureja Calamintha (L.) Scheele var. glandulosa (Riquien) Briq.
- Satureja Calamintha (L.) Scheele var. nepeta (L.) Briq.
- Satureja Calamintha (L.) Scheele var. nepetoides (Jord.) Briq.
- Satureja Caroliniana auct. non (Michx.) Briq.
- Satureja Chamissonis (Benth.) Briq.
- Satureja Chandleri (Brandegee) Druce
- Satureja Coccinea (Nutt. ex Hook.) Bertol.
- Satureja Dentata (Chapm.) Briq.
- Satureja Douglasii (Benth.) Briq.
- Satureja Georgiana (Harper) H.E. Ahles
- Satureja Glabella (Michx.) Briq.
- Satureja Glabella (Michx.) Briq. var. angustifolia (Torr.) Svens.
- Satureja Glabra (Nutt.) Fernald
- Satureja Mimuloides (Benth.) Briq.
- Satureja Nepeta (L.) Scheele
- Satureja Rigida W. Bartram ex Benth.
- Satureja Sylvatica (Bromf.) K. Maly ssp. ascendens (Jord.) Roy L. Taylor & MacBryde
- Satureja Vulgaris (L.) Fritsch
- Satureja Vulgaris (L.) Fritsch var. diminuta (Simon) Fernald & Wiegand
- Satureja Vulgaris (L.) Fritsch var. neogaea Fernald
- Saturn Skin Lichen - Leptogium Saturninum (Dicks.) Nyl.
- Saucer-plant - Aeonium Undulatum Webb & Bethel.
- Saucerflower - Antiphytum Dc. & Meisn.
- Sauco - Sambucus Palmensis Link
- Saunders' Widelip Orchid - Liparis Saundersiana Rchb. f.
- Sauropus - Sauropus Blume
- Saururus - Saururus L.
- Sausage Tree - Kigelia Africana (Lam.) Benth.
- Sausage Tree - Kigelia Dc.
- Saussurea Alpina (L.) DC. [excluded]
- Saussurea Angustifolia (Willd.) DC. ssp. yukonensis (A.E. Porsild) Cody
- Saussurea Angustifolia (Willd.) DC. var. viscida (Hultén) S.L. Welsh
- Saussurea Glomerata Poir.
- Saussurea Nuda Ledeb. ssp. densa (Hook.) G.W. Douglas
- Saussurea Nuda Ledeb. var. densa (Hook.) Hultén
- Saussurea - Saussurea Amara (L.) DC.
- Saussurea - Saussurea Amara (L.) DC. var. glomerata (Poir.) Trautv.
- Saussurea Tilesii (Ledeb.) Ledeb. [excluded]
- Saussurea Viscida Hultén var. yukonensis (A.E. Porsild) Hultén
- Sauteria Alpina (Nees) Nees
- Sauteria Nees
- Sauvagesia - Sauvagesia L.
- Savanna Blazing Star - Liatris Savannensis Kral & G.L. Nesom
- Savanna Iris - Iris Hexagona Walter var. savannarum (Small) R.C. Foster
- Savannah Aster - Eurybia Chapmanii (Torr. & A. Gray) G.L. Nesom
- Savannah Beaksedge - Rhynchospora Debilis Gale
- Savannah Dewberry - Rubus Ictus L.H. Bailey
- Savannah False Pimpernel - Lindernia Grandiflora Nutt.
- Savannah Fanpetals - Sida Aggregata C. Presl
- Savannah Iris - Iris Tridentata Pursh
- Savannah Meadowbeauty - Rhexia Alifanus Walter
- Savannah Milkweed - Asclepias Pedicellata Walter
- Savannah Panicgrass - Panicum Stenodes Griseb.
- Savannah Primrose-willow - Ludwigia Virgata Michx.
- Savannah Sneezeweed - Helenium Vernale Walter
- Savannah Yelloweyed Grass - Xyris Flabelliformis Chapm.
- Savannah-panicgrass - Phanopyrum (raf.) Nash
- Savannah-panicgrass - Phanopyrum Gymnocarpon (Elliott) Nash
- Savastana Alpina (Sw. ex Willd.) Scribn.
- Savastana Nashii E.P. Bicknell
- Savastana Odorata (L.) Scribn.
- Savastana Pauciflora (R. Br.) Scribn. & Merr.
- Savia Arida Warnock & M.C. Johnst.
- Savia Clusiifolia Griseb., nom. utique rej.
- Savia Phyllanthoides (Nutt.) Pax & K. Hoffm.
- Savia - Savia Willd.
- Savicz's Snow Lichen - Stereocaulon Saviczii Du Rietz
- Savin - Juniperus Sabina L.
- Savinleaf Groundpine - Lycopodium Sabinifolium Willd.
- Savory - Satureja L.
- Saw Greenbrier - Smilax Bona-nox L.
- Saw Greenbrier - Smilax Bona-nox L. var. bona-nox
- Saw Palmetto - Serenoa Repens (W. Bartram) Small
- Saw Phacelia - Phacelia Serrata J. Voss
- Saw-wort - Saussurea Dc.
- Saw-wort - Saussurea ×tschuktschorum Lipsch. (pro sp.)
- Sawara-cypress - Chamaecyparis Pisifera Siebold & Zucc.
- Sawblade - Dyckia Brevifolia Baker
- Sawgrass - Cladium P. Br.
- Sawleaf Buckthorn - Rhamnus Serrata Humb. & Bonpl. ex Schult.
- Sawleaf Bush Penstemon - Penstemon Fruticosus (Pursh) Greene var. serratus (D.D. Keck) Cronquist
- Sawsedge - Gahnia J.r. Forst. & G. Forst.
- Sawsedge - Morelotia Gaudich.
- Sawsepal Penstemon - Penstemon Glaber Pursh
- Sawsepal Penstemon - Penstemon Glaber Pursh var. glaber
- Sawtooth Blackberry - Rubus Argutus Link
- Sawtooth Bristleweed - Hazardia Squarrosa (Hook. & Arn.) Greene var. grindelioides (DC.) W.D. Clark
- Sawtooth Bristleweed - Hazardia Squarrosa (Hook. & Arn.) Greene var. obtusa (Greene) Jeps.
- Sawtooth Candyleaf - Stevia Serrata Cav.
- Sawtooth Filmy Fern - Hymenophyllum Serrulatum (C. Presl) C. Chr.
- Sawtooth Goldenbush - Hazardia Squarrosa (Hook. & Arn.) Greene
- Sawtooth Goldenbush - Hazardia Squarrosa (Hook. & Arn.) Greene var. squarrosa
- Sawtooth Hawthorn - Crataegus Viburnifolia Sarg.
- Sawtooth Lewisia - Lewisia Serrata Heckard & Stebbins
- Sawtooth Logwood - Xylosma Crenata (H. St. John) H. St. John
- Sawtooth Oak - Quercus Acutissima Carruthers
- Sawtooth Sage - Salvia Subincisa Benth.
- Sawtooth Sandmat - Chamaesyce Serrula (Engelm.) Wooton & Standl.
- Sawtooth Sunflower - Helianthus Grosseserratus M. Martens
- Sawtooth Wormwood - Artemisia Serrata Nutt.
- Saxegothaea Lindl.
- Saxen's Sedge - Carex ×saxenii Raymond
- Saxifraga Adscendens L. var. oregonensis (Raf.) Breitung
- Saxifraga Aequidentata (Small) Rosend.
- Saxifraga Aestivalis Fisch. & C.A. Mey.
- Saxifraga Aestivalis auct. non Fisch. & C.A. Mey. p.p.
- Saxifraga Aizoon Jacq. ssp. neogaea (Butters) Á. Löve & D. Löve
- Saxifraga Aizoon Jacq. var. neogaea Butters
- Saxifraga Amplexifolia Sternb.
- Saxifraga Arguta auct. non D. Don
- Saxifraga Austrina (A. Nelson) A. Nelson
- Saxifraga Austromontana Wiegand
- Saxifraga Bracteata D. Don
- Saxifraga Bracteosa Suksd.
- Saxifraga Bracteosa Suksd. var. angustifolia Suksd.
- Saxifraga Bracteosa Suksd. var. micropetala Suksd.
- Saxifraga Bronchialis L. var. austromontana (Wiegand) Piper ex G.N. Jones
- Saxifraga Bronchialis L. var. cherlerioides (D. Don) Engl.
- Saxifraga Bronchialis L. var. purpureomaculata Hultén
- Saxifraga Bronchialis L. var. vespertina (Small) Rosend.
- Saxifraga Caespitosa L. ssp. eucaespitosa Engl. & Irmsch.
- Saxifraga Caespitosa L. var. emarginata (Small) Rosend.
- Saxifraga Caespitosa L. var. lemmonii Engl. & Irmsch.
- Saxifraga Caespitosa L. var. minima Blank.
- Saxifraga Caespitosa L. var. subgemmifera (Engl. & Irmsch.) C.L. Hitchc.
- Saxifraga Calycina Sternb. ssp. calycina Sternb. [excluded]
- Saxifraga Calycina Sternb. ssp. unalaschcensis (Sternb.) Hultén
- Saxifraga Cernua L. var. exilioides Polunin
- Saxifraga Cespitosa L. ssp. cespitosa L., orth. var.
- Saxifraga Cespitosa L. ssp. delicatula (Small) A.E. Porsild, orth. var.
- Saxifraga Cespitosa L. ssp. eucaespitosa Engl. & Irmsch., orth. var.
- Saxifraga Cespitosa L. ssp. monticola (Small) A.E. Porsild, orth. var.
- Saxifraga Cespitosa L. ssp. sileneflora (Sternb. ex Cham.) Hultén, orth. var.
- Saxifraga Cespitosa L. ssp. subgemmifera Engl. & Irmsch., orth. var.
- Saxifraga Cespitosa L. ssp. uniflora (R. Br.) A.E. Porsild, orth. var.
- Saxifraga Cespitosa L. var. lemmonii Engl. & Irmsch., orth. var.
- Saxifraga Cespitosa L. var. minima Blank., orth. var.
- Saxifraga Cespitosa L. var. subgemmifera (Engl. & Irmsch.) C.L. Hitchc., orth. var.
- Saxifraga Cespitosa L., orth. var.
- Saxifraga Cherlerioides D. Don
- Saxifraga Claytoniifolia Canby ex Small
- Saxifraga Codyanus Zhmylev
- Saxifraga Columbiana Piper
- Saxifraga Columbiana Piper var. apetala (Piper) Engl. & Irmsch.
- Saxifraga Crandallii Gandog.
- Saxifraga Crenatifolia (Small) Fedde
- Saxifraga Davurica Willd. ssp. grandipetala (Engl. & Irmsch.) Hultén
- Saxifraga Davurica Willd. var. grandipetala (Engl. & Irmsch.) B. Boivin
- Saxifraga Davurica Willd. var. unalaschcensis (Sternb.) Engl.
- Saxifraga Debilis Engelm. ex A. Gray
- Saxifraga Exilis Stephan
- Saxifraga Fallax Greene
- Saxifraga Ferruginea Graham var. foliacea A.M. Johnson
- Saxifraga Ferruginea Graham var. macounii Engl. & Irmsch.
- Saxifraga Firma Litv. ex Losinsk.
- Saxifraga Flagellaris Willd. ex Sternb. ssp. platysepala (Trautv.) A.E. Porsild
- Saxifraga Flagellaris Willd. ex Sternb. var. crandallii (Gandog.) Dorn
- Saxifraga Flagellaris Willd. ex Sternb. var. platysepala Trautv.
- Saxifraga Foliolosa R. Br. var. multiflora Hultén
- Saxifraga Forbesii Vasey
- Saxifraga Fragarioides Greene
- Saxifraga Fragosa Suksd. ex Small
- Saxifraga Fragosa Suksd. ex Small ssp. claytoniifolia (Canby ex Small) Bacig.
- Saxifraga Fragosa Suksd. ex Small var. leucandra Suksd.
- Saxifraga Funstonii (Small) Fedde
- Saxifraga Gracillima A.M. Johnson
- Saxifraga Greenei Blank.
- Saxifraga Hallii A. Gray
- Saxifraga Hieraciifolia Waldst. & Kit. ex Willd. var. rydbergii (Small) Engl. & Irmsch.
- Saxifraga Hirculus L. ssp. coloradensis K.O. Hedb.
- Saxifraga Hirculus L. var. propinqua (R. Br.) Simmons
- Saxifraga Hirsuta L. [excluded]
- Saxifraga Hyperborea R. Br. ssp. debilis (Engelm. ex A. Gray) Á. Löve & D. Löve & Kap
- Saxifraga Insularis (Hultén) Hultén
- Saxifraga Integrifolia Hook. var. apetala (Piper) M.E. Jones
- Saxifraga Integrifolia Hook. var. claytoniifolia (Canby ex Small) Rosend.
- Saxifraga Integrifolia Hook. var. columbiana (Piper) C.L. Hitchc.
- Saxifraga Integrifolia Hook. var. leptopetala (Suksd.) Engl. & Irmsch.
- Saxifraga Integrifolia Hook. var. micropetala (Suksd.) Engl. & Irmsch.
- Saxifraga Integrifolia Hook. var. rhomboidea (Greene) M.E. Jones
- Saxifraga Jamesii Torr.
- Saxifraga Klickitatensis A.M. Johnson
- Saxifraga Laevicarpa A.M. Johnson
- Saxifraga Laevicaulis A.M. Johnson
- Saxifraga Lyallii Engl. var. hultenii Calder & Savile
- Saxifraga Lyallii Engl. var. laxa Engl.
- Saxifraga Marshallii Greene ssp. idahoensis (Piper) Krause & Beamish
- Saxifraga Marshallii Greene var. idahoensis (Piper) Engl. & Irmsch.
- Saxifraga Mertensiana Bong. var. eastwoodiae (Small) Engl. & Irmsch.
- Saxifraga Micropetala (Small) Fedde
- Saxifraga Montana (Small) Fedde
- Saxifraga Montanensis Small
- Saxifraga Montanensis Small var. subpetala (E.E. Nelson) Engl. & Irmsch.
- Saxifraga Monticola (Small) Á. Löve & D. Löve
- Saxifraga Napensis Small
- Saxifraga Nivalis L. var. gaspensis (Fernald) B. Boivin
- Saxifraga Nivalis L. var. rufopilosa Hultén
- Saxifraga Nivalis L. var. tenuis Wahlenb.
- Saxifraga Occidentalis S. Watson ssp. rufidula (Small) Bacig.
- Saxifraga Occidentalis S. Watson var. aequidentata (Small) M. Peck
- Saxifraga Occidentalis S. Watson var. allenii (Small) C.L. Hitchc.
- Saxifraga Occidentalis S. Watson var. dentata (Engl. & Irmsch.) C.L. Hitchc.
- Saxifraga Occidentalis S. Watson var. idahoensis (Piper) C.L. Hitchc.
- Saxifraga Occidentalis S. Watson var. latipetiolata C.L. Hitchc.
- Saxifraga Occidentalis S. Watson var. rufidula (Small) C.L. Hitchc.
- Saxifraga Occidentalis S. Watson var. wallowensis M. Peck
- Saxifraga Oppositifolia L. var. nathorstii Dusén
- Saxifraga Oregana Howell var. montanensis (Small) C.L. Hitchc.
- Saxifraga Oregana Howell var. sierrae Coville
- Saxifraga Oregana Howell var. subpetala (E.E. Nelson) C.L. Hitchc.
- Saxifraga Parvifolia Greene
- Saxifraga Pectinata Pursh, non Schott, Nyman & Kotschy
- Saxifraga Peltata Torr. ex Benth.
- Saxifraga Pensylvanica L. ssp. interior Burns
- Saxifraga Pensylvanica L. ssp. tenuirostrata Burns
- Saxifraga Pensylvanica L. var. forbesii (Vasey) Engl. & Irmsch.
- Saxifraga Pensylvanica L. var. purpuripetala (A.M. Johnson) Bush
- Saxifraga Plantaginea Small
- Saxifraga Porsildiana (Calder & Savile) Jurtzev & V.V. Petrovsky
- Saxifraga Prorepens Fisch. ex Sternb.
- Saxifraga Punctata L. p.p.
- Saxifraga Punctata L. ssp. arguta auct. non (D. Don) Hultén
- Saxifraga Punctata L. ssp. carlottae Calder & Savile
- Saxifraga Punctata L. ssp. cascadensis Calder & Savile
- Saxifraga Punctata L. ssp. insularis Hultén
- Saxifraga Punctata L. ssp. nelsoniana (D. Don) Hultén
- Saxifraga Punctata L. ssp. pacifica Hultén
- Saxifraga Punctata L. ssp. porsildiana Calder & Savile
- Saxifraga Punctata L. var. arguta sensu Engl. & Irmsch.
- Saxifraga Punctata L. var. carlottae (Calder & Savile) B. Boivin
- Saxifraga Punctata L. var. cascadensis (Calder & Savile) B. Boivin
- Saxifraga Punctata L. var. nelsoniana (D. Don) Macoun
- Saxifraga Punctata L. var. porsildiana (Calder & Savile) B. Boivin
- Saxifraga Pyrolifolia D. Don
- Saxifraga Radiata Small
- Saxifraga Reevesii Cory
- Saxifraga Reflexa Hook. ssp. occidentalis (S. Watson) Hultén
- Saxifraga Rhomboidea Greene var. austrina A. Nelson
- Saxifraga Rhomboidea Greene var. franciscana (Small) Kearney & Peebles
- Saxifraga Richardsonii Hook.
- Saxifraga Rivularis L. ssp. flexuosa (Sternb.) Gjaerev.
- Saxifraga Rivularis L. var. debilis (Engelm. ex A. Gray) Dorn
- Saxifraga Rivularis L. var. flexuosa (Sternb.) Engl. & Irmsch.
- Saxifraga Rivularis L. var. hyperborea (R. Br.) Dorn
- Saxifraga Rivularis L. var. laurentiana (Ser.) Engl.
- Saxifraga Rydbergii Small
- Saxifraga Sarmentosa L.
- Saxifraga Serpyllifolia Pursh ssp. chrysantha (A. Gray) W.A. Weber
- Saxifraga Serpyllifolia Pursh var. chrysantha (A. Gray) Dorn
- Saxifraga Serpyllifolia Pursh var. purpurea Hultén
- Saxifraga Setigera Pursh
- Saxifraga Sileneflora Sternb. ex Cham.
- Saxifraga Stellaris L. var. comosa Poir.
- Saxifraga Sullivantii Torr. & A. Gray
- Saxifraga Tolmiei Torr. & A. Gray var. ledifolia (Greene) Engl. & Irmsch.
- Saxifraga Umbellulata sensu Greene, non Hook. f. & Thomson
- Saxifraga Unalaschcensis Sternb.
- Saxifraga Vespertina (Small) Fedde
- Saxifraga Virginiensis Michx. var. californica (Greene) Jeps.
- Saxifraga Vreelandii (Small) Fedde ex Just
- Saxifraga ×geum L. (pro sp.) [excluded]
- Saxifrage Pink - Petrorhagia Saxifraga (L.) Link
- Saxifrage - Saxifraga Calycina Sternb.
- Saxifrage - Saxifraga L.
- Saxifrage - Saxifraga Stellaris L.
- Saxifragopsis - Saxifragopsis Small
- Scabiosa Arvensis L.
- Scabiosa Australis Wulfen
- Scabiosa - Knautia L.
- Scabiosa Succisa L.
- Scabland Fleabane - Erigeron Bloomeri A. Gray
- Scabland Fleabane - Erigeron Bloomeri A. Gray var. bloomeri
- Scabland Fleabane - Erigeron Bloomeri A. Gray var. nudatus (A. Gray) Cronquist
- Scabland Fleabane - Erigeron Bloomeri A. Gray var. pubens D.D. Keck
- Scabland Penstemon - Penstemon Deustus Douglas ex Lindl.
- Scabland Penstemon - Penstemon Deustus Douglas ex Lindl. var. deustus
- Scabland Penstemon - Penstemon Deustus Douglas ex Lindl. var. pedicellatus M.E. Jones
- Scabland Penstemon - Penstemon Deustus Douglas ex Lindl. var. suffrutescens L.F. Hend.
- Scabland Penstemon - Penstemon Deustus Douglas ex Lindl. var. variabilis (Suksd.) Cronquist
- Scabland Sagebrush - Artemisia Rigida (Nutt.) A. Gray
- Scadden Flat Checkerbloom - Sidalcea Stipularis J.T. Howell & True
- Scadoxus Multiflorus (Martyn) Raf.
- Scadoxus - Scadoxus Raf.
- Scaevola Chamissoniana Gaudich. var. bracteosa Hillebr.
- Scaevola Chamissoniana Gaudich. var. caerulescens Levl.
- Scaevola Chamissoniana Gaudich. var. cylindrocarpa (Hillebr.) Krause
- Scaevola Chamissoniana Gaudich. var. hitchcockii Skottsb.
- Scaevola Chamissoniana Gaudich. var. piccoi O. Deg. & I. Deg.
- Scaevola Frutescens K. Krause, nom. illeg.
- Scaevola Gaudichaudiana Cham. var. dentata Krause
- Scaevola Gaudichaudiana Cham. var. pilosa Krause
- Scaevola Gaudichaudiana Cham. var. stenolithos Skottsb.
- Scaevola Kauaiensis (O. Deg.) H. St. John
- Scaevola Kilaueae O. Deg. var. powersii O. Deg. & I. Deg.
- Scaevola Procera Hillebr. var. pseudomollis Skottsb.
- Scaevola Skottsbergii H. St. John
- Scaevola Taccada (Gaertn.) Roxb.
- Scaevola Taccada (Gaertn.) Roxb. var. bryanii H. St. John
- Scaevola Taccada (Gaertn.) Roxb. var. fauriei (Levl.) H. St. John
- Scaevola Taccada (Gaertn.) Roxb. var. sericea (Vahl) H. St. John
- Scaldweed - Cuscuta Gronovii Willd. ex Schult.
- Scaldweed - Cuscuta Gronovii Willd. ex Schult. var. calyptrata Engelm.
- Scaldweed - Cuscuta Gronovii Willd. ex Schult. var. gronovii
- Scale Edge Bristle Fern - Trichomanes Membranaceum L.
- Scalebud - Anisocoma Acaulis Torr. & A. Gray
- Scaled Cloak Fern - Notholaena Aschenborniana Klotzsch
- Scaleflower Dodder - Cuscuta Squamata Engelm.
- Scaleleaf Aster - Symphyotrichum Adnatum (Nutt.) G.L. Nesom
- Scaleleaf False Foxglove - Agalinis Aphylla (Nutt.) Raf.
- Scaleseed - Spermolepis Raf.
- Scallion Grass - Eleocharis Mutata (L.) Roem. & Schult.
- Scalloped Laceleaf - Anthurium Crenatum (L.) Kunth
- Scalloped Milkwort - Polygala Crenata C.W. James
- Scalloped Moonwort - Botrychium Crenulatum W.H. Wagner
- Scallopleaf Sage - Salvia Vaseyi (Porter) Parish
- Scaly Blazing Star - Liatris Squarrosa (L.) Michx.
- Scaly Blazing Star - Liatris Squarrosa (L.) Michx. var. compacta Torr. & A. Gray
- Scaly Blazing Star - Liatris Squarrosa (L.) Michx. var. glabrata (Rydb.) Gaiser
- Scaly Blazing Star - Liatris Squarrosa (L.) Michx. var. hirsuta (Rydb.) Gaiser
- Scaly Blazing Star - Liatris Squarrosa (L.) Michx. var. squarrosa
- Scaly Dwarf Polypody - Grammitis Cultrata (Willd.) Proctor
- Scaly Globemallow - Sphaeralcea Leptophylla (A. Gray) Rydb.
- Scaly Polypody - Pleopeltis Humb. & Bonpl. ex Willd.
- Scaly Swordfern - Nephrolepis Hirsutula (J.R. Forst.) C. Presl
- Scalystem - Elytraria Michx.
- Scamman's Oxytrope - Oxytropis Scammaniana Hultén
- Scamman's Springbeauty - Claytonia Scammaniana Hultén
- Scammony - Convolvulus Scammonia L.
- Scandix Cerefolium L.
- Scandix - Scandix L.
- Scapania (dumort.) Dumort., nom. cons.
- Scapania Aequiloba (Schwägr.) Dumort.
- Scapania Americana Müll. Frib.
- Scapania Apiculata Spruce
- Scapania Bolanderi Austin
- Scapania Brevicaulis Taylor
- Scapania Calcicola (Arnell & J. Perss.) Ingham
- Scapania Calcicola (Arnell & J. Perss.) Ingham ssp. calcicola
- Scapania Calcicola (Arnell & J. Perss.) Ingham ssp. ligulifolia (R.M. Schust.) Dams
- Scapania Calciphila R.M. Schust.
- Scapania Carinthiaca J.B. Jack ex Lindb.
- Scapania Compacta (Roth) Dumort.
- Scapania Crassiretis Bryhn
- Scapania Curta (Mart.) Dumort.
- Scapania Curta (Mart.) Dumort. var. curta
- Scapania Curta (Mart.) Dumort. var. grandiretis R.M. Schust.
- Scapania Curta (Mart.) Dumort. var. isoloba R.M. Schust.
- Scapania Cuspiduligera (Nees) Müll. Frib.
- Scapania Cuspiduligera (Nees) Müll. Frib. var. cuspiduligera
- Scapania Cuspiduligera (Nees) Müll. Frib. var. diplophyllopsis R.M. Schust.
- Scapania Degenii Schiffn. ex Müll. Frib.
- Scapania Degenii Schiffn. ex Müll. Frib. var. degenii
- Scapania Degenii Schiffn. ex Müll. Frib. var. dubia R.M. Schust.
- Scapania Glaucocephala (Taylor) Austin
- Scapania Gymnostomophila Kaal.
- Scapania Hians Steph. ex Müll. Frib.
- Scapania Hyperborea Jörg.
- Scapania Invisa R.M. Schust.
- Scapania Irrigua (Nees) Gottsche & Lindenb. & Nees
- Scapania Irrigua (Nees) Gottsche & Lindenb. & Nees ssp. irrigua
- Scapania Irrigua (Nees) Gottsche & Lindenb. & Nees ssp. rufescens (Loeske) R.M. S
- Scapania Kaurinii Ryan
- Scapania Lingulata H. Buch
- Scapania Lingulata H. Buch var. lingulata
- Scapania Lingulata H. Buch var. microphylla (Warnst.) R.M. Schust.
- Scapania Massalongi (Müll. Frib.) Müll. Frib.
- Scapania Mucronata H. Buch
- Scapania Mucronata H. Buch ssp. mucronata
- Scapania Mucronata H. Buch ssp. praetervisa (Meyl.) R.M. Schust.
- Scapania Mucronata H. Buch ssp. praetervisa (Meyl.) R.M. Schust. var. polaris R.M.
- Scapania Mucronata H. Buch ssp. praetervisa (Meyl.) R.M. Schust. var. praetervisa (
- Scapania Nemorea (L.) Grolle
- Scapania Obcordata (Berggr.) S.W. Arnell
- Scapania Obscura (Arnell & C.E.O. Jensen) Schiffn.
- Scapania Ornithopodioides (With.) Pearson
- Scapania Paludicola Loeske & Müll. Frib.
- Scapania Paludicola Loeske & Müll. Frib. var. paludicola
- Scapania Paludicola Loeske & Müll. Frib. var. rotundiloba R.M. Schust.
- Scapania Paludicola Loeske & Müll. Frib. var. viridigemma R.M. Schust.
- Scapania Paludosa (Müll. Frib.) Müll. Frib.
- Scapania Paradoxa R.M. Schust.
- Scapania Paradoxa R.M. Schust. var. paradoxa
- Scapania Paradoxa R.M. Schust. var. ramosa R.M. Schust.
- Scapania Parvifolia Warnst.
- Scapania Perssonii R.M. Schust.
- Scapania Pseudocalcicola R.M. Schust.
- Scapania Pulcherrima R.M. Schust.
- Scapania Saxicola R.M. Schust.
- Scapania Scandica (Arnell & H. Buch) Macvicar
- Scapania Scandica (Arnell & H. Buch) Macvicar var. argutedentata H. Buch
- Scapania Scandica (Arnell & H. Buch) Macvicar var. dimorpha R.M. Schust.
- Scapania Scandica (Arnell & H. Buch) Macvicar var. scandica
- Scapania Serrulata R.M. Schust.
- Scapania Simmonsii Bryhn & Kaal.
- Scapania Spitzbergensis (Lindb.) Müll. Frib.
- Scapania Subalpina (Nees) Dumort.
- Scapania Tundrae (Arnell) H. Buch
- Scapania Uliginosa (Sw. ex Lindenb.) Dumort.
- Scapania Umbrosa (Schrad.) Dumort.
- Scapania Undulata (L.) Dumort.
- Scapania Undulata (L.) Dumort. var. aequatiformis De Not.
- Scapania Undulata (L.) Dumort. var. oakesii (Austin) H. Buch
- Scapania Undulata (L.) Dumort. var. undulata
- Scapania Zemliae S.W. Arnell
- Scaphyglottis - Scaphyglottis Poepp. & Endl.
- Scareweed - Baptisia Simplicifolia Croom
- Scarlet Banana - Musa Coccinea Andrews
- Scarlet Beardtongue - Penstemon Murrayanus Hook.
- Scarlet Beebalm - Monarda Didyma L.
- Scarlet Beeblossom - Oenothera Suffrutescens (Ser.) W.L. Wagner & Hoch
- Scarlet Begonia - Begonia Coccinea Hook.
- Scarlet Bottlebrush - Callistemon Rugulosus (D.F.K. Schltdl. ex Link) DC.
- Scarlet Buckwheat - Eriogonum Phoeniceum L.M. Shultz
- Scarlet Bugler - Penstemon Centranthifolius (Benth.) Benth.
- Scarlet Calamint - Clinopodium Coccineum (Nutt. ex Hook.) Kuntze
- Scarlet Cinquefoil - Potentilla Thurberi A. Gray
- Scarlet Cinquefoil - Potentilla Thurberi A. Gray var. atrorubens (Rydb.) Kearney & Peebles
- Scarlet Cinquefoil - Potentilla Thurberi A. Gray var. sanguinea (Rydb.) Kearney & Peebles
- Scarlet Cinquefoil - Potentilla Thurberi A. Gray var. thurberi
- Scarlet Firethorn - Pyracantha Coccinea M. Roem.
- Scarlet Four O'clock - Mirabilis Coccinea (Torr.) Benth. & Hook. f.
- Scarlet Fritillary - Fritillaria Recurva Benth.
- Scarlet Geranium - Pelargonium Inquinans (L.) L'Hér. ex Aiton
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. aggregata
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. attenuata (A. Gray) V.E. Grant & A.D. Gr
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. bridgesii (A. Gray) V.E. Grant & A.D. Gr
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. candida (Rydb.) V.E. Grant & A.D. Grant
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. collina (Greene) Wilken & Allred
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. formosissima (Greene) Wherry
- Scarlet Gilia - Ipomopsis Aggregata (Pursh) V.E. Grant ssp. weberi V.E. Grant & Wilken
- Scarlet Globemallow - Sphaeralcea Coccinea (Nutt.) Rydb.
- Scarlet Globemallow - Sphaeralcea Coccinea (Nutt.) Rydb. ssp. coccinea
- Scarlet Globemallow - Sphaeralcea Coccinea (Nutt.) Rydb. ssp. elata (Baker f.) Kearney
- Scarlet Hawthorn - Crataegus Pedicellata Sarg.
- Scarlet Hedgehog Cactus - Echinocereus Coccineus Engelm.
- Scarlet Hedgehog Cactus - Echinocereus Coccineus Engelm. var. coccineus
- Scarlet Hedgehog Cactus - Echinocereus Coccineus Engelm. var. paucispinus (Engelm.) D.J. Ferguson
- Scarlet Hedgenettle - Stachys Coccinea Ortega
- Scarlet Indian Paintbrush - Castilleja Coccinea (L.) Spreng.
- Scarlet Jungleflame - Ixora Coccinea L.
- Scarlet Keckiella - Keckiella Ternata (Torr. ex A. Gray) Straw
- Scarlet Keckiella - Keckiella Ternata (Torr. ex A. Gray) Straw ssp. septentrionalis (Munz & I.M. Johns
- Scarlet Keckiella - Keckiella Ternata (Torr. ex A. Gray) Straw ssp. ternata
- Scarlet Lady's Tresses - Dichromanthus Cinnabarinus (Llave & Lex.) Garay
- Scarlet Larkspur - Delphinium Cardinale Hook.
- Scarlet Leather Flower - Clematis Texensis Buckley
- Scarlet Milkvetch - Astragalus Coccineus Brandegee
- Scarlet Monkeyflower - Mimulus Cardinalis Douglas ex Benth.
- Scarlet Oak - Quercus Coccinea Münchh.
- Scarlet Oak - Quercus Coccinea Münchh. var. coccinea
- Scarlet Oak - Quercus Coccinea Münchh. var. tuberculata Sarg.
- Scarlet Passionflower - Passiflora Coccinea Aubl.
- Scarlet Pimpernel - Anagallis Arvensis L.
- Scarlet Pimpernel - Anagallis Arvensis L. ssp. arvensis
- Scarlet Rosemallow - Hibiscus Coccineus Walter
- Scarlet Runner - Phaseolus Coccineus L.
- Scarlet Sage - Salvia Splendens Sellow ex Roem. & Schult.
- Scarlet Spiderling - Boerhavia Coccinea Mill.
- Scarlet Spiral-ginger - Costus Woodsonii Maas
- Scarlet Tasselflower - Emilia Coccinea (Sims) G. Don
- Scarlet Vetch - Vicia Fulgens Battand.
- Scarlet-plume - Euphorbia Fulgens Karw. ex Klotzsch
- Scarletbush - Hamelia Patens Jacq.
- Scarletcreeper - Ipomoea Hederifolia L.
- Scarletfruit Passionflower - Passiflora Foetida L. var. hispida (DC. ex Triana & Planch.) Killip
- Scarletfruit Passionflower - Passiflora Foetida L. var. isthmia Killip
- Scarletfruit Passionflower - Passiflora Foetida L. var. lanuginosa Killip
- Scatter Knotweed - Polygonum Douglasii Greene ssp. spergulariiforme (Meisn. ex Small) J.C. Hickman
- Scattered Paspalum - Paspalum Conspersum Schrad.
- Scentbottle - Platanthera Dilatata (Pursh) Lindl. ex Beck
- Scentbottle - Platanthera Dilatata (Pursh) Lindl. ex Beck var. albiflora (Cham.) Ledeb.
- Scentbottle - Platanthera Dilatata (Pursh) Lindl. ex Beck var. dilatata
- Scented Beardtongue - Penstemon Palmeri A. Gray var. eglandulosus (D.D. Keck) N.H. Holmgren
- Scented Beardtongue - Penstemon Palmeri A. Gray var. macranthus (Eastw.) N.H. Holmgren
- Scented Blacktorch - Erithalis Odorifer Jacq.
- Scented Croton - Croton Suaveolens Torr.
- Scented Cryptantha - Cryptantha Utahensis (A. Gray) Greene
- Scented Oakfern - Gymnocarpium Robertianum (Hoffm.) Newman
- Scented Pussytoes - Antennaria Aromatica Evert
- Scented Senna - Senna Artemisioides (Gaudich. ex DC.) Randell ssp. ×coriacea (Benth.) Randell
- Scented Shootingstar - Dodecatheon Redolens (H.M. Hall) H.J. Thomp.
- Scentless Bayberry - Morella Inodora (W. Bartram) Small
- Scentless False Mayweed - Tripleurospermum Perforatum (Mérat) M. Lainz
- Scentless Geranium - Pelargonium Inodorum Willd.
- Scentless Mock Orange - Philadelphus Inodorus L.
- Scentless Vanilla - Vanilla Inodora Schiede
- Scepterbearing Fleabane - Erigeron Sceptrifer G.L. Nesom
- Sceptridium Biternatum (Savigny) Lyon
- Sceptridium Dissectum (Spreng.) Lyon
- Sceptridium Jenmanii (Underw.) Lyon
- Sceptridium Lunarioides (Michx.) Holub
- Sceptridium Multifidum (S.G. Gmel.) M. Nishida ex Tagawa
- Sceptridium Oneidense (Gilbert) Holub
- Sceptridium Silaifolium (C. Presl) Lyon
- Schaack's Barley - ×elyhordeum Schaackianum (Bowden) Bowden
- Schadonia Lichen - Schadonia Körb.
- Schaefferia - Schaefferia Jacq.
- Schaerer's Disc Lichen - Buellia Schaereri De Not.
- Schaerer's Orange Lichen - Caloplaca Schaereri (Flörke) Zahlbr.
- Schaerer's Psorotichia Lichen - Psorotichia Schaereri (A. Massal.) Arnold
- Schaereria Corticola Muhr & Tønsberg
- Schaereria Lichen - Schaereria Cinereorufa (Schaerer) Th. Fr.
- Schaereria Lichen - Schaereria Endocyanea (Stirt.) Hertel & Gotth. Schneid.
- Schaereria Lichen - Schaereria Fuscocinerea (Nyl.) Clauzade & Roux
- Schaereria Lichen - Schaereria Th. Fr.
- Schaereria Tenebrosa (Flotow) Hertel & Poelt
- Schaffner's Bahia - Bahia Schaffneri S. Watson
- Schaffner's Grasswort - Lilaeopsis Schaffneriana (Schltdl.) J.M. Coult. & Rose
- Schaffner's Grasswort - Lilaeopsis Schaffneriana (Schltdl.) J.M. Coult. & Rose var. recurva (A.W. Hill) Affolter
- Schaffner's Hairsedge - Bulbostylis Schaffneri (Boeckeler) C.B. Clarke
- Schaffner's Spikerush - Eleocharis Schaffneri Boeckeler
- Schaffner's Wattle - Vachellia Schaffneri (S. Watson) Seigler & Ebinger [excluded]
- Schaueria Linearifolia Torr.
- Schaueria Parvifolia Torr.
- Schedonorus Phoenix (Scop.) Holub
- Schedonorus ×festucaceus (Link) Kartesz, ined., database artifact
- Scheel Creek Beardtongue - Penstemon Rhizomatosus N.H. Holmgren
- Scheer's Beehive Cactus - Coryphantha Robustispina (Schott ex Engelm.) Britton & Rose ssp. scheeri (Muehlenpf.) N.P
- Scheer's Beehive Cactus - Coryphantha Robustispina (Schott ex Engelm.) Britton & Rose ssp. uncinata (L.D. Benson) N
- Scheer's Fishhook Cactus - Ancistrocactus Scheeri (Salm-Dyck) Britton & Rose
- Schefflera Odorata (Blanco) Merr. & Rolfe
- Schefflera - Schefflera J.r. Forst. & G. Forst.
- Schell Creek Draba - Draba Pennellii Rollins
- Schenkia Spicata (L.) G. Mans.
- Scheuchzeria Americana (Fernald) G.N. Jones
- Scheuchzeria Palustris L. var. americana Fernald
- Schied's Flax - Linum Schiedeanum Schltdl. & Cham.
- Schied's Snakeherb - Dyschoriste Schiedeana (Nees) Kuntze
- Schied's Snakeherb - Dyschoriste Schiedeana (Nees) Kuntze var. cinerascens Henrickson & Hilsenb.
- Schiede's Sedge - Carex Muriculata F.J. Herm.
- Schiedea Diffusa A. Gray var. angustifolia Wawra
- Schiedea Diffusa A. Gray var. macraei Sherff
- Schiedea Globosa H. Mann var. foliosior O. Deg. & Sherff
- Schiedea Globosa H. Mann var. graminifolia O. Deg. & Sherff
- Schiedea Hookeri A. Gray var. acrisepala Sherff
- Schiedea Hookeri A. Gray var. intercedens Sherff
- Schiedea Kaalae Wawra var. acutifolia Sherff
- Schiedea Laui W.L. Wagner & Weller
- Schiedea Ligustrina Cham. & Schltdl. var. nematopoda O. Deg. & Sherff
- Schiedea Lychnoides Hillebr.
- Schiedea Lydgatei Hillebr. var. attenuata O. Deg. & Sherff
- Schiedea Menziesii Hook. var. forbesii Sherff
- Schiedea Menziesii Hook. var. lihauensis H. St. John
- Schiedea Menziesii Hook. var. spergulacea Hillebr.
- Schiedea Nuttallii Hook. var. intermedia Hillebr.
- Schiedea Nuttallii Hook. var. lihuensis Sherff
- Schiedea Nuttallii Hook. var. molokaiensis Sherff
- Schiedea Nuttallii Hook. var. pauciflora O. Deg. & Sherff
- Schiedea Obovata (Sherff) W.L. Wagner & Weller
- Schiedea Pubescens Hillebr. var. degeneri Sherff
- Schiedea Pubescens Hillebr. var. hillebrandii Sherff
- Schiedea Pubescens Hillebr. var. lanaiensis Sherff
- Schiedea Pubescens Hillebr. var. purpurascens Sherff
- Schiedea Remyi H. Mann
- Schiedea Remyi H. Mann var. foliosa Sherff
- Schiedea Remyi H. Mann var. multinervia Sherff
- Schiedea - Schiedea Cham. & Schltdl.
- Schiedea Spergulina A. Gray var. degeneriana Sherff
- Schiedea Spergulina A. Gray var. major Sherff
- Schiedea Stellarioides H. Mann var. brevifolia Sherff
- Schiedea Stellarioides H. Mann var. hillebrandii Hochr.
- Schiedea Stellarioides H. Mann var. implexoides Sherff
- Schiedea Stellarioides H. Mann var. longifolia Sherff
- Schiedea Trinervis (H. Mann) Pax & K. Hoffm.
- Schiedea Viscosa H. Mann
- Schiedea Viscosa H. Mann var. laevis (Sherff) H. St. John
- Schiedeella Fauci-sanguinea auct. non (D. Dod) Burns-Balogh
- Schiedeella Parasitica auct. non (A. Rich. & Galeotti) Schltr.
- Schiffner's Panicgrass - Panicum Schiffneri Hack.
- Schimper's Acaulon Moss - Acaulon Schimperianum (Sull.) Sull.
- Schimper's Campylopus Moss - Campylopus Schimperi Milde
- Schimper's Ditrichum Moss - Ditrichum Schimperi (Lesq.) Kuntze
- Schinopsis Lorentzii (Griseb.) Engl.
- Schinopsis - Schinopsis Engl.
- Schinopsis - Schinopsis Haenkeana Engl.
- Schinus Terebinthifolia Raddi, orth. var.
- Schinus Terebinthifolius Raddi var. rhoifolius (Mart.) Engl. [excluded]
- Schinz's Pepperweed - Lepidium Schinzii Thell.
- Schisandra Coccinea Michx.
- Schisandra - Schisandra Michx.
- Schismatomma Abietinum (Humb.) A. Massal.
- Schismatomma Californicum (Tuck.) Zahlbr.
- Schismatomma Cupressum Herre
- Schismatomma Glaucescens (Nyl. ex Willey) R.C. Harris
- Schismatomma Hypothallinum (Zahlbr.) Hasse
- Schismatomma Lichen - Schismatomma Flotow & Körb. ex A. Massal.
- Schismatomma Lichen - Schismatomma Pluriloculare Zahlbr.
- Schismatomma Lichen - Schismatomma Rediunta (Hasse) Tehler
- Schismatomma Lichen - Schismatomma Vernans (Tuck.) Zahlbr.
- Schismatomma Ocellatum (Nyl.) Zahlbr.
- Schismatomma Palidellum auct.
- Schismatomma Pericleum (Ach.) Branth & Rostrup
- Schismatomma Ravenelii (Tuck.) Zahlbr.
- Schismatomma Subattigens (Nyl.) Zahlbr.
- Schismus Calycinus (Loefl.) K. Koch
- Schist Cynodontium Moss - Cynodontium Schisti (F. Weber & D. Mohr) Lindb.
- Schistidium Alpicola (Hedw.) Limpr. var. dupretii (Thér.) H.A. Crum
- Schistidium Alpicola (Hedw.) Limpr. var. latifolia (J.E. Zetterst.) Limpr.
- Schistidium Alpicola (Hedw.) Limpr. var. rivulare (Brid.) Limpr.
- Schistidium Alpicola (Hedw.) Limpr., nom. utique rej.
- Schistidium Alpicola auct. non (Hedw.) Limpr.
- Schistidium Ambiguum Sull.
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. ambiguum (Sull.) G. Jones
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. atrofuscum (Schimp.) C.E.O. Jensen
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. brunnescens (Limpr.) Herz.
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. confertum (Funck) H. Möller
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. dupretii (Thér.) Wijk & Margad.
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. gracile (Röhl.) Bruch & Schimp.
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. nigrescens (Molendo) Loeske
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. pulvinatum (Hedw.) C.E.O. Jensen
- Schistidium Apocarpum (Hedw.) Bruch & Schimp. var. strictum (Turner) Moore
- Schistidium Atrofuscum (Schimp.) Limpr.
- Schistidium Brunnescens Limpr.
- Schistidium Gracile (Röhl.) Schleich. ex Limpr.
- Schistidium Holmenianum Steere & Brass.
- Schistidium Moss - Schistidium Andreaeopsis (Müll. Hal.) Laz.
- Schistidium Moss - Schistidium Apocarpum (Hedw.) Bruch & Schimp.
- Schistidium Moss - Schistidium Brid.
- Schistidium Moss - Schistidium Cinclidodonteum (Müll. Hal.) Bremer
- Schistidium Moss - Schistidium Cryptocarpum Nog. & Blum
- Schistidium Moss - Schistidium Heterophyllum (Kindb.) T.T. McIntosh
- Schistidium Moss - Schistidium Tenerum (J.E. Zetterst.) Nyholm
- Schistidium Moss - Schistidium Trichodon (Brid.) Poelt
- Schistidium Platyphyllum (Mitt.) Kindb.
- Schistidium Rivulare (Brid.) Podp. ssp. latifolium (J.E. Zetterst.) Bremer
- Schistidium Strictum (Turner) T. Kop. & Isov.
- Schistidium Tenerrimum (Renauld & Cardot) G. Roth
- Schistidium Teretinerve (Limpr.) Limpr.
- Schistophragma - Schistophragma Benth. ex Endl.
- Schistostega Moss - Schistostega D. Mohr
- Schistostega Moss - Schistostega Pennata (Hedw.) F. Weber & D. Mohr.
- Schizachne Purpurascens (Torr.) Swallen var. pubescens Dore
- Schizachne Stricta (Michx.) Hultén
- Schizachyrium Domingense (Spreng. ex Schult.) Nash
- Schizachyrium Feense (Fourn.) A. Camus
- Schizachyrium Gracile (Spreng.) Nash
- Schizachyrium Hirtiflorum Nees
- Schizachyrium Microstachyum (Desv. ex Ham.) Roseng. et al.
- Schizachyrium Pachyarthron C.A. Gardner
- Schizachyrium Praematurum (Fernald) C.F. Reed
- Schizachyrium Sanguineum (Retz.) Alston var. brevipedicellatum (Beal) Hatch
- Schizachyrium Sanguineum (Retz.) Alston var. oligostachyum (Chapm.) Hatch
- Schizachyrium Scoparium (Michx.) Nash ssp. divergens (Hack.) Gandhi & Smeins
- Schizachyrium Scoparium (Michx.) Nash ssp. littorale (Nash) Gandhi & Smeins
- Schizachyrium Scoparium (Michx.) Nash ssp. neomexicanum (Nash) Gandhi & Smeins
- Schizachyrium Scoparium (Michx.) Nash var. frequens (F.T. Hubbard) Gould
- Schizachyrium Scoparium (Michx.) Nash var. littorale (Nash) Gould
- Schizachyrium Scoparium (Michx.) Nash var. neomexicanum (Nash) Gould
- Schizachyrium Scoparium (Michx.) Nash var. polycladum (Scribn. & C.R. Ball) C.F. Reed
- Schizachyrium Scoparium (Michx.) Nash var. virile (Shinners) Gould
- Schizachyrium Semiberbe Nees
- Schizachyrium Sericatum (Swallen) Gould
- Schizachyrium Stoloniferum Nash
- Schizachyrium Stoloniferum Nash var. wolfei DeSelm
- Schizaea Dichotoma (L.) Sm.
- Schizaea Dichotoma (L.) Sm. var. sellingii Fosberg
- Schizaea Digitata (L.) Sw.
- Schizaea Elegans auct. non (Vahl) Sw.
- Schizaea Germanii (Fée) Prantl
- Schizanthus - Schizanthus Ruiz & Pav.
- Schizococcus Sensitivus (Jeps.) Eastw.
- Schizolegnia Walkerae (Hook.) Alston
- Schizomitrium Pallidum (Hornsch.) H.A. Crum & L.E. Anderson
- Schizonotus Sorbifolius (L.) Lindl.
- Schizopelte Californica Th. Fr.
- Schizopelte Th. Fr.
- Schizophragma Hydrangeoides Siebold & Zucc. [excluded]
- Schizophragma Siebold & Zucc.
- Schizostege Lydgatei (Baker) Hillebr.
- Schkuhria Multiflora Hook. & Arn. var. multiflora
- Schkuhria Pinnata (Lam.) Kuntze ex Thell. var. wislizeni (A. Gray) B.L. Turner
- Schkuhria Wislizeni A. Gray
- Schkuhria Wislizeni A. Gray var. frustrata S.F. Blake
- Schkuhria Wislizeni A. Gray var. wrightii (A. Gray) S.F. Blake
- Schlegelia Portoricensis (Urb.) Britton
- Schlegelia - Schlegelia Miq.
- Schleicher's Bryum Moss - Bryum Schleicheri Schwägr.
- Schleicher's Cracked Lichen - Acarospora Schleicheri (Ach.) A. Massal.
- Schleicher's Entodon Moss - Entodon Schleicheri (Schimp.) Demeter
- Schleichera - Schleichera Willd.
- Schlotheimia Moss - Schlotheimia Brid.
- Schlotheimia Sullivantii Müll. Hal.
- Schlumbergera Gaertneri (Regel) Britton & Rose
- Schlumbergera - Schlumbergera Lem.
- Schmaltzia Anisophylla Greene
- Schmaltzia Crenata (Mill.) Greene
- Schmaltzia Racemulosa Greene
- Schmaltzia Trilobata (Nutt.) Small
- Schmaltzia Trilobata (Nutt.) Small var. anisophylla (Greene) F.A. Barkley
- Schmidelia Occidentalis Sw.
- Schmidt's Xanthoparmelia Lichen - Xanthoparmelia Schmidtii Hale
- Schmidtia Moench
- Schmidtia Pappophoroides Steud. ex J.A. Schmidt
- Schmoll's Milkvetch - Astragalus Schmolliae Ced. Porter
- Schneck Oak - Quercus Shumardii Buckley var. schneckii (Britton) Sarg.
- Schobera Angiosperma (Murray) Britton
- Schoberia Occidentalis S. Watson
- Schoenocrambe Suffrutescens (Rollins) S.L. Welsh & Chatterley
- Schoenolirion Album Durand
- Schoenolirion Bracteosum (S. Watson) Jeps.
- Schoenolirion Elliottii Feay ex A. Gray
- Schoenolirion Texanum (Scheele) A. Gray
- Schoenoplectus Erectus (Poir.) Palla ex Raynal
- Schoenoplectus Erectus (Poir.) Palla ex Raynal ssp. raynalii (Schuyler) Lye
- Schoenoplectus Fluviatilis (Torr.) M.T. Strong
- Schoenoplectus Glaucus (Lam.) Kartesz
- Schoenoplectus Hallii (A. Gray) S.G. Sm.
- Schoenoplectus Juncoides (Roxb.) Palla
- Schoenoplectus Juncoides (Roxb.) Palla ssp. purshianus (Fernald) Soják
- Schoenoplectus Lacustris (L.) Palla ssp. acutus (Muhl. ex Bigelow) Á. Löve & D. Löve
- Schoenoplectus Lacustris (L.) Palla ssp. creber (Fernald) Á. Löve & D. Löve
- Schoenoplectus Lacustris (L.) Palla ssp. tabernaemontani (C.C. Gmel.) Á. Löve & D. Löve
- Schoenoplectus Lacustris (L.) Palla ssp. validus (Vahl) T. Koyama
- Schoenoplectus Litoralis auct. non (Schrad.) Palla
- Schoenoplectus Maritimus (L.) Lye
- Schoenoplectus Mucronatus (L.) Palla
- Schoenoplectus Novae-angliae (Britton) M.T. Strong
- Schoenoplectus Pungens (Vahl) Palla var. polyphyllus (Boeckeler) Dorn
- Schoenoplectus Purshianus (Fernald) M.T. Strong
- Schoenoplectus Robustus (Pursh) M.T. Strong
- Schoenoplectus Rubiginosus (Beetle) Soják p.p.
- Schoenoplectus Saximontanus (Fernald) Raynal
- Schoenoplectus Setaceus (L.) Palla
- Schoenoplectus Smithii (A. Gray) Soják
- Schoenoplectus Validus (Vahl) Á. Löve & D. Löve
- Schoenoplectus Validus (Vahl) Á. Löve & D. Löve ssp. creber (Fernald) Á. Löve & D. Löve
- Schoenoplectus Validus (Vahl) Á. Löve & D. Löve ssp. luxurians (Miq.) Soják
- Schoenoplectus ×oblongatus (T. Koyama) Soják, database artifact
- Schoenoplectus ×scheuchzeri (Bruegger) Palla ex Janchen, nom. inval.
- Schoenoprasum Lineare Kunth
- Schoenus Coloratus L.
- Schoenus Fascicularis Michx.
- Schoenus Ferrugineus L. [excluded]
- Schoenus Miliaceus Lam.
- Schoenus Punctatus R. Br.
- Schoenus Rariflorus Michx.
- Schoenus Rugosus Vahl
- Schoepfia Chrysophylloides (A. Rich.) Planch.
- Schoepfia - Schoepfia Schreb.
- Schofield's Andreaea Moss - Andreaea Schofieldiana B.M. Murray
- Schofield's Ctenidium Moss - Ctenidium Schofieldii Nish.
- Schofield's Sphagnum - Sphagnum Schofieldii H.A. Crum
- Schofieldia J.d. Godfrey
- Schofieldia Monticola J.D. Godfrey
- Scholander's Asahinea Lichen - Asahinea Scholanderi (Llano) W.L. Culb. & C.F. Culb.
- Scholander's Beard Lichen - Usnea Scholanderi Llano
- Scholander's Navel Lichen - Umbilicaria Scholanderi (Llano) Krog
- Schomburgk's Mimosa - Mimosa Schomburgkii Benth.
- Schoolcraft's Dewberry - Rubus Schoolcraftianus L.H. Bailey
- Schott's Calico - Loeseliastrum Schottii (Torr.) Timbrook
- Schott's Century Plant - Agave Schottii Engelm.
- Schott's Century Plant - Agave Schottii Engelm. var. schottii
- Schott's Dalea - Psorothamnus Schottii (Torr.) Barneby
- Schott's Pygmycedar - Peucephyllum Schottii A. Gray
- Schott's Sedge - Carex Schottii Dewey
- Schott's Stickpea - Zapoteca Formosa (Kunth) H.M. Hern.
- Schott's Stickpea - Zapoteca Formosa (Kunth) H.M. Hern. var. schottii (Torr. ex S. Watson) H.M. Hern.
- Schott's Wattle - Vachellia Schottii (Torr.) Seigler & Ebinger
- Schott's Wirelettuce - Stephanomeria Schottii A. Gray
- Schott's Yellowhood - Nissolia Schottii (Torr.) A. Gray
- Schott's Yucca - Yucca ×schottii Engelm. (pro sp.)
- Schradera - Schradera Vahl
- Schradera Vahlii Steyerm.
- Schrankia Angustata Torr. & A. Gray
- Schrankia Floridana Chapm.
- Schrankia Hystricina (Small ex Britton & Rose) Standl.
- Schrankia Latidens (Small) K. Schum.
- Schrankia Leptocarpa DC.
- Schrankia Microphylla (Dryand.) J.F. Macbr.
- Schrankia Microphylla (Dryand.) J.F. Macbr. var. floridana (Chapm.) Isely
- Schrankia Nuttallii (DC. ex Britton & Rose) Standl.
- Schrankia Nuttallii (DC. ex Britton & Rose) Standl. var. hystricina (Small ex Britto
- Schrankia Nuttallii (DC. ex Britton & Rose) Standl. var. hystricina (Small ex Britto
- Schrankia Occidentalis (Wooton & Standl.) Standl.
- Schrankia Portoricensis Urb.
- Schrankia Roemeriana (Scheele) Blank.
- Schrankia Uncinata Willd.
- Schreber's Aster - Eurybia Schreberi (Nees) Nees
- Schreber's Big Red Stem Moss - Pleurozium Schreberi (Brid.) Mitt.
- Schreber's Dicranella Moss - Dicranella Schreberiana (Hedw.) Hilf. ex H.A. Crum & L.E. Anderson
- Schreber's Dicranella Moss - Dicranella Schreberiana (Hedw.) Hilf. ex H.A. Crum & L.E. Anderson var. schreberiana
- Schreber's Pondweed - Potamogeton ×schreberi Fisch.
- Schreiber's Manzanita - Arctostaphylos Glutinosa Schreib.
- Schuette's Hawthorn - Crataegus Schuettei Ashe
- Schultes' Bedstraw - Galium Schultesii Vest
- Schwalbea Americana L. var. australis (Pennell) Reveal & Broome
- Schwalbea Australis Pennell
- Schwalbea - Schwalbea L.
- Schwaneck's Logwood - Xylosma Schwaneckeana (Krug & Urb.) Urb.
- Schwarz's Campylopus Moss - Campylopus Schwarzii Schimp.
- Schweinfurth's Olive - Canarium Schweinfurthii Engl.
- Schweinitz's Dotted Lichen - Bacidia Schweinitzii (Fr. ex E. Michener) A. Schneid.
- Schweinitz's Flatsedge - Cyperus Schweinitzii Torr.
- Schweinitz's Ragwort - Packera Schweinitziana (Nutt.) W.A. Weber & Á. Löve
- Schweinitz's Sedge - Carex Schweinitzii Dewey ex Schwein.
- Schweinitz's Sunflower - Helianthus Schweinitzii Torr. & A. Gray
- Schweinitz's Waterweed - Elodea Schweinitzii (Planch.) Caspary
- Schwerin's False Indigo - Amorpha Schwerinii C.K. Schneid.
- Schwetschkeopsis Denticulata (Sull.) Broth.
- Schwetschkeopsis Moss - Schwetschkeopsis Broth.
- Schwetschkeopsis Moss - Schwetschkeopsis Fabronia (Schwägr.) Broth.
- Sciacassia Siamea (Lam.) Britton ex Britton & Rose
- Sciaphila Blume
- Sciaphila Stemmermanniae Fosberg & Sachet
- Sciaromium Fryei R.S. Williams
- Sciaromium Lescurii (Sull.) Broth.
- Scilla Biflora L. [excluded]
- Scilla Hispanica Mill.
- Scilla Luciliae (Boiss.) Speta
- Scilla Nonscripta (L.) Hoffmanns. & Link
- Scilla Peruviana L.
- Scilla - Scilla L.
- Scilla Verna Huds.
- Scindapsus Aureus (Lindl. & André) Engl.
- Scirpodendron Ghaeri Merrill
- Scirpodendron Zipp. ex Kurz
- Scirpus Acutus Muhl. ex Bigelow
- Scirpus Acutus Muhl. ex Bigelow var. occidentalis (S. Watson) Beetle
- Scirpus Aestivalis Retz.
- Scirpus Americanus Pers.
- Scirpus Americanus Pers. var. longispicatus Britton
- Scirpus Americanus Pers. var. monophyllus (J. Presl & C. Presl) T. Koyama
- Scirpus Americanus Pers. var. polyphyllus (Boeckeler) Beetle
- Scirpus Americanus auct. non Pers.
- Scirpus Annuus All.
- Scirpus Atropurpureus Retz.
- Scirpus Atrovirens Willd. var. flaccidifolius Fernald
- Scirpus Atrovirens Willd. var. georgianus (Harper) Fernald
- Scirpus Atrovirens Willd. var. pallidus Britton
- Scirpus Autumnalis L.
- Scirpus Barbatus Rottb.
- Scirpus Bergsonii Schuyler
- Scirpus Caespitosus L. var. austriacus (Pall.) Asch. & Graebn., orth. var.
- Scirpus Caespitosus L. var. callosus Bigelow, orth. var.
- Scirpus Caespitosus L. var. delicatulus Fernald, orth. var.
- Scirpus Caespitosus L., orth. var.
- Scirpus Californicus (C.A. Mey.) Steud.
- Scirpus Californicus (C.A. Mey.) Steud. var. tereticulmis (Steud.) Beetle
- Scirpus Campestris Britton
- Scirpus Capillaris L.
- Scirpus Caribaea Rottb.
- Scirpus Carinatus (Hook. & Arn. ex Torr.) A. Gray, non Sm.
- Scirpus Carolinianus Lam.
- Scirpus Castaneus Michx.
- Scirpus Cernuus Vahl p.p.
- Scirpus Cernuus Vahl ssp. californicus (Torr.) Thorne
- Scirpus Cernuus Vahl var. californicus (Torr.) Beetle
- Scirpus Cespitosus L.
- Scirpus Cespitosus L. var. austriacus (Pall.) Asch. & Graebn.
- Scirpus Cespitosus L. var. callosus Bigelow
- Scirpus Cespitosus L. var. delicatulus Fernald
- Scirpus Chilensis Nees & Meyen ex Kunth
- Scirpus Ciliatifolius Elliott
- Scirpus Clementis M.E. Jones
- Scirpus Clintonii A. Gray
- Scirpus Coarctatus Elliott
- Scirpus Complanatus Retz.
- Scirpus Confervoides Poir.
- Scirpus Conglomeratus Kunth
- Scirpus Corymbosus L.
- Scirpus Criniger A. Gray
- Scirpus Cubensis Poepp. & Kunth
- Scirpus Cylindricus (Torr.) Britton
- Scirpus Cyperinus (L.) Kunth var. brachypodus (Fernald) Gilly
- Scirpus Cyperinus (L.) Kunth var. condensatus Fernald
- Scirpus Cyperinus (L.) Kunth var. eriophorum (Michx.) Kunth
- Scirpus Cyperinus (L.) Kunth var. laxus (A. Gray) Beetle
- Scirpus Cyperinus (L.) Kunth var. pedicellatus (Fernald) Schuyler
- Scirpus Cyperinus (L.) Kunth var. pelius Fernald
- Scirpus Cyperinus (L.) Kunth var. rubricosus (Fernald) Gilly
- Scirpus Debilis Pursh, non Lam.
- Scirpus Deltarum Schuyler
- Scirpus Dichotomus L.
- Scirpus Equisetoides Elliott
- Scirpus Erectus Poir.
- Scirpus Eriophorum Michx.
- Scirpus Erismaniae Schuyler
- Scirpus Etuberculatus (Steud.) Kunze
- Scirpus Fernaldii E.P. Bicknell
- Scirpus Ferrugineus L.
- Scirpus Fistulosus Poir., non Forssk., nom. illeg.
- Scirpus Flavescens Poir.
- Scirpus Fluitans L.
- Scirpus Fluviatilis (Torr.) A. Gray
- Scirpus Fontinalis Harper
- Scirpus Fuirenus T. Koyama
- Scirpus Geniculata L.
- Scirpus Glaucus Lam.
- Scirpus Glaucus Torr., nom. inq.
- Scirpus Hallii A. Gray
- Scirpus Heterochaetus Chase
- Scirpus Holoschoenus L.
- Scirpus Hotarui auct. non Ohwi
- Scirpus Hudsonianus (Michx.) Fernald
- Scirpus Hystrix Thunb.
- Scirpus Interstinctus Vahl
- Scirpus Juncoides Roxb.
- Scirpus Juncoides Roxb. var. digynus (Boeckeler) T. Koyama
- Scirpus Juncoides Roxb. var. williamsii (Fernald) T. Koyama
- Scirpus Kamtschaticus C.A. Mey.
- Scirpus Koilolepis (Steud.) Gleason
- Scirpus Lacustris L. p.p.
- Scirpus Lacustris L. ssp. creber (Fernald) T. Koyama
- Scirpus Lacustris L. ssp. glaucus (Rchb.) Hartm.
- Scirpus Lacustris L. ssp. tabernaemontani (C.C. Gmel.) Syme
- Scirpus Lacustris L. ssp. validus (Vahl) T. Koyama
- Scirpus Lacustris L. var. tenuiculmis Sheldon
- Scirpus Lacustris auct. non L.
- Scirpus Lineatus auct. non Michx.
- Scirpus Lithospermus L.
- Scirpus Litoralis (Phil.) Kuntze, nom. illeg.
- Scirpus Litoralis Schrad.
- Scirpus Litoralis Schrad. var. capensis (Boeckeler) T. Koyama
- Scirpus Littoralis Schrad. C79827var. capensis (Boeckeler) T. Koyama
- Scirpus Littoralis Schrad., orth. var.
- Scirpus Luzulae auct. non L.
- Scirpus Mamillata Lindb. f.
- Scirpus Maritimus L.
- Scirpus Maritimus L. var. agonus (Fernald) Beetle
- Scirpus Maritimus L. var. fernaldii (E.P. Bicknell) Beetle
- Scirpus Maritimus L. var. fluviatilis Torr.
- Scirpus Maritimus L. var. macrostachyus Michx.
- Scirpus Maritimus L. var. paludosus (A. Nelson) Kük.
- Scirpus Maritimus L. var. tuberosus auct. non (Desf.) Roem. & Schult.
- Scirpus Micranthus Vahl
- Scirpus Micranthus Vahl var. drummondii (Nees) Mohlenbr.
- Scirpus Micranthus Vahl var. minor (Schrad. ex Roem. & Schult.) B. Boivin
- Scirpus Microcarpus J. Presl & C. Presl var. longispicatus M. Peck
- Scirpus Microcarpus J. Presl & C. Presl var. rubrotinctus (Fernald) M.E. Jones
- Scirpus Miliaceus L., nom. utique rej.
- Scirpus Molestus M.C. Johnst.
- Scirpus Monophyllus J. Presl & C. Presl
- Scirpus Montana Kunth
- Scirpus Mucronatus L.
- Scirpus Mutatus L.
- Scirpus Nanus Spreng.
- Scirpus Nanus Spreng. var. anachaetus (Torr.) Britton
- Scirpus Novae-angliae Britton
- Scirpus Obtusus Willd.
- Scirpus Occidentalis (S. Watson) Chase
- Scirpus Olneyi A. Gray
- Scirpus Ovatus Roth
- Scirpus Pachystylus C. Wright
- Scirpus Pacificus Britton
- Scirpus Paludosus A. Nelson
- Scirpus Paludosus A. Nelson var. atlanticus Fernald
- Scirpus Palustris L.
- Scirpus Pauciflorus Lightf.
- Scirpus Pedicellatus Fernald var. pullus Fernald
- Scirpus Planifolius Muhl., non Grimm, nom. illeg.
- Scirpus Prolifer Rottb.
- Scirpus Puberulus Michx.
- Scirpus Pumilus Vahl
- Scirpus Pumilus Vahl ssp. rollandii (Fernald) Raymond
- Scirpus Pumilus Vahl var. rollandii (Fernald) Beetle
- Scirpus Pungens Vahl
- Scirpus Pungens Vahl ssp. monophyllus (J. Presl & C. Presl) Roy L. Taylor & MacB
- Scirpus Pungens Vahl var. longisetus Benth. & F. Muell.
- Scirpus Pungens Vahl var. longispicatus (Britton) Roy L. Taylor & MacBryde
- Scirpus Pungens Vahl var. polyphyllus Boeckeler
- Scirpus Purshianus Fernald
- Scirpus Quadrangulatus Michx.
- Scirpus Quadrangulatus Muhl., non Michx.
- Scirpus Quinquangularis Vahl
- Scirpus Quinqueflorus Hartmann
- Scirpus Raynalii Schuyler
- Scirpus Rehmanii Ridley
- Scirpus Retroflexus Poir.
- Scirpus Retrofractus L.
- Scirpus Robustus Pursh
- Scirpus Robustus Pursh var. novae-angliae (Britton) Beetle
- Scirpus Rockii Kük.
- Scirpus Rollandii Fernald
- Scirpus Rostellatus Torr.
- Scirpus Rubiginosus Beetle p.p.
- Scirpus Rubricosus Fernald
- Scirpus Rubrotinctus Fernald
- Scirpus Rufus (Huds.) Schrad.
- Scirpus Rufus (Huds.) Schrad. var. neogaeus Fernald
- Scirpus Saximontanus Fernald
- Scirpus Schaffneri Boeckeler
- Scirpus Scheuchzeri Bruegger 1882, non Vitman
- Scirpus Schoenoides Retz.
- Scirpus Scirpoideus (Michx.) T. Koyama
- Scirpus Setaceus L.
- Scirpus Smithii A. Gray
- Scirpus Smithii A. Gray var. levisetus Fassett
- Scirpus Smithii A. Gray var. setosus Fernald
- Scirpus Smithii A. Gray var. williamsii (Fernald) T. Beetle
- Scirpus Spadiceus auct. non L.
- Scirpus Steinmetzii Fernald
- Scirpus Stenophyllus Elliott
- Scirpus Subterminalis Torr.
- Scirpus Subterminalis Torr. var. cylindricus (Torr.) T. Koyama
- Scirpus Supinus L. var. hallii (A. Gray) A. Gray
- Scirpus Supinus L. var. saximontanus (Fernald) T. Koyama
- Scirpus Supinus auct. non L.
- Scirpus Sylvaticus L. p.p.
- Scirpus Tabernaemontani C.C. Gmel.
- Scirpus Tenuiculmis (Sheldon) Soják
- Scirpus Torreyi Olney
- Scirpus Tortilis Link
- Scirpus Triqueter L.
- Scirpus Tuberculosa Michx.
- Scirpus Tuberosus auct. non Desf.
- Scirpus Uniglumis Link
- Scirpus Uninodis (Delile) Boiss. var. hallii (A. Gray) Beetle
- Scirpus Vahlii Lam.
- Scirpus Validus Vahl
- Scirpus Validus Vahl var. creber Fernald
- Scirpus Verecundus Fernald
- Scirpus Wilkensii Schuyler
- Scirpus Wolfii A. Gray
- Scirpus ×contortus (Eames) T. Koyama
- Scirpus ×kuekenthalianus Junge 1905
- Scirpus ×oblongus T. Koyama
- Scleranthus Annuus L. ssp. annuus
- Scleria Brittonii Core ex Small
- Scleria Canescens Boeckeler
- Scleria Ciliata Michx. var. curtissii (Britton) Kessler
- Scleria Ciliata Michx. var. elliottii (Chapm.) Fernald
- Scleria Costata (Britton) Small
- Scleria Curtissii Britton
- Scleria Distans Poir.
- Scleria Doradoensis Britton
- Scleria Elliottii Chapm.
- Scleria Flaccida Steud.
- Scleria Gracilis Elliott, non Rich.
- Scleria Grisebachii C.B. Clarke
- Scleria Interrupta Rich.
- Scleria Laevis Willd., orth. var.
- Scleria Melaleuca Rchb. ex Schltdl. & Cham.
- Scleria Mitis P.J. Bergius [excluded]
- Scleria Mucronata Poir.
- Scleria Nitida Muhl. ex Willd.
- Scleria Nutans Willd. ex Kunth
- Scleria Pauciflora Muhl. ex Willd. var. glabra Chapm.
- Scleria Pauciflora Muhl. ex Willd. var. kansana Fernald
- Scleria Purpurascens Steud.
- Scleria Reticularis Michx. var. pubescens Britton
- Scleria Reticularis Michx. var. pumila Britton
- Scleria Setacea auct. non Poir.
- Scleria Stevensiana Britton
- Scleria Tenella Kunth
- Sclerocactus Blainei S.L. Welsh & Thorne
- Sclerocactus Brevihamatus (Engelm.) D.R. Hunt
- Sclerocactus Brevihamatus (Engelm.) D.R. Hunt ssp. brevihamatus
- Sclerocactus Brevihamatus (Engelm.) D.R. Hunt ssp. tobuschii (W.T. Marshall) N.P. Taylor
- Sclerocactus Cloveriae K.D. Heil & J.M. Porter
- Sclerocactus Cloveriae K.D. Heil & J.M. Porter ssp. brackii K.D. Heil & J.M. Porter
- Sclerocactus Contortus K.D. Heil
- Sclerocactus Erectocentrus (J.M. Coult.) N.P. Taylor
- Sclerocactus Havasupaiensis Clover
- Sclerocactus Intermedius Peebles
- Sclerocactus Intertextus (Engelm.) N.P. Taylor
- Sclerocactus Intertextus (Engelm.) N.P. Taylor var. dasyacanthus (Engelm.) N.P. Taylor
- Sclerocactus Intertextus (Engelm.) N.P. Taylor var. intertextus
- Sclerocactus Johnsonii (Parry ex Engelm.) N.P. Taylor
- Sclerocactus Mariposensis (Hester) N.P. Taylor
- Sclerocactus Parviflorus Clover & Jotter var. blessingiae W.H. Earle
- Sclerocactus Parviflorus Clover & Jotter var. intermedius (Peebles) Woodruff & L.D. Benso
- Sclerocactus Pubispinus (Engelm.) L.D. Benson var. sileri L.D. Benson
- Sclerocactus Pubispinus (Engelm.) L.D. Benson var. spinosior (Engelm.) S.L. Welsh
- Sclerocactus Scheeri (Salm-Dyck) N.P. Taylor
- Sclerocactus Schlesseri K.D. Heil & S.L. Welsh
- Sclerocactus Terrae-canyonae K.D. Heil
- Sclerocactus Uncinatus (Galeotti) N.P. Taylor
- Sclerocactus Uncinatus (Galeotti) N.P. Taylor ssp. wrightii (Engelm.) N.P. Taylor
- Sclerocactus Uncinatus (Galeotti) N.P. Taylor var. uncinatus (Galeotti) N.P. Taylor [ex
- Sclerocactus Uncinatus (Galeotti) N.P. Taylor var. wrightii (Engelm.) N.P. Taylor
- Sclerocactus Warnockii (L.D. Benson) N.P. Taylor
- Sclerocactus Wetlandicus Hochstätter var. ilseae Hochstätter
- Sclerocactus Whipplei (Engelm. & J. M. Bigelow) Britton & Rose var. glaucus (J.A. Purp
- Sclerocactus Whipplei (Engelm. & J. M. Bigelow) Britton & Rose var. ilseae (Hochstätte
- Sclerocactus Whipplei (Engelm. & J.M. Bigelow) Britton & Rose var. heilii Castetter, P
- Sclerocactus Whipplei (Engelm. & J.M. Bigelow) Britton & Rose var. intermedius (Peeble
- Sclerocactus Whipplei (Engelm. & J.M. Bigelow) Britton & Rose var. reevesii Castetter,
- Sclerocactus Whipplei (Engelm. & J.M. Bigelow) Britton & Rose var. roseus (Clover) L.D
- Sclerocactus Whipplei (Engelm. & J.M. Bigelow) Britton & Rose var. spinosior (Engelm.)
- Sclerocarya - Sclerocarya Caffra Sonder
- Sclerocarya - Sclerocarya Hochst.
- Sclerolinon - Sclerolinon C.m. Rogers
- Sclerophora Amabilis (Tibell) Tibell
- Sclerophora Coniophaea (Norman) J. Mattsson & Middelb.
- Sclerophora Lichen - Sclerophora Chevall.
- Sclerophora Lichen - Sclerophora Farinacea (Chevall.) Chevall.
- Sclerophora Lichen - Sclerophora Nivea (Hoffm.) Tibell
- Sclerophora Peronella (Ach.) Tibell
- Sclerophyton Lichen - Sclerophyton Eschw.
- Sclerophyton Lichen - Sclerophyton Inscriptum (Nyl.) Müll. Arg.
- Scleropoa Rigida (L.) Griseb.
- Scleropodium Apocladum (Mitt.) Grout
- Scleropodium Apocladum (Mitt.) Grout var. obtusum Grout
- Scleropodium Caespitosum Schimp.
- Scleropodium Caespitosum Schimp. var. sublaeve Renauld & Cardot
- Scleropodium Cespitans (Müll. Hal.) L.F. Koch var. laeve Renauld & Cardot
- Scleropodium Colpophyllum (Sull.) Grout
- Scleropodium Colpophyllum (Sull.) Grout var. attenuatum Grout
- Scleropodium Illecebrum Schimp.
- Scleropodium Moss - Scleropodium Julaceum E. Lawton
- Scleropodium Moss - Scleropodium Schimp.
- Scleropogon Longisetus Beetle
- Sclerostachya A. Camus
- Sclerostachya Fusca (Roxb.) A. Camus [excluded]
- Scoliciosporum Lichen - Scoliciosporum A. Massal.
- Scoliciosporum Lichen - Scoliciosporum Chlorococcum (Stenh.) Vezda
- Scoliciosporum Lichen - Scoliciosporum Umbrinum (Ach.) Arnold
- Scoliciosporum Sarothamni (Vain.) Vezda
- Scolosanthus Densiflorus auct. non Urb.
- Scolosanthus Multiflorus auct. non (Sw.) Krug & Urb.
- Scolosanthus - Scolosanthus Vahl
- Scolymus Grandiflorus Desf.
- Scopelophila Latifolia (Kindb.) Renauld & Cardot
- Scopelophila Moss - Scopelophila (mitt.) Lindb.
- Scopolia - Scopolia Jacq.
- Scorpidium Cossonii (Schimp.) Hedenäs
- Scorpidium Latifolium (Lindb. & Arnell) Paul
- Scorpidium Moss - Scorpidium (schimp.) Limpr.
- Scorpidium Moss - Scorpidium Scorpioides (Hedw.) Limpr.
- Scorpidium Revolvens (Sw.) Hedenäs
- Scorpidium Trifarium (F. Weber & D. Mohr) Paul
- Scorpidium Turgescens (T. Jensen) Loeske
- Scorpidium Vernicosum (Mitt.) Tuom.
- Scorpion Milkvetch - Astragalus Lentiginosus Douglas ex Hook. var. scorpionis M.E. Jones
- Scorpion Senna - Coronilla Emerus L.
- Scorpion Ticktrefoil - Desmodium Scorpiurus (Sw.) Desv.
- Scorpion's-tail - Heliotropium Angiospermum Murray
- Scorpion's-tail - Scorpiurus L.
- Scorpionbush - Carmona Cav.
- Scorpionbush - Carmona Retusa (Vahl) Masamune
- Scorpiurus Subvillosus L.
- Scorpiurus Sulcatus L.
- Scorpiurus Vermiculatus L.
- Scorzonella Laciniata (Hook.) Sch. Bip.
- Scorzonella Laciniata (Hook.) Sch. Bip. var. bolanderi (A. Gray) Jeps.
- Scorzonella Laciniata (Hook.) Sch. Bip. var. pratensis (Greene) Jeps.
- Scorzonella Leachiana M. Peck
- Scorzonella Leptosepala Nutt.
- Scorzonella Nutans Hook.
- Scorzonella Nutans Hook. var. major (A. Gray) M. Peck
- Scorzonella Procera Greene
- Scorzonella Troximoides (A. Gray) Jeps.
- Scorzonera - Scorzonera L.
- Scorzoneroides Autumnalis (L.) Moench
- Scotch Attorney - Clusia Rosea Jacq.
- Scotch Broom - Cytisus Scoparius (L.) Link
- Scotch Broom - Cytisus Scoparius (L.) Link var. andreanus (Puiss.) Dippel
- Scotch Broom - Cytisus Scoparius (L.) Link var. scoparius
- Scotch Cottonthistle - Onopordum Acanthium L.
- Scotch False Asphodel - Tofieldia Pusilla (Michx.) Pers.
- Scotch Heath - Erica Cinerea L.
- Scotch Laburnum - Laburnum Alpinum (Mill.) J. Presl
- Scotch Mist - Galium Sylvaticum L.
- Scotch Rose - Rosa Spinosissima L.
- Scotland Orache - Atriplex Glabriuscula Edmondston
- Scots Pine - Pinus Sylvestris L.
- Scott Mountain Bedstraw - Galium Serpenticum Dempster ssp. scotticum Dempster & Ehrend.
- Scott Mountain Phacelia - Howellanthus Dalesianus (J.T. Howell) Walden & R.Patt.
- Scott Valley Phacelia - Phacelia Greenei J.T. Howell
- Scott's Clematis - Clematis Hirsutissima Pursh var. scottii (Porter) Erickson
- Scotter's Fleabane - Erigeron Scotteri B. Boivin
- Scotter's Tortula Moss - Tortula Scotteri R.H. Zander & Steere
- Scotter's Whitlowgrass - Draba Scotteri G.A. Mulligan
- Scottish Licorice-root - Ligusticum Scoticum L.
- Scottish Licorice-root - Ligusticum Scoticum L. ssp. scoticum
- Scouler's Fumewort - Corydalis Scouleri Hook.
- Scouler's Popcornflower - Plagiobothrys Scouleri (Hook. & Arn.) I.M. Johnst.
- Scouler's Popcornflower - Plagiobothrys Scouleri (Hook. & Arn.) I.M. Johnst. var. scouleri
- Scouler's St. Johnswort - Hypericum Scouleri Hook.
- Scouler's St. Johnswort - Hypericum Scouleri Hook. ssp. scouleri
- Scouler's Surfgrass - Phyllospadix Scouleri Hook.
- Scouler's Valerian - Valeriana Scouleri Rydb.
- Scouler's Willow - Salix Scouleriana Barratt ex Hook.
- Scouler's Woollyweed - Hieracium Scouleri Hook.
- Scouler's Woollyweed - Hieracium Scouleri Hook. var. albertinum (Farr) G.W. Douglas & G.A. Allen
- Scouler's Woollyweed - Hieracium Scouleri Hook. var. nudicaule (A. Gray) Cronquist
- Scouler's Woollyweed - Hieracium Scouleri Hook. var. scouleri
- Scouringrush Horsetail - Equisetum Hyemale L.
- Scouringrush Horsetail - Equisetum Hyemale L. var. affine (Engelm.) A.A. Eaton
- Scrabrous Black Sedge - Carex Atratiformis Britton
- Scrambled Eggs - Corydalis Aurea Willd.
- Scrambling Fern - Diplopterygium Pinnatum (Kunze) Nakai
- Scrambling Nightshade - Solanum Tampicense Dunal
- Scranton Hawthorn - Crataegus Putata Sarg.
- Scratchbush - Urera Baccifera (L.) Gaudich.
- Scratchdaisy - Croptilon Raf.
- Scratchgrass - Muhlenbergia Asperifolia (Nees & Meyen ex Trin.) Parodi
- Scratchthroat - Parathesis Crenulata (Vent.) Hook. f.
- Screw-pod Wattle - Acacia Implexa Benth.
- Screwbean Mesquite - Prosopis Pubescens Benth.
- Screwleaf Muhly - Muhlenbergia Straminea Hitchc.
- Screwpine - Pandanus L. f.
- Screwstem - Bartonia Muhl. ex Willd.
- Screwtree - Helicteres Jamaicensis Jacq.
- Scribble Lichen - Opegrapha Ach.
- Scribble Lichen - Opegrapha Agelaea Fée
- Scribble Lichen - Opegrapha Astraea Tuck.
- Scribble Lichen - Opegrapha Atra Pers.
- Scribble Lichen - Opegrapha Candida Müll. Arg.
- Scribble Lichen - Opegrapha Filicina Mont.
- Scribble Lichen - Opegrapha Herbarum Mont.
- Scribble Lichen - Opegrapha Leucoplaca Müll. Arg.
- Scribble Lichen - Opegrapha Lithryga Ach.
- Scribble Lichen - Opegrapha Longissima Müll. Arg.
- Scribble Lichen - Opegrapha Microcycla Tuck.
- Scribble Lichen - Opegrapha Niveoatra (Borrer) J.R. Laundon
- Scribble Lichen - Opegrapha Ochrocheila Nyl.
- Scribble Lichen - Opegrapha Prosodea Ach.
- Scribble Lichen - Opegrapha Protuberans Zahlbr.
- Scribble Lichen - Opegrapha Rufescens Pers.
- Scribble Lichen - Opegrapha Rupestris Pers.
- Scribble Lichen - Opegrapha Varia Pers.
- Scribble Lichen - Opegrapha Viridis (Pers. ex Ach.) Behlen & Desberger
- Scribble Lichen - Opegrapha Vulgata Ach.
- Scribbly Gum - Eucalyptus Haemastoma Sm.
- Scribbly Gum - Eucalyptus Rossii R.T. Baker & H.G. Sm.
- Scribe Popcornflower - Plagiobothrys Scriptus (Greene) I.M. Johnst.
- Scribner Needlegrass - Achnatherum Scribneri (Vasey) Barkworth
- Scribner's Grass - Scribneria Bolanderi (Thurb.) Hack.
- Scribner's Grass - Scribneria Hack.
- Scribner's Hawkweed - Hieracium Scribneri Small
- Scribner's Ragwort - Senecio Integerrimus Nutt. var. scribneri (Rydb.) T.M. Barkley
- Scribner's Rosette Grass - Dichanthelium Oligosanthes (Schult.) Gould var. scribnerianum (Nash) Gould
- Script Lichen - Graphis Adans.
- Script Lichen - Graphis Aperiens Müll. Arg.
- Script Lichen - Graphis Botryosa Tuck.
- Script Lichen - Graphis Caesiella Vain.
- Script Lichen - Graphis Desquamescens (Fée) Zahlbr.
- Script Lichen - Graphis Dumastioides Fink
- Script Lichen - Graphis Glaucescens Fée
- Script Lichen - Graphis Insidiosa (C. Knight & Mitt.) Hook. f.
- Script Lichen - Graphis Intricata Fée
- Script Lichen - Graphis Leucopepla Tuck.
- Script Lichen - Graphis Lineola Ach.
- Script Lichen - Graphis Pavoniana Fée
- Script Lichen - Graphis Platycarpella Müll. Arg.
- Script Lichen - Graphis Poitaeoides Nyl.
- Script Lichen - Graphis Rimulosa (Mont.) Trevis.
- Script Lichen - Graphis Rufula (Trevis.) Mont.
- Script Lichen - Graphis Striatula (Ach.) Spreng.
- Script Lichen - Graphis Subamylacea Zahlbr.
- Script Lichen - Graphis Subnitidula Nyl.
- Script Lichen - Graphis Subparilis Nyl.
- Script Lichen - Graphis Tenella Ach.
- Script Lichen - Graphis Turbulenta Nyl.
- Scrobic - Paspalum Scrobiculatum L. var. bispicatum Hack.
- Scrophularia Aquatica L., nom. utique rej.
- Scrophularia Californica Cham. & Schltdl. var. desertorum Munz
- Scrophularia Californica Cham. & Schltdl. var. floribunda Greene
- Scrophularia Californica Cham. & Schltdl. var. laciniata Jeps.
- Scrophularia Californica Cham. & Schltdl. var. oregana (Pennell) B. Boivin
- Scrophularia Coccinea A. Gray
- Scrophularia Davidsonii Pennell
- Scrophularia Floribunda (Greene) A. Heller
- Scrophularia Glabrata Davidson
- Scrophularia Hoppii Koch
- Scrophularia Leporella E.P. Bicknell
- Scrophularia Multiflora Pennell
- Scrophularia Neomexicana R.J. Shaw
- Scrophularia Nodosa L. var. californica (Cham. & Schltdl.) M.E. Jones
- Scrophularia Occidentalis (Rydb.) E.P. Bicknell
- Scrophularia Pectinata Raf.
- Scrub Balm - Dicerandra Frutescens Shinners
- Scrub Balm - Dicerandra Frutescens Shinners ssp. frutescens
- Scrub Balm - Dicerandra Frutescens Shinners ssp. modesta R.B. Huck
- Scrub Gilia - Gilia Malior Day & V.E. Grant
- Scrub Hickory - Carya Floridana Sarg.
- Scrub Oak - Quercus Berberidifolia Liebm.
- Scrub Palmetto - Sabal Etonia Swingle ex Nash
- Scrub Plum - Prunus Geniculata Harper
- Scrub She-oak - Allocasuarina Paludosa (Sieber ex Spreng.) L.A.S. Johnson
- Scrub Spurge - Euphorbia Rosescens E.L.Bridges & Orzell
- Scrubland Goldenaster - Chrysopsis Subulata Small
- Sculptured Popcornflower - Plagiobothrys Glyptocarpus (Piper) I.M. Johnst.
- Sculptured Popcornflower - Plagiobothrys Glyptocarpus (Piper) I.M. Johnst. var. glyptocarpus
- Sculptured Popcornflower - Plagiobothrys Glyptocarpus (Piper) I.M. Johnst. var. modestus I.M. Johnst.
- Scurf Hoarypea - Tephrosia Chrysophylla Pursh
- Scurfpea - Cullen Medik.
- Scurfpea - Psoralidium Rydb.
- Scurfymallow - Malvella Lepidota (A. Gray) Fryxell
- Scurvygrass - Cochlearia L.
- Scutellaria Altamaha Small ssp. australis Epling
- Scutellaria Ambigua Nutt.
- Scutellaria Angustifolia Pursh var. canescens A. Gray
- Scutellaria Austiniae Eastw.
- Scutellaria Australis (Fassett) Epling
- Scutellaria Brevifolia A. Gray
- Scutellaria Cordifolia Muhl.
- Scutellaria Cuthbertii Alexander
- Scutellaria Epilobiifolia A. Ham.
- Scutellaria Galericulata L. ssp. pubescens (Benth.) Á. Löve & D. Löve
- Scutellaria Galericulata L. var. epilobiifolia (A. Ham.) Jordal
- Scutellaria Galericulata L. var. pubescens Benth.
- Scutellaria Helleri Small
- Scutellaria Holmgreniorum Cronquist
- Scutellaria Incana Biehler ssp. hispida (Benth.) Epling
- Scutellaria Integrifolia L. var. hispida Benth.
- Scutellaria Integrifolia L. var. multiglandulosa Kearney
- Scutellaria Leonardii Epling
- Scutellaria Mellichampii Small
- Scutellaria Minor auct. non Huds.
- Scutellaria Nana A. Gray var. sapphirina Barneby
- Scutellaria Nervosa Pursh var. ambigua (Nutt.) Fernald
- Scutellaria Nervosa Pursh var. calvifolia Fernald
- Scutellaria Ovalifolia Pers.
- Scutellaria Ovalifolia Pers. ssp. hirsuta (Short & Peter) Epling
- Scutellaria Ovalifolia Pers. ssp. mollis Epling
- Scutellaria Ovata Hill ssp. calcarea Epling
- Scutellaria Ovata Hill ssp. mississippiensis (Mart.) Epling
- Scutellaria Ovata Hill ssp. pseudovenosa Epling
- Scutellaria Ovata Hill ssp. versicolor (Nutt.) Epling
- Scutellaria Ovata Hill var. bracteata Benth.
- Scutellaria Ovata Hill var. calcarea (Epling) Gleason
- Scutellaria Ovata Hill var. pseudoarguta (Epling) Core
- Scutellaria Ovata Hill var. rugosa (Alph. Wood) Fernald
- Scutellaria Ovata Hill var. versicolor (Nutt.) Fernald
- Scutellaria Ovata Hill var. virginiana (Epling) Core
- Scutellaria Parvula Michx. var. leonardii (Epling) Fernald
- Scutellaria Pilosa Michx.
- Scutellaria Platyphylla (Epling) B.L. Turner & P. Delprete
- Scutellaria Potosina Brandegee ssp. parviflora Epling
- Scutellaria Potosina Brandegee var. grahmiana B.L. Turner, database artifact
- Scutellaria Punctata (Chapm.) Leonard
- Scutellaria Resinosa Torr. var. brevifolia (A. Gray) Penl.
- Scutellaria Saxatilis Riddell var. pilosior Benth.
- Scutellaria Serrata Andrews var. montana (Chapm.) Penl.
- Scutellaria Siphocamyploides Vatke, database artifact
- Scutellaria Tessellata Epling
- Scutellaria Tuberosa Benth. ssp. australis (Jeps.) Epling
- Scutellaria Tuberosa Benth. ssp. similis (Jeps.) Epling
- Scutellaria Tuberosa Benth. var. similis Jeps.
- Scutellaria Veronicifolia Rydb.
- Scutellaria Wrightii auct. non A. Gray
- Scutula Lichen - Scutula Stereocaulorum (Ach.) Körb.
- Scutula Lichen - Scutula Tul.
- Scutula Miliaris (Wallr.) Trevis.
- Scutula Tuberculosa (Th. Fr.) Rehm
- Scybalium - Scybalium Schott & Endl.
- Scyphiphora C.f. Gaertn.
- Scyphiphora Hydrophyllacea C.F. Gaertn., orth. var.
- Scyphiphora Hydrophyllacea Gaertn.
- Scytheleaf Onion - Allium Falcifolium Hook. & Arn.
- Sea Apple - Syzygium Grande (Wight) Wight ex Walp.
- Sea Aster - Tripolium Nees
- Sea Aster - Tripolium Pannonicum (Jacq.) Dobrocz.
- Sea Bilberry - Vaccinium Bracteatum Thunb.
- Sea Campion - Silene Uniflora Roth
- Sea Clover - Trifolium Squamosum L.
- Sea Dahlia - Coreopsis Maritima (Nutt.) Hook. f.
- Sea Daisy - Melanthera Biflora (L.) Wild
- Sea Fig - Carpobrotus Chilensis (Molina) N.E. Br.
- Sea Fig - Ficus Superba Miq.
- Sea Hibiscus - Hibiscus Tiliaceus L.
- Sea Kale - Crambe Maritima L.
- Sea Lavender - Limonium Mill.
- Sea Lettuce - Ulva Clathratioides L.G. Kraft, Kraft, & R.F. Waller
- Sea Lettuce - Ulva L.
- Sea Lettuce - Ulva Pertusa Kjellman
- Sea Milkwort - Glaux Maritima L.
- Sea Muilla - Muilla Maritima (Torr.) S. Watson
- Sea Putat - Barringtonia Asiatica (L.) Kurz
- Sea Rosemary - Argusia Boehmer
- Sea Rosemary - Argusia Gnaphalodes (L.) Heine
- Sea Rush - Juncus Maritimus Lam.
- Sea Sedge - Carex Marina Dewey
- Sea Sedge - Carex Marina Dewey ssp. marina
- Sea Spurge - Euphorbia Paralias L.
- Sea Torchwood - Amyris Elemifera L.
- Sea Wormwood - Artemisia Maritima L.
- Sea-daffodil - Pancratium Maritimum L.
- Sea-fern Grass - Catapodium Marinum (L.) C.E. Hubb.
- Sea-mango - Cerbera Manghas L.
- Sea-onion - Oncostema Verna (Huds.) Speta
- Seabeach Evening Primrose - Oenothera Humifusa Nutt.
- Seabean - Mucuna Gigantea (Willd.) DC.
- Seaberry - Haloragis J.r. Forst. & G. Forst.
- Seaberry - Hippophae L.
- Seaberry - Hippophae Rhamnoides L.
- Seablite - Suaeda Esteroa Ferren & Whitmore
- Seabluff Catchfly - Silene Douglasii Hook. var. oraria (M. Peck) C.L. Hitchc. & Maguire
- Seablush - Plectritis (lindl.) DC.
- Seacliff Beggarticks - Bidens Hillebrandiana (Drake) O. Deg.
- Seacliff Beggarticks - Bidens Hillebrandiana (Drake) O. Deg. ssp. hillebrandiana
- Seacliff Beggarticks - Bidens Hillebrandiana (Drake) O. Deg. ssp. polycephala Nagata & Ganders
- Seacliff Buckwheat - Eriogonum Parvifolium Sm.
- Seacliff Starviolet - Hedyotis Littoralis (Hillebr.) Fosberg
- Seacliff Tetramolopium - Tetramolopium Sylvae Lowrey
- Seacoast Angelica - Angelica Lucida L.
- Seacoast Marsh Elder - Iva Imbricata Walter
- Seagrape - Coccoloba Uvifera (L.) L.
- Seagrass - Halophila Minor (Zoll.) Hartog
- Seagrass - Halophila Ovalis (R. Br.) Hook. f.
- Seagrass - Halophila Ovata Gaudich.
- Seagrass - Halophila Thouars
- Seaheath - Frankenia L.
- Sealettuce - Dudleya Caespitosa (Haw.) Britton & Rose
- Seaoats - Uniola L.
- Seaoats - Uniola Paniculata L.
- Seaport Goosefoot - Chenopodium Opulifolium Schrad. ex W.D.J. Koch & Ziz
- Seapurslane - Sesuvium L.
- Searchlight Pricklypear - Opuntia ×curvospina Griffiths (pro sp.)
- Searls' Prairie Clover - Dalea Searlsiae (A. Gray) Barneby
- Searocket - Cakile Mill.
- Sears' Goatgrass - Aegilops Searsii M. Feldman & M. Kislev
- Searsia F.a. Barkley
- Searsia Lancea (L. f.) F.A. Barkley [excluded]
- Seashore Bentgrass - Agrostis Pallens Trin.
- Seashore Bluegrass - Poa Macrantha Vasey
- Seashore Cactus - Opuntia Martiniana (L.D. Benson) Parfitt
- Seashore Centipede Grass - Ischaemum Muticum L.
- Seashore Centipede Grass - Ischaemum Muticum L. var. aristuliferum Fosberg & Sachet
- Seashore Centipede Grass - Ischaemum Muticum L. var. muticum
- Seashore Dropseed - Sporobolus Virginicus (L.) Kunth
- Seashore False Bindweed - Calystegia Soldanella (L.) R. Br.
- Seashore Iris - Iris Spuria L.
- Seashore Iris - Iris Spuria L. ssp. ochroleuca (L.) Dykes
- Seashore Lupine - Lupinus Littoralis Douglas
- Seashore Paspalum - Paspalum Vaginatum Sw.
- Seashore Plantain - Plantago Macrocarpa Cham. & Schltdl.
- Seashore Saltbush - Atriplex Drymarioides Standl.
- Seashore Vervain - Verbena Litoralis Kunth
- Seasice Rush - Juncus Ambiguus Guss.
- Seaside Alder - Alnus Maritima (Marshall) Muhl. ex Nutt.
- Seaside Alkaligrass - Puccinellia Maritima (Huds.) Parl.
- Seaside Alumroot - Heuchera Pilosissima Fisch. & C.A. Mey.
- Seaside Alumroot - Heuchera Pilosissima Fisch. & C.A. Mey. var. hemisphaerica (Rydb.) Rosend.
- Seaside Alumroot - Heuchera Pilosissima Fisch. & C.A. Mey. var. pilosissima
- Seaside Amaranth - Amaranthus Pumilus Raf.
- Seaside Arrowgrass - Triglochin Maritima L.
- Seaside Barley - Hordeum Marinum Huds.
- Seaside Barley - Hordeum Marinum Huds. ssp. marinum
- Seaside Beebalm - Monarda Maritima (Cory) Correll
- Seaside Bird's Beak - Cordylanthus Rigidus (Benth.) Jeps. ssp. littoralis (Ferris) T.I. Chuang & Heckard
- Seaside Bird's-foot Trefoil - Lotus Formosissimus Greene
- Seaside Bittercress - Cardamine Angulata Hook.
- Seaside Brome - Bromus Maritimus (Piper) Hitchc.
- Seaside Brookweed - Samolus Valerandi L.
- Seaside Brookweed - Samolus Valerandi L. ssp. parviflorus (Raf.) Hultén
- Seaside Brookweed - Samolus Valerandi L. ssp. valerandi
- Seaside Buckwheat - Eriogonum Latifolium Sm.
- Seaside Buttonweed - Diodia Serrulata (P. Beauv.) G. Taylor
- Seaside Coccotrema Lichen - Coccotrema Maritimum Brodo
- Seaside Delosperma - Delosperma Litorale (Kensit) L. Bolus
- Seaside Disc Lichen - Buellia Maritima (A. Massal.) Bagl.
- Seaside Dock - Rumex Pallidus Bigelow
- Seaside Eryngo - Eryngium Maritimum L.
- Seaside Fleabane - Erigeron Glaucus Ker Gawl.
- Seaside Goldenrod - Solidago Sempervirens L.
- Seaside Goldenrod - Solidago Sempervirens L. var. mexicana (L.) Fernald
- Seaside Goldenrod - Solidago Sempervirens L. var. sempervirens
- Seaside Goldfields - Lasthenia Maritima (A. Gray) Ornduff
- Seaside Heliotrope - Heliotropium Curassavicum L. var. obovatum DC.
- Seaside Heliotrope - Heliotropium Curassavicum L. var. oculatum (A. Heller) I.M. Johnst.
- Seaside Joyweed - Alternanthera Maritima (Mart.) A. St.-Hil.
- Seaside Juniper - Juniperus Maritima R.P. Adams
- Seaside Kirschsteiniothelia Lichen - Kirschsteiniothelia Maritima (Linder) D. Hawksw.
- Seaside Knotweed - Polygonum Glaucum Nutt.
- Seaside Larkspur - Delphinium Parryi A. Gray ssp. maritimum (Davidson) Warnock
- Seaside Mahoe - Hibiscus Pernambucensis Arruda
- Seaside Nehe - Lipochaeta Succulenta (Hook. & Arn.) DC.
- Seaside Petunia - Calibrachoa Parviflora (Juss.) D'Arcy
- Seaside Primrose-willow - Ludwigia Maritima Harper
- Seaside Pussypaws - Cistanthe Maritima (Nutt.) Hershkovitz
- Seaside Ragwort - Senecio Pseudoarnica Less.
- Seaside Sandmat - Chamaesyce Polygonifolia (L.) Small
- Seaside Sandplant - Honckenya Peploides (L.) Ehrh.
- Seaside Sandplant - Honckenya Peploides (L.) Ehrh. ssp. diffusa (Hornem.) Hultén
- Seaside Sandplant - Honckenya Peploides (L.) Ehrh. ssp. major (Hook.) Hultén
- Seaside Sandplant - Honckenya Peploides (L.) Ehrh. ssp. peploides (L.) Ehrh. [excluded]
- Seaside Sandplant - Honckenya Peploides (L.) Ehrh. ssp. robusta (Fernald) Hultén
- Seaside Schistidium Moss - Schistidium Maritimum (Turner) Bruch & Schimp.
- Seaside Tansy - Borrichia Adans.
- Seaside Tansy - Borrichia ×cubana Britton & S.F. Blake (pro sp.)
- Seaside Threeawn - Aristida Tuberculosa Nutt.
- Seaside Tube Lichen - Hypogymnia Oceanica Goward
- Seaside Twintip - Stemodia Maritima L.
- Seaside Woolly Sunflower - Eriophyllum Stoechadifolium Lag.
- Seasonvine - Cissus Verticillata (L.) Nicolson & Jarvis
- Seaweed Lichen - Lichina C. Agardh
- Seaweed Lichen - Lichina Confinis (O.F. Müll.) C. Agardh
- Seawrack - Zostera Marina L.
- Sebastian-bush - Ditrysinia Raf.
- Sebastian-bush - Sebastiania Spreng.
- Sebastiania Corniculata (Vahl) Müll. Arg.
- Sebastiania Fruticosa (W. Bartram) Fernald
- Sebastiania Ligustrina (Michx.) Müll. Arg.
- Sebastopol Meadowfoam - Limnanthes Vinculans Ornduff
- Sebesten Rickseckeri (Millsp.) Britton
- Sebesten Sebestena (L.) Britton ex Small
- Sebucan - Leptocereus Grantianus Britton
- Secale Montanum Guss., nom. inq.
- Secale Orientale L.
- Secale Strictum (C. Presl) C. Presl
- Sechium - Sechium P. Br.
- Secoligia Geoica (Wahlenb. ex Ach.) Körb.
- Second Rockcress - Arabis Holboellii Hornem. var. retrofracta (Graham) Rydb.
- Secula Histrix (Poir.) Small p.p.
- Secula Viscidula (Michx.) Small
- Secund Jewelflower - Streptanthus Glandulosus Hook. ssp. secundus (Greene) Kruckeb.
- Secund Jewelflower - Streptanthus Glandulosus Hook. ssp. secundus (Greene) Kruckeb. var. hoffmanii Kruckeb.
- Secund Jewelflower - Streptanthus Glandulosus Hook. ssp. secundus (Greene) Kruckeb. var. secundus
- Secund Jewelflower - Streptanthus Glandulosus Hook. ssp. secundus (Greene) Kruckeb. var. sonomensis Kruckeb.
- Securidaca - Securidaca L.
- Securidaca Volubilis L.
- Securigera Orientalis (Mill.) Lassen
- Securigera Parviflora (Desv.) Lassen
- Securinega Acidoton (L.) Fawc. & Rendle
- Sedge - Abildgaardia Vahl
- Sedge - Carex Atrata L.
- Sedge - Carex Diluta M. Bieb.
- Sedge - Carex L.
- Sedge - Carex Sonomensis Stacey
- Sedge - Carex Timida Naczi & B.A. Ford
- Sedge - Carex Vacillans Drejer ex Hartm.
- Sedge - Carex ×abitibiana Lepage
- Sedge - Carex ×aestivaliformis Mack.
- Sedge - Carex ×arctophila F. Nyl.
- Sedge - Carex ×caesariensis Mack. (pro sp.)
- Sedge - Carex ×clausa Holmb.
- Sedge - Carex ×crinitoides Lepage
- Sedge - Carex ×deamii F.J. Herm.
- Sedge - Carex ×dumanii Lepage
- Sedge - Carex ×exsalina Lepage
- Sedge - Carex ×firmior (Norman) Holmb.
- Sedge - Carex ×flavicans F. Nyl.
- Sedge - Carex ×fulva Goodenough
- Sedge - Carex ×haematolepis Drejer (pro sp.)
- Sedge - Carex ×hartii Dewey (pro sp.)
- Sedge - Carex ×helvola Blytt (pro sp.)
- Sedge - Carex ×kenaica Lepage
- Sedge - Carex ×knieskernii Dewey (pro sp.)
- Sedge - Carex ×kyyhkynenii Hidén (pro sp.)
- Sedge - Carex ×limosoides J. Cay.
- Sedge - Carex ×limula Th. Fr. (pro sp.)
- Sedge - Carex ×massonii Cay. & Lepage
- Sedge - Carex ×mendica Lepage
- Sedge - Carex ×mirata Dewey (pro sp.)
- Sedge - Carex ×neobigelowii Lepage
- Sedge - Carex ×neofilipendula Lepage
- Sedge - Carex ×neomiliaris Lepage
- Sedge - Carex ×neorigida Lepage
- Sedge - Carex ×olneyi Boott
- Sedge - Carex ×oneillii Lepage
- Sedge - Carex ×paludivagans Drury (pro sp.)
- Sedge - Carex ×patuensis Lepage
- Sedge - Carex ×persalina Lepage
- Sedge - Carex ×physocarpoides Lepage
- Sedge - Carex ×pieperiana P. Junge
- Sedge - Carex ×pseudohelvola Kihlm. (pro sp.)
- Sedge - Carex ×quirponensis Fernald
- Sedge - Carex ×reducta S. Drejer (pro sp.)
- Sedge - Carex ×sardloqensis E. Dahl. (pro sp.)
- Sedge - Carex ×schatzii Kneucker
- Sedge - Carex ×spiculosa Fr. (pro sp.)
- Sedge - Carex ×stenolepis Less.
- Sedge - Carex ×subimpressa Clokey (pro sp.)
- Sedge - Carex ×subpaleacea J. Cay.
- Sedge - Carex ×subrecta J. Cay.
- Sedge - Carex ×subreducta Lepage
- Sedge - Carex ×subsalina Lepage
- Sedge - Carex ×subviridula Fernald
- Sedge - Carex ×sullivantii Boott
- Sedge - Carex ×trichina Fernald
- Sedge - Carex ×xanthocarpa Degland ex Loiseleur
- Sedge - Carex ×zahnii Kneucker
- Sedgeleaf Buckbrush - Ceanothus Cuneatus (Hook.) Nutt. var. fascicularis (McMinn) Hoover
- Seductive Entodon Moss - Entodon Seductrix (Hedw.) Müll. Hal.
- Sedum Aizoon L.
- Sedum Alaskanum (Rose) Rose ex Hutch.
- Sedum Alboroseum Baker
- Sedum Anopetalum DC.
- Sedum Cauticola Praeger
- Sedum Ciliosum Howell
- Sedum Cymosum (Nutt.) Fröd.
- Sedum Diffusum S. Watson
- Sedum Divericatum S. Watson
- Sedum Douglasii Hook.
- Sedum Douglasii Hook. ssp. ciliosum (Howell) R.T. Clausen
- Sedum Douglasii Hook. ssp. radiatum (S. Watson) R.T. Clausen
- Sedum Ellacombianum Praeger
- Sedum Erythrostictum Miq.
- Sedum Fabaria W.D.J. Koch
- Sedum Forsterianum Sm.
- Sedum Glanduliferum (L.F. Hend.) M. Peck
- Sedum Griffithsii Rose
- Sedum Heckneri M. Peck
- Sedum Hybridum L.
- Sedum Integrifolium (Raf.) A. Nelson
- Sedum Integrifolium (Raf.) A. Nelson ssp. leedyi (Rosend. & J.W. Moore) R.T. Clausen
- Sedum Integrifolium (Raf.) A. Nelson ssp. neomexicanum (Britton) R.T. Clausen
- Sedum Integrifolium (Raf.) A. Nelson ssp. procerum R.T. Clausen
- Sedum Kamtschaticum Fisch. & C.A. Mey. ssp. ellacombianum (Praeger) R.T. Clausen
- Sedum Lanceolatum Torr. var. nesioticum (G.N. Jones) C.L. Hitchc.
- Sedum Lanceolatum Torr. var. rupicola (G.N. Jones) C.L. Hitchc.
- Sedum Laxum (Britton) A. Berger ssp. eastwoodiae (Britton) R.T. Clausen
- Sedum Laxum (Britton) A. Berger ssp. latifolium R.T. Clausen
- Sedum Laxum (Britton) A. Berger ssp. perplexum R.T. Clausen
- Sedum Laxum (Britton) A. Berger ssp. retusum (Rose) R.T. Clausen
- Sedum Leibergii Britton var. borschii R.T. Clausen
- Sedum Leibergii Britton var. typicum R.T. Clausen
- Sedum Obtusatum A. Gray ssp. paradisum Denton
- Sedum Parvum Hemley
- Sedum Parvum Hemley ssp. nanifolium (Fröd.) R.T. Clausen
- Sedum Purdyi Jeps.
- Sedum Purpureum (L.) Schult.
- Sedum Rhodanthum A. Gray
- Sedum Robertsianum Alexander
- Sedum Rosea (L.) Scop.
- Sedum Rosea (L.) Scop. ssp. integrifolium (Raf.) Hultén
- Sedum Rosea (L.) Scop. var. alaskanum (Rose) A. Berger
- Sedum Rosea (L.) Scop. var. frigidum (Rydb.) Hultén
- Sedum Rosea (L.) Scop. var. integrifolium (Raf.) A. Berger
- Sedum Rosea (L.) Scop. var. leedyi Rosend. & J.W. Moore
- Sedum Rosea (L.) Scop. var. roanense (Britton) A. Berger
- Sedum Roseum (L.) Scop. ssp. integrifolium (Raf.) Hultén, orth. var.
- Sedum Roseum (L.) Scop. var. alaskanum (Rose) A. Berger, orth. var.
- Sedum Roseum (L.) Scop. var. frigidum (Rydb.) Hultén, orth. var.
- Sedum Roseum (L.) Scop. var. integrifolium (Raf.) A. Berger, orth. var.
- Sedum Roseum (L.) Scop. var. leedyi Rosend. & J.W. Moore, orth. var.
- Sedum Roseum (L.) Scop. var. roanense (Britton) A. Berger, orth. var.
- Sedum Roseum (L.) Scop., orth. var.
- Sedum Rubrotinctum R.T. Clausen
- Sedum Rupestre L.
- Sedum Rupestre L. var. forsterianum (Sm.) hort.
- Sedum Selskianum Regel & Maack
- Sedum Sieboldii Sweet ex Hook.
- Sedum Smallii (Britton ex Small) H.E. Ahles
- Sedum Spathulifolium Hook. ssp. anomalum (Britton) R.T. Clausen & Uhl
- Sedum Spathulifolium Hook. var. majus Praeger
- Sedum Spathulifolium Hook. var. pruinosum (Britton) B. Boivin
- Sedum Spectabile Boreau
- Sedum Spurium M. Bieb.
- Sedum Spurium M. Bieb. var. coccineum hort.
- Sedum Stenopetalum Pursh ssp. ciliosum (Howell) R.T. Clausen
- Sedum Stenopetalum Pursh ssp. radiatum (S. Watson) R.T. Clausen
- Sedum Subalpinum Blank.
- Sedum Telephioides Michx.
- Sedum Telephium L.
- Sedum Telephium L. ssp. fabaria (W.D.J. Koch) Schinz & R. Keller
- Sedum Telephium L. ssp. purpureum (L.) Schinz & Keller
- Sedum Texanum J.G. Sm.
- Sedum Triphyllum (Haw.) Gray
- Sedum Vigilimontis Small
- Sedum Wootonii Britton
- Sedum Yosemitense Britton
- Seedbox - Ludwigia Alternifolia L.
- Seely's Catchfly - Silene Seelyi Morton & J.W. Thomp.
- Seeman's Sunbonnets - Leibnitzia Lyrata (D. Don) G.L. Nesom
- Seep Arnica - Arnica Lonchophylla Greene ssp. arnoglossa (Greene) Maguire
- Seep Monkeyflower - Mimulus Guttatus DC.
- Seep Muhly - Muhlenbergia Reverchonii Vasey & Scribn.
- Seepweed - Suaeda Forssk. ex J.F. Gmel.
- Segestria Fr.
- Segestria Leptalea (Durieu & Mont.) R.C. Harris
- Segestria Mammillosa Th. Fr.
- Segestria Octomera (Müll. Arg.) R.C. Harris
- Segestria Rubentior (Stirt.) R.C. Harris
- Sego Lily - Calochortus Nuttallii Torr. & A. Gray
- Sehima Forssk.
- Sehima Ischaemoides Forssk.
- Sehima Nervosa (Rottler) Stapf, orth. var.
- Seifriz's Chamaedorea - Chamaedorea Seifrizii Burret
- Selaginella Albonitens Spring
- Selaginella Apoda (L.) Spring var. ludoviciana (A. Braun) B.F. Hansen & Wunderlin
- Selaginella Apus Spring
- Selaginella Arenicola Underw. ssp. acanthonota (Underw.) R. Tryon
- Selaginella Arenicola Underw. var. riddellii (Van Eselt.) Waterf.
- Selaginella Armata Baker var. eatonii (Hieron. ex Small) B.F. Hansen & Wunderlin
- Selaginella Caulescens (Wall. ex Hook. & Grev.) Spring
- Selaginella Ciliaris sensu Brack., non Retz.
- Selaginella Engelmannii Hieron.
- Selaginella Engelmannii Hieron. var. scopulorum (Maxon) C.F. Reed
- Selaginella Engelmannii Hieron. var. standleyi (Maxon) C.F. Reed
- Selaginella Mutica D.C. Eaton ex Underw. var. texana Weath.
- Selaginella Parvula Hillebr.
- Selaginella Pilifera A. Braun var. pringlei (Baker) Morton
- Selaginella Plagiochila sensu Krug & Urb., non Baker
- Selaginella Portoricensis A. Braun
- Selaginella Pseudo-volkensii Hosok., orth. var.
- Selaginella Riddellii Van Eselt.
- Selaginella Scopulorum Maxon
- Selaginella Sheldonii Maxon
- Selaginella Sintenisii Hieron.
- Selaginella Standleyi Maxon
- Selaginella Stipitata Spring [excluded]
- Selaginella Stolonifera (Sw.) Spring
- Selaginella Underwoodii Hieron. var. dolichotricha Weath.
- Selaginella ×neomexicana Maxon (pro sp.)
- Selby's Rockcress - Arabis Selbyi Rydb.
- Selenia Aptera (S. Watson) Small
- Selenia - Selenia Nutt.
- Selenicereus Innesii M. Kimnach [excluded]
- Selenicereus Macdonaldiae (Hook.) Britton & Rose
- Selfheal - Prunella L.
- Selfing Monkeyflower - Mimulus Cleistogamus J.T. Howell
- Selfing Willowherb - Epilobium Cleistogamum (Curran) Hoch & P.H. Raven
- Seliger's Herzogiella Moss - Herzogiella Seligeri (Brid.) Z. Iwats.
- Seligeria Donnii Lindb.
- Selinocarpus Chenopodioides A. Gray
- Selinocarpus Diffusus A. Gray ssp. nevadensis Standl.
- Selinum Monnieri L.
- Selinum - Selinum L.
- Selkirk's Violet - Viola Selkirkii Pursh ex Goldie
- Selloa Glutinosa Spreng.
- Selway Mariposa Lily - Calochortus Elegans Pursh var. selwayensis (H. St. John) Ownbey
- Selwyn's Atrichum Moss - Atrichum Selwynii Austin
- Selwyn's Pylaisiella Moss - Pylaisiella Selwynii (Kindb.) H.A. Crum, Steere & L.E. Anderson
- Semaphore Pricklypear - Consolea Corallicola Small
- Semaphore Thoroughwort - Eupatorium Mikanioides Chapm.
- Semaphoregrass - Pleuropogon R. Br.
- Sematophyllum Caespitosum auct. Amer.
- Sematophyllum Carolinianum (Müll. Hal.) E. Britton
- Sematophyllum Carolinianum (Müll. Hal.) E. Britton var. admixtum (Sull.) Grout
- Sematophyllum Micans (Mitt.) Braithw.
- Sematophyllum Moss - Sematophyllum Adnatum (Michx.) E. Britton
- Sematophyllum Moss - Sematophyllum Demissum (Wilson) Mitt.
- Sematophyllum Moss - Sematophyllum Mitt.
- Sematophyllum Moss - Sematophyllum Subpinnatum (Brid.) E. Britton
- Sematophyllum Novae-caesareae (Austin) E. Britton
- Sematophyllum Smallii R.S. Williams
- Semecarpus - Semecarpus Cassuvium Roxb.
- Semecarpus - Semecarpus L. f.
- Semecarpus Venenosa Volkens, orth. var.
- Semiarundinaria Makino
- Seminole Balsamo - Psychotria Nervosa Sw.
- Seminole False Foxglove - Agalinis Filifolia (Nutt.) Raf.
- Sempervivum Heuffelii Schott
- Senator Mine Alumroot - Heuchera Eastwoodiae Rosend., Butters & Lakela
- Sendtner's Drepanocladus Moss - Drepanocladus Sendtneri (Schimp.) Warnst.
- Sendtner's Molendoa Moss - Molendoa Sendtneriana (Bruch & Schimp.) Limpr.
- Sendtner's Polyplastia Lichen - Polyblastia Sendtneri Krempelh.
- Seneca Snakeroot - Polygala Senega L.
- Senecio Actinella Greene var. mogollonicus (Greene) Greenm.
- Senecio Acutidens Rydb.
- Senecio Adamsii Howell
- Senecio Admirabilis Greene
- Senecio Alabamensis Britton ex Small
- Senecio Alaskanus Hultén
- Senecio Ambrosioides Rydb.
- Senecio Amplectens A. Gray var. taraxacoides A. Gray
- Senecio Anonymus Alph. Wood
- Senecio Antennariifolius Britton
- Senecio Anteuphorbium (L.) Sch. Bip.
- Senecio Argutus A. Rich.
- Senecio Atropurpureus (Ledeb.) Fedtsch.
- Senecio Atropurpureus (Ledeb.) Fedtsch. ssp. frigidus (Richardson) Hultén
- Senecio Atropurpureus (Ledeb.) Fedtsch. ssp. tomentosus (Kjellm.) Hultén
- Senecio Atropurpureus (Ledeb.) Fedtsch. var. dentatus (A. Gray) Hultén
- Senecio Atropurpureus (Ledeb.) Fedtsch. var. ulmeri (Steffen) A.E. Porsild
- Senecio Aureus L.
- Senecio Aureus L. var. aquilonius Fernald
- Senecio Aureus L. var. borealis Torr. & A. Gray
- Senecio Aureus L. var. gracilis (Pursh) Hook.
- Senecio Aureus L. var. intercursus Fernald
- Senecio Aureus L. var. semicordatus (Mack. & Bush) Greenm.
- Senecio Aureus L. var. werneriifolius A. Gray
- Senecio Balsamitae Muhl. ex Willd.
- Senecio Bernardinus Greene
- Senecio Bicolor (Willd.) Todaro ssp. cineraria (DC.) Chater
- Senecio Bicolor auct. non (Willd.) Todaro, nom. illeg.
- Senecio Bivestitus Cronquist
- Senecio Blitoides Greene
- Senecio Bolanderi A. Gray
- Senecio Bolanderi A. Gray var. harfordii (Greenm.) T.M. Barkley
- Senecio Breweri Burtt Davy
- Senecio Cacalioides Fisch. ex Spreng.
- Senecio Canus Hook.
- Senecio Capillaris Gaudich.
- Senecio Cardamine Greene
- Senecio Carlomasonii B.L. Turner & T.M. Barkley
- Senecio Carthamoides Greene
- Senecio Castoreus S.L. Welsh
- Senecio Cernuus A. Gray, non L. f.
- Senecio Clevelandii Greene
- Senecio Clevelandii Greene var. heterophyllus Hoover
- Senecio Cliffordii N.D. Atwood & S.L. Welsh
- Senecio Clivorum Maxim.
- Senecio Columbianus Greene
- Senecio Confusus Britten & Rendle
- Senecio Congestus (R. Br.) DC. ssp. tonsus (Fernald) Á. Löve & D. Löve
- Senecio Congestus (R. Br.) DC. var. palustris (L.) Fernald
- Senecio Congestus (R. Br.) DC. var. tonsus Fernald
- Senecio Conterminus Greenm.
- Senecio Convallium Greenm.
- Senecio Covillei Greene
- Senecio Covillei Greene var. scorzonella (Greene) Jeps.
- Senecio Crassulus A. Gray var. cusickii (Piper) Greenm.
- Senecio Crawfordii (Britton) G.W. Douglas & G. Ruyle-Douglas
- Senecio Crepidineus Greene
- Senecio Crocatus Rydb.
- Senecio Crocatus Rydb. var. wolfii Greenm.
- Senecio Cruentus DC.
- Senecio Cymbalaria Pursh
- Senecio Cymbalarioides H. Buek
- Senecio Cymbalarioides H. Buek ssp. moresbiensis Calder & Roy L. Taylor
- Senecio Cymbalarioides Nutt. var. borealis (Torr. & A. Gray) Greenm.
- Senecio Cymbalarioides Nutt. var. suksdorfii (Greenm.) M. Peck
- Senecio Cymbalarioides Nutt., non H. Buek, nom. illeg.
- Senecio Cynthioides Greene
- Senecio Debilis Nutt.
- Senecio Densus Greene
- Senecio Dimorphophyllus Greene
- Senecio Dimorphophyllus Greene var. intermedius T.M. Barkley
- Senecio Dimorphophyllus Greene var. paysonii T.M. Barkley
- Senecio Discoideus (Hook.) Britton
- Senecio Douglasii DC.
- Senecio Douglasii DC. ssp. longilobus (Benth.) W.A. Weber
- Senecio Douglasii DC. var. jamesii (Torr. & A. Gray) Ediger ex Correll & M.C. John
- Senecio Douglasii DC. var. longilobus (Benth.) L.D. Benson
- Senecio Douglasii DC. var. monoensis (Greene) Jeps.
- Senecio Douglasii DC. var. tularensis Munz
- Senecio Eremophilus Richardson ssp. kingii (Rydb.) G.W. Douglas & G. Ruyle-Douglas
- Senecio Eremophilus Richardson ssp. macdougalii (A. Heller) G.W. Douglas & G. Ruyle-
- Senecio Erraticus Bertol.
- Senecio Eurycephalus Torr. & A. Gray
- Senecio Eurycephalus Torr. & A. Gray var. lewisrosei (J.T. Howell) T.M. Barkley
- Senecio Eurypterus Greenm.
- Senecio Exaltatus Nutt.
- Senecio Fedifolius Rydb.
- Senecio Fendleri A. Gray
- Senecio Fendleri A. Gray var. lanatus Osterh.
- Senecio Filifolius Nutt., non P.J. Bergius
- Senecio Flavulus Greene
- Senecio Flettii Wiegand
- Senecio Flocciferus DC.
- Senecio Foetidus J.T. Howell
- Senecio Foetidus J.T. Howell var. hydrophiloides (Rydb.) T.M. Barkley ex Cronquis
- Senecio Franciscanus Greene
- Senecio Fremontii Torr. & A. Gray ssp. blitoides (Greene) W.A. Weber
- Senecio Fremontii Torr. & A. Gray ssp. occidentalis (A. Gray) G.W. Douglas & G. Ru
- Senecio Frigidus (Richardson) Less.
- Senecio Fulgens Rydb.
- Senecio Fuscatus auct. non Hayek
- Senecio Ganderi T.M. Barkley & R.M. Beauch.
- Senecio Gaspensis Greenm.
- Senecio Gaspensis Greenm. var. firmifolius (Greenm.) Fernald
- Senecio Gibbsonsii Greene
- Senecio Glabellus Poir.
- Senecio Glaucifolius Rydb.
- Senecio Glomeratus Desf. ex Poir.
- Senecio Gracilis Pursh
- Senecio Grandifolius Less.
- Senecio Greenei A. Gray
- Senecio Greggii Rydb.
- Senecio Hallii Britton
- Senecio Hallii Britton var. discoidea W.A. Weber
- Senecio Harbourii Rydb.
- Senecio Harfordii Greenm.
- Senecio Hartianus A. Heller
- Senecio Hartwegii Benth.
- Senecio Hesperius Greene
- Senecio Heterodoxus Greene ex Rydb.
- Senecio Hieraciifolius L.
- Senecio Holmii Greene
- Senecio Hookeri Torr. & A. Gray
- Senecio Howellii Greene
- Senecio Huachucanus A. Gray
- Senecio Hybridus (Willd.) Regel
- Senecio Hyperborealis Greenm.
- Senecio Imparipinnatus Klatt
- Senecio Indecorus Greene
- Senecio Integerrimus Nutt. var. lugens (Richardson) B. Boivin
- Senecio Integerrimus Nutt. var. vaseyi (Greenm.) Cronquist
- Senecio Integrifolius (L.) Clairv.
- Senecio Ionophyllus Greene
- Senecio Ionophyllus Greene var. sparsilobatus (Parish) H.M. Hall
- Senecio Jonesii Rydb.
- Senecio Kingii Rydb.
- Senecio Kjellmanii A.E. Porsild
- Senecio Laetiflorus Greene
- Senecio Layneae Greene
- Senecio Leonardii Rydb.
- Senecio Lewisrosei J.T. Howell
- Senecio Ligulifolius Greene
- Senecio Lindstroemii (Ostenf.) A.E. Porsild
- Senecio Lobatus Pers.
- Senecio Longilobus Benth.
- Senecio Longipetiolatus Rydb.
- Senecio Lugens Richardson var. exaltatus (Nutt.) A. Gray
- Senecio Lugens Richardson var. ochroleucus A. Gray
- Senecio Lynceus Greene
- Senecio Lynceus Greene var. leucoreus (Greenm.) S.F. Blake
- Senecio Macdougalii A. Heller
- Senecio Macounii Greene
- Senecio Malmstenii S.F. Blake ex Tidestr.
- Senecio Manitobensis Greenm.
- Senecio Memmingeri Britton
- Senecio Metcalfei Greene
- Senecio Mikanioides Otto ex Walp.
- Senecio Millefolium Torr. & A. Gray
- Senecio Millelobatus Rydb.
- Senecio Minimus Poir.
- Senecio Molinarius Greenm.
- Senecio Monoensis Greene
- Senecio Moresbiensis (Calder & Roy L. Taylor) G.W. Douglas & G. Ruyle-Douglas
- Senecio Muehlenbergii Sch. Bip.
- Senecio Muirii Greenm.
- Senecio Multicapitatus Greenm. ex Rydb.
- Senecio Multilobatus Torr. & A. Gray ex A. Gray
- Senecio Murrayi Bornm.
- Senecio Mutabilis Greene
- Senecio Neomexicanus A. Gray
- Senecio Neomexicanus A. Gray var. griffithsii Greenm.
- Senecio Neomexicanus A. Gray var. metcalfei (Greene) T.M. Barkley
- Senecio Neomexicanus A. Gray var. mutabilis (Greene) T.M. Barkley
- Senecio Neomexicanus A. Gray var. toumeyi (Greene) T.M. Barkley
- Senecio Newcombei Greene
- Senecio Obovatus Muhl. ex Willd.
- Senecio Obovatus Muhl. ex Willd. var. elliottii (Torr. & A. Gray) Fernald
- Senecio Obovatus Muhl. ex Willd. var. rotundus Britton
- Senecio Ogotorukensis Packer
- Senecio Oodes Rydb.
- Senecio Oresbius Greenm.
- Senecio Palmensis (Nees) C. Sm. ex Link
- Senecio Palustris (L.) Hook.
- Senecio Pammelii Greenm.
- Senecio Pauciflorus Pursh
- Senecio Pauciflorus Pursh var. fallax (Greenm.) Greenm.
- Senecio Pauciflorus Pursh var. jucundulus Jeps.
- Senecio Pauperculus Michx.
- Senecio Pauperculus Michx. var. balsamitae (Muhl. ex Willd.) Fernald
- Senecio Pauperculus Michx. var. crawfordii (Britton) T.M. Barkley
- Senecio Pauperculus Michx. var. firmifolius (Greenm.) Greenm.
- Senecio Pauperculus Michx. var. neoscoticus Fernald
- Senecio Pauperculus Michx. var. praelongus (Greenm.) House
- Senecio Pauperculus Michx. var. thompsoniensis (Greenm.) B. Boivin
- Senecio Pereziifolius Rydb.
- Senecio Petasitis (Sims) DC.
- Senecio Plattensis Nutt.
- Senecio Platylobus Rydb.
- Senecio Porteri Greene
- Senecio Pseudaureus Rydb.
- Senecio Pseudaureus Rydb. ssp. flavulus (Greene) G.W. Douglas & G. Ruyle-Douglas
- Senecio Pseudaureus Rydb. ssp. semicordatus (Mack. & Bush) G.W. Douglas & G. Ruyle-D
- Senecio Pseudaureus Rydb. var. flavulus (Greene) Greenm.
- Senecio Pseudaureus Rydb. var. semicordatus (Mack. & Bush) T.M. Barkley
- Senecio Pseudotomentosus Mack. & Bush
- Senecio Purshianus Nutt.
- Senecio Quaerens Greene
- Senecio Quercetorum Greene
- Senecio Resedifolius Less.
- Senecio Robbinsii Oakes ex Rusby
- Senecio Rotundus (Britton) Small
- Senecio Rubricaulis Greene
- Senecio Rugelia A. Gray
- Senecio Salignus DC.
- Senecio Sandvicensis auct. non Less.
- Senecio Sanguisorboides Rydb.
- Senecio Saxosus Klatt
- Senecio Saxosus Klatt var. toiyabensis Greenm.
- Senecio Schweinitzianus Nutt.
- Senecio Scribneri Rydb.
- Senecio Seemanii auct. non Sch. Bip. ex Seem.
- Senecio Semicordatus Mack. & Bush
- Senecio Serra Hook. var. altior Jeps.
- Senecio Serra Hook. var. integriusculus A. Gray
- Senecio Smallii Britton
- Senecio Spartioides Torr. & A. Gray var. fremontii (Torr. & A. Gray) Greenm.
- Senecio Spartioides Torr. & A. Gray var. granularis Maguire & A.H. Holmgren ex Cronq
- Senecio Spartioides Torr. & A. Gray var. parksii (Cory) Shinners
- Senecio Spellenbergii T.M. Barkley
- Senecio Streptanthifolius Greene
- Senecio Streptanthifolius Greene var. borealis (Torr. & A. Gray) J.F. Bain
- Senecio Streptanthifolius Greene var. kluanei J.F. Bain
- Senecio Streptanthifolius Greene var. laetiflorus (Greene) J.F. Bain
- Senecio Streptanthifolius Greene var. moresbiensis (Calder & Roy L. Taylor) B. Boivin
- Senecio Streptanthifolius Greene var. oodes (Rydb.) J.F. Bain
- Senecio Streptanthifolius Greene var. rubricaulis (Greene) J.F. Bain
- Senecio Streptanthifolius Greene var. wallowensis J.F. Bain
- Senecio Stygius Greene
- Senecio Suaveolens (L.) Elliott, nom. illeg.
- Senecio Subcuneatus Rydb.
- Senecio Subnudus DC.
- Senecio Suksdorfii Greenm.
- Senecio Tampicanus DC.
- Senecio Thornberi Greenm.
- Senecio Thurberi A. Gray
- Senecio Tichomirovii auct. non Schischkin
- Senecio Toiyabensis S.L. Welsh & Goodrich
- Senecio Tomentosus Michx.
- Senecio Toumeyi Greene
- Senecio Triangularis Hook. var. angustifolius G.N. Jones
- Senecio Tridenticulatus Rydb.
- Senecio Tundricola auct. non Tolm.
- Senecio Tweedyi Rydb.
- Senecio Uintahensis (A. Nelson) Greenm.
- Senecio Valerianifolius Link ex Spreng.
- Senecio Vaseyi Greenm.
- Senecio Wardii Greene
- Senecio Webbii (Sch. Bip.) Christ
- Senecio Websteri Greenm., non Hook. f.
- Senecio Werneriifolius (A. Gray) A. Gray
- Senecio Werneriifolius (A. Gray) A. Gray var. alpinus (A. Gray) Dorn
- Senecio Werneriifolius (A. Gray) A. Gray var. incertus Greenm.
- Senecio Wrightii Greenm.
- Senecio Yukonensis A.E. Porsild
- Senecioides Cinerea (L.) Kuntze ex Britton & P. Wilson
- Senegal Boscia - Boscia Senegalensis (Pers.) Lam. ex Poir.
- Senegal Date Palm - Phoenix Reclinata Jacq.
- Senegal Mahogany - Khaya Senegalensis (Desr.) A. Juss.
- Senegal Saba - Saba Senegalensis (A. DC.) Pichon
- Senegalia Erubescens (Welw. ex Oliv.) Kyal. & Boatwr.
- Senegalia Galpinii (Burtt Davy) Seigler & Ebinger
- Senegalia Goetzei (Harms) Kyal. & Boatwr.
- Senegalia Mellifera (Vahl) L.A.Silva & J.Freitas
- Senegalia Mellifera (Vahl) Seigler & Ebinger ssp. detinens (Burch.) Kyal. & Boatwr.
- Senegalia Mellifera (Vahl) Seigler & Ebinger, nom. inval.
- Senegalia Nigrescens (Oliv.) P.J.H. Hurter
- Senegalia Pennata (L.) Maslin
- Senegalia Polyacantha (Willd.) Seigler & Ebinger ssp. campylacantha (Hochst. ex A. Ric
- Senegalia Schweinfurthii (Brenan & Exell) Seigler & Ebinger
- Senegalia Senegal (L.) Britton var. rostrata (Brenan) Kyal. & Boatwr.
- Senegalia Skleroxyla (Tussac) Seigler & Ebinger [excluded]
- Senegalia Visco (Lorentz ex Griseb.) Seigler & Ebinger
- Senegalia ×turneri Seigler, Ebinger, & C.E. Glass, nom. inval.
- Senfft's Fig - Ficus Senfftiana Warb.
- Senita Cactus - Pachycereus Schottii (Engelm.) D.R. Hunt
- Senkenbergia Coulteri Hook. f.
- Senna Aciphylla (Benth.) Randell
- Senna Angulata (Vogel) H.S. Irwin & Barneby
- Senna Angustifolia (Vahl) Batka
- Senna Artemisioides (Gaudich. ex DC.) Randell ssp. circinnata (Benth.) Randell
- Senna Artemisioides (Gaudich. ex DC.) Randell ssp. petiolaris Randell
- Senna Artemisioides (Gaudich. ex DC.) Randell ssp. zygophylla (Benth.) Randell
- Senna Candolleana (Vogel) H.S. Irwin & Barneby
- Senna Coronilloides (Benth.) Randell
- Senna Fructicosa (Mill.) Irwin & Barneby [excluded]
- Senna Glutinosa (DC.) Randell
- Senna Glutinosa (DC.) Randell ssp. chatelainiana (Gaudich.) Randell
- Senna Hebecarpa (Fernald) Irwin & Barneby var. longipila (E.L. Braun) C.F. Reed
- Senna Hirsuta (L.) Irwin & Barneby var. leptocarpa (Benth.) H.S. Irwin & Barne
- Senna Macranthera (Collad.) H.S. Irwin & Barneby
- Senna Macranthera (Collad.) H.S. Irwin & Barneby var. micans (Nees) H.S. Irwin & B
- Senna Nemophila (A. Cunn. ex Vogel) ?, ined.
- Senna Notabilis (F. Muell.) Randell
- Senna Obovata (Collad.) Link
- Senna Odorata (R. Morris) Randell
- Senna Petersiana (Bolle) Lock
- Senna Pleurocarpa (F. Muell.) Randell
- Senna Pleurocarpa (F. Muell.) Randell var. pleurocarpa
- Senna Rostrata (Mart.) Irwin & Barneby [excluded]
- Senna - Senna Mill.
- Senna - Senna ×floribunda (Cav.) Irwin & Barneby
- Senna Septentrionalis (Viv.) Irwin & Barneby, database artifact
- Senna Spectabilis (DC.) Irwin & Barneby var. excelsa (Schrad.) H.S. Irwin & Barneb
- Senna Splendida (Vogel) H.S. Irwin & Barneby
- Senna Stipulacea (Aiton) H.S. Irwin & Barneby
- Sensitive Fern - Onoclea L.
- Sensitive Fern - Onoclea Sensibilis L.
- Sensitive Jointvetch - Aeschynomene Sensitiva Sw.
- Sensitive Jointvetch - Aeschynomene Sensitiva Sw. var. hispidula (Kunth) Rudd [excluded]
- Sensitive Jointvetch - Aeschynomene Sensitiva Sw. var. sensitiva
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. nictitans
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. nictitans var. aspera (Muhl. ex Elliott) Irwin
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. nictitans var. diffusa (DC.) Irwin & Barneby
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. nictitans var. jaliscensis (Greenm.) Irwin & Ba
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. nictitans var. leptadenia (Greenm.) Gandhi & Ha
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. nictitans var. nictitans
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. patellaria (DC. ex Collad.) Irwin & Barneby
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. patellaria (DC. ex Collad.) Irwin & Barneby var
- Sensitive Partridge Pea - Chamaecrista Nictitans (L.) Moench ssp. patellaria (DC. ex Collad.) Irwin & Barneby var
- Sensitive Pea - Chamaecrista (l.) Moench
- Sensitive Plant - Mimosa L.
- Sentry Milkvetch - Astragalus Cremnophylax Barneby
- Sentry Milkvetch - Astragalus Cremnophylax Barneby var. cremnophylax
- Sentry Milkvetch - Astragalus Cremnophylax Barneby var. hevronii Barneby
- Sentry Milkvetch - Astragalus Cremnophylax Barneby var. myriorrhaphis Barneby
- Sentrypalm - Howeia Forsteriana (C. Moore & F. Muell.) Becc.
- Separated Sedge - Carex Divisa Huds.
- Separateleaf Chickensage - Sphaeromeria Diversifolia (D.C. Eaton) Rydb.
- Sepi - Neurolaena Lobata (L.) Cass.
- September 11 Stickleaf - Mentzelia Memorabilis N.H. Holmgren & P.K. Holmgren
- September Elm - Ulmus Serotina Sarg.
- Septicweed - Senna Occidentalis (L.) Link
- Sequoia Bedstraw - Galium Sparsiflorum W. Wight
- Sequoia Bedstraw - Galium Sparsiflorum W. Wight ssp. glabrius Dempster & Stebbins
- Sequoia Bedstraw - Galium Sparsiflorum W. Wight ssp. sparsiflorum
- Sequoia False Goldenaster - Heterotheca Monarchensis York, Shevock & Semple
- Sequoia Gigantea (Lindl.) Decne.
- Sequoia Mycocalicium Lichen - Mycocalicium Sequoiae Bonar
- Sequoia Wellingtonia Seem.
- Serapias Atrorubens O. Hoffm.
- Serapias Helleborine L.
- Serbian Bellflower - Campanula Poscharskyana Degen
- Serbian Spruce - Picea Omorika (Pancic) Purk.
- Serendipity Berry - Dioscoreophyllum Cumminsii (Stapf) Diels
- Serenoa - Serenoa Hook. f.
- Serenoa Serrulata (Michx.) G. Nicholson
- Serianthes - Serianthes Benth.
- Sericea Lespedeza - Lespedeza Cuneata (Dum. Cours.) G. Don
- Sericocarpus Acutisquamosus (Nash) Small
- Sericocarpus Bifoliatus (Walter) Porter
- Sericocarpus Californicus Durand
- Sericocarpus Oregonensis Nutt. ssp. californicus (Durand) Ferris
- Sericocarpus Tomentellus Greene
- Sericotheca Discolor (Pursh) Rydb.
- Serillo Dulce - Schizachyrium Brevifolium (Sw.) Nees ex Büse
- Seringe Willow - Salix ×seringeana Gaudin
- Serinia Oppositifolia (Raf.) Kuntze
- Seriphidium Arbusculum (Nutt.) W.A. Weber
- Seriphidium Arbusculum (Nutt.) W.A. Weber ssp. longilobum (Osterh.) W.A. Weber
- Seriphidium Canum (Pursh) W.A. Weber
- Seriphidium Canum (Pursh) W.A. Weber ssp. bolanderi (A. Gray) W.A. Weber
- Seriphidium Canum (Pursh) W.A. Weber ssp. viscidulum (Osterh.) W.A. Weber
- Seriphidium Novum (A. Nelson) W.A. Weber
- Seriphidium Pygmaeum (A. Gray) W.A. Weber
- Seriphidium Rigidum (Nutt.) W.A. Weber
- Seriphidium Rothrockii (A. Gray) W.A. Weber
- Seriphidium Tridentatum (Nutt.) W.A. Weber
- Seriphidium Tridentatum (Nutt.) W.A. Weber ssp. parishii (A. Gray) W.A. Weber
- Seriphidium Tridentatum (Nutt.) W.A. Weber ssp. vaseyanum (Rydb.) W.A. Weber
- Seriphidium Tridentatum (Nutt.) W.A. Weber ssp. wyomingense (Beetle & Young) W.A. Weber
- Seriphidium Tripartitum (Rydb.) W.A. Weber
- Seriphidium Vaseyanum (Rydb.) W.A. Weber
- Serissa Japonica (Thunb.) Thunb.
- Serjania - Serjania Mill.
- Serkkom - Amomum Gracile Blume
- Serpent Fern - Deparia Kaalaana (Copeland) M. Kato
- Serpent Woodfern - Dryopteris Crinalis (Hook. & Arn.) C. Chr.
- Serpentine Arnica - Arnica Cernua Howell
- Serpentine Aster - Symphyotrichum Depauperatum (Fernald) G.L. Nesom
- Serpentine Bedstraw - Galium Andrewsii A. Gray ssp. gatense (Dempster) Dempster & Stebbins
- Serpentine Bird's Beak - Cordylanthus Tenuis A. Gray ssp. brunneus (Jeps.) Munz
- Serpentine Bittercress - Cardamine Pachystigma (S. Watson) Rollins
- Serpentine Bittercress - Cardamine Pachystigma (S. Watson) Rollins var. dissectifolia (Detling) Rollins
- Serpentine Bittercress - Cardamine Pachystigma (S. Watson) Rollins var. pachystigma
- Serpentine Bristleweed - Hazardia Stenolepis (H.M. Hall) Hoover
- Serpentine Collomia - Collomia Diversifolia Greene
- Serpentine Draba - Draba Oreibata J.F. Macbr. & Payson ex Payson var. serpentina Tiehm & P.K. Holm
- Serpentine Erigeron - Erigeron Serpentinus G.L. Nesom
- Serpentine Fleabane - Erigeron Angustatus Greene
- Serpentine Goldenbush - Ericameria Ophitidis (J.T. Howell) G.L. Nesom
- Serpentine Hill Raintree - Brunfelsia Densifolia Krug & Urb.
- Serpentine Indian Pink - Silene Hookeri Nutt. ssp. serpentinicola (T.W.Nelson & J.P.Nelson) K.L. Chamber
- Serpentine Jewelflower - Streptanthus Hesperidis Jeps.
- Serpentine Linanthus - Leptosiphon Ambiguus (Rattan) J.M. Porter & L.A. Johnson
- Serpentine Manjack - Cordia Bellonis Urb.
- Serpentine Manzanita - Arctostaphylos Obispoensis Eastw.
- Serpentine Milkweed - Asclepias Solanoana Woodson
- Serpentine Monardella - Monardella Purpurea Howell
- Serpentine Monkeyflower - Mimulus Brachiatus Pennell
- Serpentine Onion - Allium Diabolense (Ownbey & Aase) McNeal
- Serpentine Phacelia - Phacelia Corymbosa Jeps.
- Serpentine Pseudoleskeella Moss - Pseudoleskeella Serpentinensis P. Wilson & Norris
- Serpentine Ragwort - Packera Serpenticola Boufford, Kartesz, S.H. Shi & Renchao Zhou
- Serpentine Reedgrass - Calamagrostis Ophitidis (J.T. Howell) Nygren
- Serpentine Savory - Satureja Viminea L.
- Serpentine Sedge - Carex Serpenticola P. Zika
- Serpentine Springbeauty - Claytonia Exigua Torr. & A. Gray
- Serpentine Springbeauty - Claytonia Exigua Torr. & A. Gray ssp. exigua
- Serpentine Springbeauty - Claytonia Exigua Torr. & A. Gray ssp. glauca (Torr. & A. Gray) John M. Mill. & K.
- Serpentine Stitchwort - Minuartia Marcescens (Fernald) House
- Serpentine Sunflower - Helianthus Bolanderi A. Gray
- Serpentine Tarweed - Harmonia Doris-nilesiae (T.W. Nelson & J.P. Nelson) B.G. Baldw.
- Serpentine Wallflower Orchid - Tetramicra Canaliculata (Aubl.) Urb.
- Serpentine Wood - Rauvolfia Serpentina (L.) Benth. ex Kurz
- Serpentweed - Tonestus A. Nelson
- Serpocaulon Loriceum (L.) A.R. Sm.
- Serrasuela - Eugenia Serrasuela Krug & Urb.
- Serrate Aphanorrhegma Moss - Aphanorrhegma Serratum (Hook. f. & Wilson) Sull.
- Serrate Balsamroot - Balsamorhiza Serrata A. Nelson & J.F. Macbr.
- Serrate Dung Moss - Tayloria Serrata (Hedw.) Bruch & Schimp.
- Serrate Ephemerum Moss - Ephemerum Serratum (Hedw.) Hampe
- Serrate Funaria Moss - Funaria Serrata Brid.
- Serrate Ptychomitrium Moss - Ptychomitrium Serratum (Müll. Hal.) Bruch & Schimp.
- Serrate Spurge - Euphorbia Serrata L.
- Serrated Tussock - Nassella Trichotoma (Nees) Hack.
- Serratula Alpina L.
- Serratula Arvensis L.
- Serrette Guave - Eugenia Domingensis Berg
- Serrulate Penstemon - Penstemon Serrulatus Menzies ex Sm.
- Serviceberry - Amelanchier Medik.
- Serviceberry - Amelanchier ×intermedia Spach (pro sp.)
- Serviceberry - Amelanchier ×neglecta Eggl. ex G.N. Jones (pro sp.)
- Serviceberry - Amelanchier ×quinti-martii Louis-Marie (pro sp.)
- Sesame - Sesamum L.
- Sesame - Sesamum Orientale L.
- Sesamum Indicum L.
- Sesamum - Sesamum Alatum Thonn.
- Sesamum - Sesamum Radiatum Schumach.
- Sesban Bispinosus (Jacq.) Rydb.
- Sesban Emerus (Aubl.) Britton & P. Wilson
- Sesban Exaltatus (Raf.) Rydb.
- Sesbania Aculeata Poir.
- Sesbania Aegyptiaca (Poir.) Pers.
- Sesbania Arborea O. Deg. & I. Deg.
- Sesbania Emerus (Aubl.) Urb.
- Sesbania Exaltata (Raf.) Rydb. ex A.W. Hill
- Sesbania Exasperata Kunth
- Sesbania Hawaiiensis O. Deg. & I. Deg.
- Sesbania Hobdyi O. Deg. & I. Deg.
- Sesbania Javanica Miq.
- Sesbania Macrocarpa Muhl. ex Raf.
- Sesbania Marginata Benth.
- Sesbania Paulensis Barb. Rodr.
- Sesbania Platycarpa Pers.
- Sesbania Roxburghii Merr.
- Sesbania - Sesbania Cannabina Poir.
- Sesbania Speciosa Taub.
- Sesbania Tetraptera Hochst. ex Baker
- Sesbania Tomentosa Hook. & Arn. var. molokaiensis O. Deg. & Sherff
- Sesbania Tripetii (Poit.) hort. ex Hubb.
- Seseli - Seseli L.
- Sesleria Argentea auct.
- Sesleria Autumnalis (Scop.) F.W. Schultz
- Sesleria Caerulea (L.) Ard.
- Sesleria Cylindrica (Balb.) DC.
- Sesleria Dactyloides Nutt.
- Sesleria Elongata Host
- Sesleria Heufleriana Schur
- Sesleria Scop.
- Sesquehana Sandcherry - Prunus Susquehanae hort. ex Willd.
- Sessile Bladderpod - Lesquerella Sessilis (S. Watson) Small
- Sessile Joyweed - Alternanthera Sessilis (L.) R. Br. ex DC.
- Sessile Pterygoneurum Moss - Pterygoneurum Subsessile (Brid.) Jur.
- Sessile Skin Lichen - Leptogium Sessile Vain.
- Sessile Soot Lichen - Cyphelium Sessile (Pers.) Trevis.
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. bolanderi (A. Gray) Semple
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. echioides (Benth.) Semple
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. echioides (Benth.) Semple var. bolanderioi
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. echioides (Benth.) Semple var. camphorata
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. echioides (Benth.) Semple var. echioides
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. fastigiata (Greene) Semple
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. fastigiata (Greene) Semple var. fastigiata
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. fastigiata (Greene) Semple var. sanjacinte
- Sessileflower False Goldenaster - Heterotheca Sessiliflora (Nutt.) Shinners ssp. sessiliflora
- Sessileflower Fringetree - Chionanthus Sessiliflorus (Hemsl.) Fosberg
- Sessileflower Hoarypea - Tephrosia Sessiliflora (Poir.) Hassler
- Sessileflower Indian Parsley - Aletes Sessiliflorus W.L. Theobald & C.C. Tseng
- Sessilefruit Arrowhead - Sagittaria Rigida Pursh
- Sessileleaf Bellwort - Uvularia Sessilifolia L.
- Sessileleaf Cyanea - Cyanea Sessilifolia (O. Deg.) Lammers
- Sessileleaf False Oxtongue - Blumea Sessiliflora Decne.
- Sessileleaf Pinelandcress - Warea Sessilifolia Nash
- Sessileleaf Scurvygrass - Cochlearia Sessilifolia Rollins
- Sessileleaf Stopper - Eugenia Sessiliflora Vahl
- Sessileleaf Strap Airplant - Catopsis Sessiliflora (Ruiz & Pav.) Mez
- Sessileleaf Ticktrefoil - Desmodium Sessilifolium (Torr.) Torr. & A. Gray
- Sesuvium Erectum Correll
- Sesuvium Portulacastrum (L.) L. var. griseum O. Deg. & Fosberg
- Setaria Almaspicata de Wit
- Setaria Argentina R.A.W. Herrm.
- Setaria Carnei Hitchc.
- Setaria Chapmanii (Vasey) Pilg.
- Setaria Chevalieri Stapf & C.E. Hubb.
- Setaria Decipiens Schimp. ex Nyman
- Setaria Distans (Trin.) Veldkamp
- Setaria Firmula (Hitchc. & Chase) Pilg.
- Setaria Flabellata Stapf
- Setaria Geminata (Forssk.) Veldkamp
- Setaria Geniculata (Wild.) P. Beauv., nom. illeg.
- Setaria Germinata (Forssk.) Veldkamp var. paludivaga (Hitchc. & Chase) R. Webster
- Setaria Gerrardii Stapf
- Setaria Glauca (L.) P. Beauv.
- Setaria Glauca (L.) P. Beauv. var. pallidefusca (Schumach.) T. Koyama
- Setaria Glauca (L.) P. Beauv. var. pallidifusca (Schumach.) T. Koyama, orth. va
- Setaria Glauca sensu Vickery
- Setaria Gracilis Kunth
- Setaria Gussonei Kerguélen
- Setaria Holstii R.A.W. Herrm.
- Setaria Incrassata (Hochst.) Hack.
- Setaria Italica (L.) P. Beauv. subvar. metzgeri (Koern.) F.T. Hubbard
- Setaria Italica (L.) P. Beauv. var. metzgeri (Koern.) Jáv.
- Setaria Italica (L.) P. Beauv. var. stramineofructa (F.T. Hubbard) L.H. Bailey
- Setaria Lachnea (Nees) Kunth
- Setaria Leiophylla (Nees) Kunth
- Setaria Longiseta P. Beauv. [excluded]
- Setaria Lutescens (Weigel) F.T. Hubbard
- Setaria Pallidefusca (Schumach.) Stapf & C.E. Hubbard
- Setaria Pallidifusca (Schumach.) Stapf & C.E. Hubbard, orth. var.
- Setaria Palmifolia auct. non (J. Koenig) Stapf
- Setaria Paniculifera (Steud.) Fourn. [excluded]
- Setaria Perberbis Stapf ex de Wit
- Setaria Perennis Hack.
- Setaria Phanerococca Stapf
- Setaria Plicata (Lam.) T. Cooke
- Setaria Plicatilis (Hochst.) Hack. ex Engl.
- Setaria Poiretiana (Schult.) Kunth [excluded]
- Setaria Pumila (Poir.) Roem. & Schult. ssp. pallidifusca (Schumach.) B.K. Simon
- Setaria Ramiseta (Scribn.) Pilg.
- Setaria Sagittifolia (A. Rich.) Walp.
- Setaria Sphacelata (Schumach.) Stapf & C.E. Hubb. ex M.B. Moss var. anceps (Stapf)
- Setaria Sphacelata (Schumach.) Stapf & C.E. Hubb. ex M.B. Moss var. aurea (Hochst.
- Setaria Splendida Stapf
- Setaria Tenax (Rich.) Desv. [excluded]
- Setaria Trinervia Stapf
- Setaria Verticillata (L.) P. Beauv. var. ambigua (Guss.) Parl.
- Setaria Verticillata (L.) P. Beauv. var. respiciens (A. Rich.) A. Braun
- Setaria Viridis (L.) P. Beauv. var. ambigua (Guss.) Coss. & Durieu
- Setaria Viridis (L.) P. Beauv. var. breviseta (Döll) Hitchc.
- Setaria Viridis (L.) P. Beauv. var. robustaalba Schreib.
- Setaria Viridis (L.) P. Beauv. var. robustapurpurea Schreib.
- Setaria Viridis (L.) P. Beauv. var. weinmannii (Roem. & Schult.) Borbás
- Setaria Woodii Hack.
- Setaria ×ambigua (Guss.) Guss., nom. illeg.
- Setariopsis - Setariopsis Auriculata (Fourn.) Scribn.
- Setariopsis - Setariopsis Scribn. ex Millsp.
- Setchell's Willow - Salix Setchelliana C.R. Ball
- Setcreasea Brevifolia (Torr.) Pilg.
- Setcreasea Buckleyi I.M. Johnst.
- Setcreasea Leiandra (Torr.) Pilg.
- Setcreasea Leiandra (Torr.) Pilg. var. glandulosa Correll
- Setcreasea Ovata (J.M. Coult.) Faruqi, Celarier & Mehra
- Setcreasea Purpurea B.K. Boom
- Setiscapella Cleistogama (A. Gray) Barnhart
- Setiscapella Pusilla (Vahl) Barnhart
- Setiscapella Subulata (L.) Barnhart
- Setose Blackberry - Rubus Setosus Bigelow
- Setterwort - Helleborus Foetidus L.
- Seubertia Crocea Alph. Wood
- Seven River Hills Buckwheat - Eriogonum Gypsophilum Wooton & Standl.
- Seven Sisters - Crinum Americanum L.
- Sevenangle Pipewort - Eriocaulon Aquaticum (Hill) Druce
- Sevendevils Onion - Allium Tolmiei (Hook.) Baker ex S. Watson var. persimile Ownbey
- Sevenleaf Aganope - Aganope Heptaphylla (L.) Polhill
- Sevenleaf Creeper - Parthenocissus Heptaphylla (Buckley) Britton ex Small
- Sevennerve Roughleaf - Sagraea Scabrosa (L.) Alain
- Seventop Turnip - Brassica Septiceps (L.H. Bailey) L.H. Bailey
- Sevenyear Apple - Casasia Clusiifolia (Jacq.) Urb.
- Severinia - Severinia Ten. ex Endl.
- Sevier Canyon Stickleaf - Mentzelia Multicaulis (Osterh.) A. Nelson ex J. Darl. var. flumensevera N.H. Holmgren
- Sevier Milkvetch - Astragalus Piutensis Barneby & Mabberley
- Sevier Plateau Beardtongue - Penstemon Leptanthus Pennell
- Seward's Blackberry - Rubus Sewardianus Fernald
- Sewer Vine - Paederia Cruddasiana Prain
- Sewer Vine - Paederia L.
- Sexton Mountain Mariposa Lily - Calochortus Indecorus Ownbey & M. Peck
- Seymeria Havardii (Pennell) Standl.
- Seymeria Macrophylla Nutt.
- Shacklette's Cryptantha - Cryptantha Shackletteana Higgins
- Shaddock - Citrus Maxima (Burm. f.) Merr.
- Shade Bluebells - Mertensia Umbratilis Greenm.
- Shade Mudflower - Micranthemum Umbrosum (J.F. Gmel.) S.F. Blake
- Shade Phacelia - Phacelia Nemoralis Greene
- Shade Phacelia - Phacelia Nemoralis Greene ssp. nemoralis
- Shadow Witch - Ponthieva R. Br.
- Shadowy Goldenrod - Solidago Sciaphila Steele
- Shadscale Saltbush - Atriplex Confertifolia (Torr. & Frém.) S. Watson
- Shady Woodsorrel - Oxalis Exilis A. Cunn.
- Shafer's Hawthorn - Crataegus Shaferi Sarg.
- Shagbark Hickory - Carya Ovata (Mill.) K. Koch
- Shagbark Manzanita - Arctostaphylos Rudis Jeps. & Wies. ex Jeps.
- Shaggy Blackfoot - Melampodium Strigosum Stuessy
- Shaggy Blazing Star - Liatris Elegantula (Greene) K. Schum.
- Shaggy Blazing Star - Liatris Pilosa (Aiton) Willd.
- Shaggy Crabgrass - Digitaria Villosa (Walter) Pers.
- Shaggy Dwarf Morning-glory - Evolvulus Nuttallianus Schult.
- Shaggy Fleabane - Erigeron Pumilus Nutt.
- Shaggy Fleabane - Erigeron Pumilus Nutt. ssp. intermedius Cronquist
- Shaggy Fleabane - Erigeron Pumilus Nutt. ssp. intermedius Cronquist var. gracilior Cronquist
- Shaggy Fleabane - Erigeron Pumilus Nutt. ssp. intermedius Cronquist var. intermedius (Cronquist) Cr
- Shaggy Fleabane - Erigeron Pumilus Nutt. ssp. pumilus
- Shaggy Hedgehyssop - Gratiola Pilosa Michx.
- Shaggy Lupine - Lupinus Covillei Greene
- Shaggy Milkvetch - Astragalus Malacus A. Gray
- Shaggy Soldier - Galinsoga Quadriradiata Cav.
- Shaggyfruit Pepperweed - Lepidium Lasiocarpum Nutt.
- Shaggyfruit Pepperweed - Lepidium Lasiocarpum Nutt. var. lasiocarpum
- Shaggyhair Alumroot - Heuchera Hirsutissima Rosend., Butters & Lakela
- Shaggyhair Lupine - Lupinus Spectabilis Hoover
- Shaggystem Cyrtandra - Cyrtandra Oenobarba H. Mann
- Shaggytuft - Stenandrium Nees
- Shakeshake - Crotalaria Incana L.
- Shale Barren Buckwheat - Eriogonum Allenii S. Watson
- Shale Barren Evening Primrose - Oenothera Argillicola Mack.
- Shale Barren Pussytoes - Antennaria Virginica Stebbins
- Shale Barren Ragwort - Packera Antennariifolia (Britton) W.A. Weber & Á. Löve
- Shale Barren Rockcress - Arabis Serotina Steele
- Shallow Sedge - Carex Lurida Wahlenb.
- Shamel Ash - Fraxinus Uhdei (Wenzig) Lingelsh.
- Shameplant - Mimosa Pudica L.
- Shameplant - Mimosa Pudica L. var. pudica
- Shameplant - Mimosa Pudica L. var. unijuga (Duchass. & Walp.) Griseb.
- Sharktail Cyanea - Cyanea Pinnatifida (Cham.) E. Wimm.
- Sharp Blazing Star - Liatris Acidota Engelm. & A. Gray
- Sharp Brake - Pteris Pungens Willd.
- Sharp Cupgrass - Eremochloa Leersioides (Munro) Hack.
- Sharp's Club Lichen - Multiclavula Sharpii R. Petersen
- Sharp's Homaliadelphus Moss - Homaliadelphus Sharpii (R.S. Williams) Sharp
- Sharp's Leptohymenium Moss - Leptohymenium Sharpii (H.A. Crum & L.E. Anderson) W.R. Buck & H.A. Crum
- Sharp's Mock Orange - Philadelphus Sharpianus Hu
- Sharp's Weissia Moss - Weissia Sharpii L.E. Anderson & Lemmon
- Sharp-leaf Spiderling - Boerhavia Acutifolia (Choisy) J.W. Moore
- Sharp-stipule Willow - Salix ×mollissima Ehrh.
- Sharp-tooth Buckthorn - Rhamnus Arguta Maxim.
- Sharp-tooth Buckthorn - Rhamnus Arguta Maxim. var. velutina Hand.-Maz.
- Sharp-tooth Clover - Trifolium Argutum Banks & Sol.
- Sharpflower Rush - Juncus Acutiflorus Ehrh.
- Sharpglume Brome - Bromus Mucroglumis Wagnon
- Sharpiella Seligeri (Brid.) Z. Iwats.
- Sharpiella Striatella (Brid.) Z. Iwats.
- Sharpiella Turfacea (Lindb.) Z. Iwats.
- Sharpkeel Milkvetch - Astragalus Acutirostris S. Watson
- Sharpleaf Baby's-breath - Gypsophila Acutifolia Stev. ex Spreng.
- Sharpleaf Buttercup - Ranunculus Acriformis A. Gray
- Sharpleaf Buttercup - Ranunculus Acriformis A. Gray var. acriformis
- Sharpleaf Cancerwort - Kickxia Elatine (L.) Dumort.
- Sharpleaf Groundcherry - Physalis Acutifolia (Miers) Sandw.
- Sharpleaf Gumweed - Grindelia Acutifolia Steyerm.
- Sharpleaf Hookeria Moss - Hookeria Acutifolia Hook. & Grev.
- Sharpleaf Penstemon - Penstemon Acuminatus Douglas ex Lindl.
- Sharpleaf Penstemon - Penstemon Acuminatus Douglas ex Lindl. var. acuminatus
- Sharpleaf Penstemon - Penstemon Acuminatus Douglas ex Lindl. var. latebracteatus N.H. Holmgren
- Sharpleaf Silverbush - Argythamnia Candicans Sw.
- Sharpleaf Snowberry - Symphoricarpos Acutus (A. Gray) Dieck
- Sharpleaf St. Johnswort - Hypericum Virgatum Lam.
- Sharpleaf Twinpod - Physaria Acutifolia Rydb.
- Sharpleaf Twinpod - Physaria Acutifolia Rydb. var. acutifolia
- Sharpleaf Twinpod - Physaria Acutifolia Rydb. var. purpurea S.L. Welsh & Reveal
- Sharpleaf Valerian - Valeriana Acutiloba Rydb.
- Sharpleaf Valerian - Valeriana Acutiloba Rydb. var. acutiloba
- Sharplobe Hepatica - Hepatica Nobilis Schreb. var. acuta (Pursh) Steyerm.
- Sharplobe St. Johnswort - Hypericum Harperi R. Keller
- Sharpnut Cryptantha - Cryptantha Oxygona (A. Gray) Greene
- Sharppod Rushpea - Hoffmannseggia Oxycarpa Benth. ex A. Gray
- Sharpscale Bulrush - Schoenoplectiella Erecta (Poir.) Lye
- Sharpscale Bulrush - Schoenoplectiella Erecta (Poir.) Lye ssp. raynalii (Schuyler) Beentje
- Sharpscale Flatsedge - Cyperus Oxylepis Nees ex Steud.
- Sharpscale Sedge - Carex Oxylepis Torr. & Hook.
- Sharpscale Sedge - Carex Oxylepis Torr. & Hook. var. oxylepis
- Sharpscale Sedge - Carex Oxylepis Torr. & Hook. var. pubescens J.K. Underw.
- Sharpscale Spikerush - Eleocharis Compressa Sull. var. acutisquamata (Buckley) S.G. Sm.
- Sharpsepal Beardtongue - Penstemon Tenuis Small
- Sharptip Sandwort - Arenaria Congesta Nutt. var. cephaloidea (Rydb.) Maguire
- Sharptooth Blacksnakeroot - Sanicula Arguta Greene ex J.M. Coult. & Rose
- Sharpwing Monkeyflower - Mimulus Alatus Aiton
- Sharsmith's Draba - Draba Sharsmithii Rollins & R.A. Price
- Sharsmith's Onion - Allium Sharsmithiae (Ownbey & Aase) McNeal
- Sharsmith's Stickseed - Hackelia Sharsmithii I.M. Johnst.
- Shasta Beardtongue - Penstemon Heterodoxus A. Gray var. shastensis (D.D. Keck) N.H. Holmgren
- Shasta Buckwheat - Eriogonum Pyrolifolium Hook.
- Shasta Buckwheat - Eriogonum Pyrolifolium Hook. var. coryphaeum Torr. & A. Gray
- Shasta Buckwheat - Eriogonum Pyrolifolium Hook. var. pyrolifolium
- Shasta Chaenactis - Chaenactis Suffrutescens A. Gray
- Shasta Clarkia - Clarkia Borealis E. Small ssp. arida E. Small
- Shasta Clover - Trifolium Productum Greene
- Shasta County Arnica - Arnica Venosa H.M. Hall
- Shasta Helianthella - Helianthella Californica A. Gray ssp. shastensis (W.A. Weber) W.A. Weber
- Shasta Knotweed - Polygonum Shastense W.H. Brewer
- Shasta Lecania Lichen - Lecania Shastensis Herre
- Shasta Lily - Lilium Pardalinum Kellogg ssp. shastense (Eastw.) M.W. Skinner
- Shasta Lupine - Lupinus Albicaulis Douglas var. shastensis (A. Heller) C.P. Sm.
- Shasta Maidenhair - Adiantum Shastense Huiet & A.R. Sm.
- Shasta Owl's-clover - Orthocarpus Pachystachyus A. Gray
- Shasta Panicgrass - Dichanthelium ×scoparioides (Ashe) Mohlenbr. (pro sp.)
- Shasta Popcornflower - Plagiobothrys Shastensis Greene ex A. Gray
- Shasta Red Fir - Abies Magnifica A. Murray bis var. shastensis Lemmon
- Shasta River Mariposa Lily - Calochortus Monanthus Ownbey
- Shasta Sedge - Carex Straminiformis L.H. Bailey
- Shasta Snakeroot - Ageratina Shastensis (D.W. Taylor & Stebbins) R.M. King & H. Rob.
- Shasta Snow-wreath - Neviusia Cliftonii Shevock, Ertter & D.W. Taylor
- Shasta Tansyaster - Machaeranthera Canescens (Pursh) A. Gray ssp. canescens var. shastensis (A. Gray) B.L. Tu
- Shasta Tarweed - Madia Citrigracilis D.D. Keck
- Shaved Sedge - Carex Tonsa (Fernald) E.P. Bicknell
- Shaved Sedge - Carex Tonsa (Fernald) E.P. Bicknell var. tonsa
- Shea Butter - Vitellaria Paradoxa C.F. Gaertn.
- Sheathed Alkaligrass - Puccinellia Vaginata (Lange) Fernald & Weath.
- Sheathed Deathcamas - Zigadenus Vaginatus (Rydb.) J.F. Macbr.
- Sheathed Pondweed - Stuckenia Vaginata (Turcz.) Holub
- Sheathed Sedge - Carex Vaginata Tausch
- Sheathed Wildparsley - Musineon Vaginatum Rydb.
- Sheep Cinquefoil - Potentilla Ovina Macoun ex J.M. Macoun
- Sheep Cinquefoil - Potentilla Ovina Macoun ex J.M. Macoun var. decurrens (S. Watson) S.L. Welsh & B.
- Sheep Cinquefoil - Potentilla Ovina Macoun ex J.M. Macoun var. ovina
- Sheep Fescue - Festuca Ovina L.
- Sheep Fleabane - Erigeron Ovinus Cronquist
- Sheep Laurel - Kalmia Angustifolia L.
- Sheep Milkvetch - Astragalus Nothoxys A. Gray
- Sheep Sedge - Carex Illota L.H. Bailey
- Sheepbit - Jasione Montana L.
- Sheldon's Milkvetch - Astragalus Sheldonii (Rydb.) Barneby
- Sheldon's Sedge - Carex Sheldonii Mack.
- Shell Lichen - Arthopyrenia A. Massal.
- Shell Lichen - Arthopyrenia Cerasi (Schrad.) A. Massal.
- Shell Lichen - Arthopyrenia Cinereopruinosa (Schaerer) A. Massal.
- Shell Lichen - Arthopyrenia Majuscula (Nyl.) Zahlbr.
- Shell Lichen - Arthopyrenia Malaccitula (Nyl.) Zahlbr.
- Shell Lichen - Arthopyrenia Minor R.C. Harris
- Shell Lichen - Arthopyrenia Planorbis (Ach.) Müll. Arg.
- Shell Lichen - Arthopyrenia Plumbaria (Stizenb.) R.C. Harris
- Shellbark Hickory - Carya Laciniosa (Michx. f.) G. Don
- Shellflower - Moluccella Laevis L.
- Shellplant - Alpinia Zerumbet (Pers.) B.L. Burtt & R.M. Sm.
- Shelly's Mousetail - Ivesia Rhypara Ertter & Reveal var. shellyi Ertter
- Shelton's Monardella - Monardella Sheltonii (Torr.) Howell
- Shelton's Violet - Viola Sheltonii Torr.
- Shenandoah Pore Lichen - Pertusaria Shenandoensis Hale & Dibben
- Sheoak - Casuarina Rumph. ex L.
- Shepardscress - Teesdalia W.t. Aiton
- Shepherd's Purse - Capsella Bursa-pastoris (L.) Medik.
- Shepherdsneedle - Scandix Pecten-veneris L.
- Sherard's Downy Rose - Rosa Sherardii Davies
- Sherardia - Sherardia L.
- Sherman Hoyt Woolstar - Eriastrum Pluriflorum (A. Heller) H. Mason ssp. sherman-hoytae (Craig) H. Mason
- Sherring's Cup Orchid - Brachionidium Sherringii Rolfe
- Sherring's Dwarf Polypody - Grammitis Sherringii (Baker) Proctor
- Sherwoodia Galacifolia (Torr. & A. Gray) House
- Shibataea Makino ex Nakai
- Shield Aralia - Polyscias Scutellaria (Burm. f.) Fosberg
- Shield Clover - Trifolium Clypeatum L.
- Shield Clover - Trifolium Scutatum Boiss.
- Shield Lichen - Heterodermia Albicans (Pers.) Swinscow & Krog
- Shield Lichen - Heterodermia Chondroidea W.A. Weber & D.D. Awasthi
- Shield Lichen - Heterodermia Diademata (Taylor) D.D. Awasthi
- Shield Lichen - Heterodermia Echinata (Taylor) W.L. Culb.
- Shield Lichen - Heterodermia Erinacea (Ach.) W.A. Weber
- Shield Lichen - Heterodermia Galactophylla (Tuck.) W.L. Culb.
- Shield Lichen - Heterodermia Granulifera (Ach.) W.L. Culb.
- Shield Lichen - Heterodermia Hypoleuca (Muhl.) Trevis.
- Shield Lichen - Heterodermia Leucomelos (L.) Poelt
- Shield Lichen - Heterodermia Pseudospeciosa (Kurok.) W.L. Culb.
- Shield Lichen - Heterodermia Speciosa (Wulfen) Trevis.
- Shield Lichen - Heterodermia Squamulosa (Degel.) W.L. Culb.
- Shield Lichen - Heterodermia Trevis.
- Shield Lichen - Parmelia Ach.
- Shield Lichen - Parmelia Fertilis Müll. Arg.
- Shield Lichen - Parmelia Fraudans (Nyl.) Nyl.
- Shield Lichen - Parmelia Hygrophila Goward & Ahti
- Shield Lichen - Parmelia Neodiscordans Hale
- Shield Lichen - Parmelia Omphalodes (L.) Ach.
- Shield Lichen - Parmelia Omphalodes (L.) Ach. ssp. omphalodes
- Shield Lichen - Parmelia Saxatilis (L.) Ach.
- Shield Lichen - Parmelia Squarrosa Hale
- Shield Lichen - Parmelia Sulcata Taylor
- Shield Nasturtium - Tropaeolum Peltophorum Benth.
- Shieldbract Monkeyflower - Mimulus Glaucescens Greene
- Shieldfern - Lastreopsis Ching
- Shieldplant - Streptanthus Tortuosus Kellogg
- Shieldplant - Streptanthus Tortuosus Kellogg var. flavescens Jeps.
- Shieldplant - Streptanthus Tortuosus Kellogg var. optatus Jeps.
- Shieldplant - Streptanthus Tortuosus Kellogg var. orbiculatus (Greene) H.M. Hall
- Shieldplant - Streptanthus Tortuosus Kellogg var. pallidus Jeps.
- Shieldplant - Streptanthus Tortuosus Kellogg var. suffrutescens (Greene) Jeps.
- Shieldplant - Streptanthus Tortuosus Kellogg var. tortuosus
- Shieldpod - Dithyrea Harv.
- Shineseed - Rousselia Humilis (Sw.) Urb.
- Shingle Flatsedge - Cyperus Imbricatus Retz.
- Shingle Oak - Quercus Imbricaria Michx.
- Shingleplant - Marcgravia Sintenisii Urb.
- Shinglewood - Nectandra Hihua (Ruiz & Pav.) Rohwer
- Shining Alkaligrass - Puccinellia Lucida Fernald & Weath.
- Shining Bedstraw - Galium Concinnum Torr. & A. Gray
- Shining Bird Of Paradise - Heliconia Metallica Planch. & Linden ex Hook.
- Shining Blazingstar - Mentzelia Nitens Greene
- Shining Blazingstar - Mentzelia Nitens Greene var. nitens
- Shining Clubmoss - Huperzia Lucidula (Michx.) Trevis.
- Shining False Indigo - Amorpha Nitens Boynt.
- Shining Fleabane - Erigeron Barbellulatus Greene
- Shining Geranium - Geranium Lucidum L.
- Shining Gum - Eucalyptus Nitens (H. Deane & Maiden) Maiden
- Shining Lady's Tresses - Spiranthes Lucida (H.H. Eaton) Ames
- Shining Milkwort - Polygala Nitida Brandegee
- Shining Milkwort - Polygala Nitida Brandegee var. goliadensis T. Wendt
- Shining Milkwort - Polygala Nitida Brandegee var. nitida Brandegee [excluded]
- Shining Milkwort - Polygala Nitida Brandegee var. tamaulipana T. Wendt
- Shining Netvein Barberry - Mahonia Dictyota (Jeps.) Fedde
- Shining Pepperweed - Lepidium Nitidum Nutt.
- Shining Pepperweed - Lepidium Nitidum Nutt. var. nitidum
- Shining Pepperweed - Lepidium Nitidum Nutt. var. oreganum (Howell ex Greene) C.L. Hitchc.
- Shining Rose - Rosa Nitida Willd.
- Shining Spurge - Euphorbia Lucida Waldst. & Kit.
- Shining Willow - Salix Lucida Muhl.
- Shining Willow - Salix Lucida Muhl. ssp. lucida
- Shiningbranch Hawthorn - Crataegus Corusca Sarg.
- Shinner's Sedge - Carex Shinnersii P. Rothr. & Reznicek
- Shinnersia Rivularis (A. Gray) R.M. King & H. Rob.
- Shiny Biscuitroot - Lomatium Lucidum (Nutt. ex Torr. & A. Gray) Jeps.
- Shiny Blueberry - Vaccinium Myrsinites Lam.
- Shiny Bugseed - Corispermum Nitidum Kit. ex Schult. [excluded]
- Shiny Chickweed - Stellaria Nitens Nutt.
- Shiny Coneflower - Rudbeckia Nitida Nutt.
- Shiny Cotoneaster - Cotoneaster Lucidus Schltdl.
- Shiny Goldenrod - Oligoneuron Nitidum (Torr. & A. Gray) Small
- Shiny Necklace Fern - Lindsaea Lucida Blume
- Shiny Wedgescale - Sphenopholis Nitida (Biehler) Scribn.
- Shiny Woodoats - Chasmanthium Nitidum (Baldw.) Yates
- Shiny-leaf Yellow Loosestrife - Lysimachia Scopulensis Marr
- Shiny-nutlet Popcornflower - Plagiobothrys Nitens (Greene) I.M. Johnst.
- Shinyfruit Popcornflower - Plagiobothrys Lamprocarpus (Piper) I.M. Johnst.
- Shinyleaf Currant - Ribes Cruentum Greene
- Shinyleaf Currant - Ribes Cruentum Greene var. cruentum
- Shinyleaf Meadowsweet - Spiraea Corymbosa Raf.
- Shinyleaf Sandpaper Plant - Petalonyx Nitidus S. Watson
- Shinyleaf Spirea - Spiraea Lucida Douglas ex Greene
- Shinystem Spleenwort - Asplenium Uniseriale Raddi
- Shipman's Cyanea - Cyanea Shipmanii Rock
- Shirakiopsis - Shirakiopsis Esser
- Shirley Meadows Mariposa Lily - Calochortus Westonii Eastw.
- Shoals Spiderlily - Hymenocallis Coronaria (Leconte) Kunth
- Shoalweed - Halodule Wrightii Asch.
- Shockley's Buckwheat - Eriogonum Shockleyi S. Watson
- Shockley's Desert-thorn - Lycium Shockleyi A. Gray
- Shockley's Evening Primrose - Camissonia Heterochroma (S. Watson) P.H. Raven
- Shockley's Goldenhead - Acamptopappus Shockleyi A. Gray
- Shockley's Milkvetch - Astragalus Serenoi (Kuntze) Sheldon var. shockleyi (M.E. Jones) Barneby
- Shockley's Rockcress - Arabis Shockleyi Munz
- Shoeblackplant - Hibiscus Rosa-sinensis L.
- Shoebutton - Ardisia Elliptica Thunb.
- Shoestring Fern - Vittaria Lineata (L.) Sm.
- Shoestring Fern - Vittaria Sm.
- Shoofly - Caesalpinia Decapetala (Roth) Alston
- Shootingstar - Dodecatheon L.
- Shore Aster - Symphyotrichum Tradescantii (L.) G.L. Nesom
- Shore Juniper - Juniperus Conferta Parl.
- Shore Little Bluestem - Schizachyrium Littorale (Nash) E.P. Bicknell
- Shore Quillwort - Isoetes Riparia Engelm. ex A. Braun
- Shore Quillwort - Isoetes Riparia Engelm. ex A. Braun var. riparia
- Shorea - Shorea Roxb. ex C.F. Gaertn.
- Shoregrass - Monanthochloe Engelm.
- Shoregrass - Monanthochloe Littoralis Engelm.
- Shoreline Figwort - Scrophularia Auriculata L.
- Shoreline Seapurslane - Sesuvium Portulacastrum (L.) L.
- Shoreline Seapurslane - Sesuvium Portulacastrum (L.) L. var. portulacastrum
- Shoreline Sedge - Carex Hyalinolepis Steud.
- Short Bluegrass - Poa Abbreviata R. Br.
- Short Bluegrass - Poa Abbreviata R. Br. ssp. abbreviata
- Short Lupine - Lupinus Brevior (Jeps.) Christian & D. Dunn
- Short Muhly - Muhlenbergia Brevis C.O. Goodding
- Short Wingcup - Schultesia Brachyptera Cham.
- Short Woollyheads - Psilocarphus Brevissimus Nutt.
- Short Woollyheads - Psilocarphus Brevissimus Nutt. var. brevissimus
- Short's Aster - Symphyotrichum Shortii (Lindl.) G.L. Nesom
- Short's Goldenrod - Solidago Shortii Torr. & A. Gray
- Short's Hedgehyssop - Gratiola Viscidula Pennell
- Short's Milkvetch - Astragalus Shortianus Nutt.
- Short's Rockcress - Arabis Shortii (Fernald) Gleason
- Short's Sedge - Carex Shortiana Dewey
- Short's Spreading Chervil - Chaerophyllum Procumbens (L.) Crantz var. shortii Torr. & A. Gray
- Short-hair Cottongrass - Calliscirpus Brachythrix C.N. Gilmour, J.R. Starr & Naczi
- Short-lobe Indian Paintbrush - Castilleja Hispida Benth. ssp. brevilobata (Piper) T.I. Chuang & Heckard
- Short-rayed Alkali Aster - Symphyotrichum Frondosum (Nutt.) G.L. Nesom
- Short-spike Peperomia - Peperomia Parvulifolia Trel.
- Shortawn Foxtail - Alopecurus Aequalis Sobol.
- Shortawn Foxtail - Alopecurus Aequalis Sobol. var. aequalis
- Shortbeak Arrowhead - Sagittaria Brevirostra Mack. & Bush
- Shortbeak Beaksedge - Rhynchospora Nitens (Vahl) A. Gray
- Shortbeak Sedge - Carex Brevior (Dewey) Mack.
- Shortbeard Plumegrass - Saccharum Brevibarbe (Michx.) Pers.
- Shortbeard Plumegrass - Saccharum Brevibarbe (Michx.) Pers. var. brevibarbe
- Shortbristle Beaksedge - Rhynchospora Galeana Naczi, W.M. Knapp & Gerry Moore
- Shortbristle Horned Beaksedge - Rhynchospora Corniculata (Lam.) A. Gray
- Shortbristle Needle And Thread - Hesperostipa Curtiseta (Hitchc.) Barkworth
- Shortbristled Needlegrass - Achnatherum Brachychaetum (Godr.) Barkworth
- Shortcoal Bluegrass - Poa Pseudoabbreviata Rosh.
- Shortcrown Milkvine - Matelea Brevicoronata (B.L. Rob.) Woodson
- Shortflower Buckwheat - Eriogonum Brachyanthum Coville
- Shortflower Indian Paintbrush - Castilleja Puberula Rydb.
- Shortflower Monkeyflower - Mimulus Breviflorus Piper
- Shortflower Rattlebox - Crotalaria Breviflora DC.
- Shortflowered Bog Orchid - Platanthera Brevifolia (Greene) Kranzlin
- Shortfruit Evening Primrose - Oenothera Brachycarpa A. Gray
- Shortfruit Hedgemustard - Sisymbrium Polyceratium L.
- Shortfruit Spikerush - Eleocharis Brachycarpa Svens.
- Shortfruit Stork's Bill - Erodium Brachycarpum (Godr.) Thell.
- Shortfruit Willow - Salix Brachycarpa Nutt.
- Shortfruit Willow - Salix Brachycarpa Nutt. var. brachycarpa
- Shortfruit Willow - Salix Brachycarpa Nutt. var. psammophila Raup
- Shorthair Goldenrod - Solidago Canadensis L. var. gilvocanescens Rydb.
- Shorthair Reedgrass - Calamagrostis Breweri Thurb.
- Shorthair Sedge - Carex Exserta Mack.
- Shorthook Fishhook Cactus - Ancistrocactus Brevihamatus (Engelm.) Britton & Rose
- Shorthook Fishhook Cactus - Ancistrocactus Brevihamatus (Engelm.) Britton & Rose var. brevihamatus
- Shorthook Fishhook Cactus - Ancistrocactus Brevihamatus (Engelm.) Britton & Rose var. pallidus A.D. Zimmerman ex A.M. Po
- Shorthook Fishhook Cactus - Ancistrocactus Tobuschii (W.T. Marshall) W.T. Marshall ex Backeb.
- Shorthorn Steer's-head - Dicentra Pauciflora S. Watson
- Shorthusk - Brachyelytrum P. Beauv.
- Shortia - Shortia Torr. & A. Gray
- Shortleaf Alpinegold - Hulsea Brevifolia A. Gray
- Shortleaf Baccharis - Baccharis Brachyphylla A. Gray
- Shortleaf Blazing Star - Liatris Tenuifolia Nutt.
- Shortleaf Blazing Star - Liatris Tenuifolia Nutt. var. quadriflora Chapm.
- Shortleaf Blazing Star - Liatris Tenuifolia Nutt. var. tenuifolia
- Shortleaf Bruchia Moss - Bruchia Brevifolia Sull.
- Shortleaf Crabgrass - Digitaria Hitchcockii (Chase) Stuckert
- Shortleaf Dicranum Moss - Dicranum Brevifolium (Lindb.) Lindb.
- Shortleaf Drepanocladus Moss - Drepanocladus Brevifolius (Lindb.) Warnst.
- Shortleaf Dwarf-cudweed - Hesperevax Sparsiflora (A. Gray) Greene var. brevifolia (A. Gray) Morefield
- Shortleaf Jefea - Jefea Brevifolia (A. Gray) Strother
- Shortleaf Liveforever - Dudleya Blochmaniae (Eastw.) Moran ssp. brevifolia (Moran) Moran
- Shortleaf Lobelia - Lobelia Brevifolia Nutt. ex A. DC.
- Shortleaf Pine - Pinus Echinata Mill.
- Shortleaf Rose Gentian - Sabatia Brevifolia Raf.
- Shortleaf Skeletongrass - Gymnopogon Brevifolius Trin.
- Shortleaf Small Limestone Moss - Seligeria Brevifolia (Lindb.) Lindb.
- Shortleaf Sneezeweed - Helenium Brevifolium (Nutt.) Alph. Wood
- Shortleaf Spikesedge - Kyllinga Brevifolia Rottb.
- Shortleaf Stopper - Eugenia Apiculata DC.
- Shortleaf Sunflower - Helianthus ×brevifolius E.E. Watson (pro sp.)
- Shortleaf Trichostomopsis Moss - Trichostomopsis Brevifolia E.B. Bartram
- Shortleaf Wild Coffee - Psychotria Tenuifolia Sw.
- Shortleaf Woollygrass - Erioneuron Avenaceum (Kunth) Tateoka
- Shortleaf Yelloweyed Grass - Xyris Brevifolia Michx.
- Shortleaved Sedge - Carex Misandra R. Br.
- Shortlobe Penstemon - Penstemon Seorsus (A. Nelson) D.D. Keck
- Shortlobe Phacelia - Phacelia Brachyloba (Benth.) A. Gray
- Shortpod Draba - Draba Brachycarpa Nutt. ex Torr. & A. Gray
- Shortpod Mustard - Hirschfeldia Incana (L.) Lagr.-Foss.
- Shortpod Thelypody - Thelypodium Brachycarpum Torr.
- Shortray Fleabane - Erigeron Lonchophyllus Hook.
- Shortray Rockdaisy - Perityle Microglossa Benth.
- Shortray Zinnia - Zinnia Anomala A. Gray
- Shortseed Waterwort - Elatine Brachysperma A. Gray
- Shortsepal Lewisia - Lewisia Brachycalyx Engelm. ex A. Gray
- Shortspike Bluestem - Andropogon Brachystachyus Chapm.
- Shortspike Canarygrass - Phalaris Brachystachys Link
- Shortspike Hedgenettle - Stachys Pycnantha Benth.
- Shortspike Noseburn - Tragia Brevispica Engelm. & A. Gray
- Shortspike Watermilfoil - Myriophyllum Sibiricum Kom.
- Shortspike Windmill Grass - Chloris ×subdolichostachya Müll. Berol. (pro sp.)
- Shortspine Horsebrush - Tetradymia Spinosa Hook. & Arn.
- Shortspur Seablush - Plectritis Congesta (Lindl.) DC.
- Shortspur Seablush - Plectritis Congesta (Lindl.) DC. ssp. brachystemon (Fisch. & C.A. Mey.) Morey
- Shortspur Seablush - Plectritis Congesta (Lindl.) DC. ssp. congesta
- Shortspur Seablush - Plectritis Congesta (Lindl.) DC. ssp. nitida (A. Heller) Morey
- Shortstalk Bristle Fern - Trichomanes Brevipes (C. Presl) Baker
- Shortstalk Chickweed - Cerastium Brachypodum (Engelm. ex A. Gray) B.L. Rob.
- Shortstalk Dewberry - Rubus Curtipes L.H. Bailey
- Shortstalk False Bindweed - Calystegia Silvatica (Kit.) Griseb.
- Shortstalk False Bindweed - Calystegia Silvatica (Kit.) Griseb. ssp. disjuncta Brummitt
- Shortstalk False Bindweed - Calystegia Silvatica (Kit.) Griseb. ssp. fraterniflora (Mack. & Bush) Brummitt
- Shortstalk False Bindweed - Calystegia Silvatica (Kit.) Griseb. ssp. silvatica
- Shortstalk Forchhammeria - Forchhammeria Brevipes Urb.
- Shortstalk Sedge - Carex Podocarpa R. Br.
- Shortstalk Stinkweed - Cleomella Brevipes S. Watson
- Shortstem Beardtongue - Penstemon Breviculus (D.D. Keck) Nisbet & R.C. Jacks.
- Shortstem Buckwheat - Eriogonum Brevicaule Nutt.
- Shortstem Buckwheat - Eriogonum Brevicaule Nutt. var. brevicaule
- Shortstem Buckwheat - Eriogonum Brevicaule Nutt. var. laxifolium (Torr. & A. Gray) Reveal
- Shortstem Buckwheat - Eriogonum Brevicaule Nutt. var. micranthum (Nutt.) Reveal
- Shortstem Lupine - Lupinus Brevicaulis S. Watson
- Shortstem Philodendron - Philodendron Fragrantissimum (Hook.) G. Don
- Shortstem Sedge - Carex Brevicaulis Mack.
- Shortstyle Bluebells - Mertensia Brevistyla S. Watson
- Shortstyle Draba - Draba Brachystylis Rydb.
- Shortstyle Indian Paintbrush - Castilleja Brevistyla (Hoover) T.I. Chuang & Heckard
- Shortstyle Onion - Allium Brevistylum S. Watson
- Shorttooth Canadian Milkvetch - Astragalus Canadensis L. var. brevidens (Gandog.) Barneby
- Shoshone Carrot - Shoshonea Pulvinata Evert & Constance
- Shoshone Ricegrass - Piptatheropsis Shoshoneana (Curto & Douglass M. Hend.) Romasch., P.M. Peterson & R.J. Soren
- Shoshonea - Shoshonea Evert & Constance
- Showman's Hypotrachyna Lichen - Hypotrachyna Showmanii Hale
- Showy Alpine Forget-me-not - Eritrichium Splendens Kearney
- Showy Alpine Ragwort - Senecio Amplectens A. Gray
- Showy Alpine Ragwort - Senecio Amplectens A. Gray var. amplectens
- Showy Baby's-breath - Gypsophila Elegans M. Bieb.
- Showy Balloonvine - Cardiospermum Grandiflorum Sw.
- Showy Blackberry - Rubus Elegantulus Blanch.
- Showy Buttercup - Ranunculus Acris L. var. acris
- Showy Cappel - Palicourea Guianensis Aubl.
- Showy Cappel - Palicourea Guianensis Aubl. ssp. barbinervia (DC.) Steyerm.
- Showy Chalicevine - Solandra Grandiflora Sw.
- Showy Colchicum - Colchicum Speciosum Steven
- Showy Combretum - Combretum Grandiflorum G. Don
- Showy Coneflower - Rudbeckia Alpicola Piper
- Showy Dandelion - Taraxacum Spectabile Dahlst.
- Showy Dawnflower - Stylisma Abdita Myint
- Showy Dewflower - Drosanthemum Floribundum (Haw.) Schwant.
- Showy Draba - Draba Spectabilis Greene
- Showy Draba - Draba Spectabilis Greene var. oxyloba (Greene) Gilg & Schulz ex O.E. Schulz
- Showy Draba - Draba Spectabilis Greene var. spectabilis
- Showy Evening Primrose - Oenothera Grandis (Britton) Smyth
- Showy False Dragonhead - Physostegia Pulchella Lundell
- Showy Fanpetals - Sida Lindheimeri Engelm. & A. Gray
- Showy Fly Honeysuckle - Lonicera ×bella Zabel
- Showy Forsythia - Forsythia ×intermedia Zabel
- Showy Gentian - Gentiana Decora Pollard
- Showy Gilia - Gilia Cana (M.E. Jones) A. Heller
- Showy Gilia - Gilia Cana (M.E. Jones) A. Heller ssp. bernardina A.D. Grant & V.E. Grant
- Showy Gilia - Gilia Cana (M.E. Jones) A. Heller ssp. cana
- Showy Gilia - Gilia Cana (M.E. Jones) A. Heller ssp. speciformis A.D. Grant & V.E. Grant
- Showy Gilia - Gilia Cana (M.E. Jones) A. Heller ssp. speciosa (Jeps.) A.D. Grant & V.E. G
- Showy Gilia - Gilia Cana (M.E. Jones) A. Heller ssp. triceps (Brand) A.D. Grant & V.E. Gr
- Showy Goldenbanner - Thermopsis Robusta Howell
- Showy Goldeneye - Heliomeris Multiflora Nutt.
- Showy Goldeneye - Heliomeris Multiflora Nutt. var. brevifolia (Greene ex Wooton & Standl.) Yates
- Showy Goldeneye - Heliomeris Multiflora Nutt. var. macrocephala Heiser
- Showy Goldeneye - Heliomeris Multiflora Nutt. var. multiflora
- Showy Goldenrod - Solidago Erecta Pursh
- Showy Goldenrod - Solidago Speciosa Nutt.
- Showy Goldenrod - Solidago Speciosa Nutt. var. jejunifolia (Steele) Cronquist
- Showy Goldenrod - Solidago Speciosa Nutt. var. pallida Porter
- Showy Goldenrod - Solidago Speciosa Nutt. var. rigidiuscula Torr. & A. Gray
- Showy Goldenrod - Solidago Speciosa Nutt. var. speciosa
- Showy Greenbright - Gambelia Speciosa Nutt.
- Showy Indian Clover - Trifolium Amoenum Greene
- Showy Lady's Slipper - Cypripedium Reginae Walter
- Showy Locoweed - Oxytropis Splendens Douglas ex Hook.
- Showy Maiden Fern - Thelypteris Puberula (Baker) Morton
- Showy Medinilla - Medinilla Magnifica Lindl.
- Showy Menodora - Menodora Longiflora A. Gray
- Showy Milkweed - Asclepias Speciosa Torr.
- Showy Milkwort - Polygala Grandiflora Walter
- Showy Milkwort - Polygala Grandiflora Walter var. angustifolia Torr. & A. Gray
- Showy Milkwort - Polygala Grandiflora Walter var. grandiflora
- Showy Mullein - Verbascum Speciosum Schrad.
- Showy Nerveray - Tetragonotheca Repanda (Buckley) Small
- Showy Orchid - Galearis Spectabilis (L.) Raf.
- Showy Penstemon - Penstemon Spectabilis Thurb. ex A. Gray
- Showy Penstemon - Penstemon Spectabilis Thurb. ex A. Gray ssp. spectabilis
- Showy Penstemon - Penstemon Spectabilis Thurb. ex A. Gray ssp. subviscosus D.D. Keck
- Showy Phlox - Phlox Speciosa Pursh
- Showy Phlox - Phlox Speciosa Pursh ssp. lanceolata (E.E. Nelson) Wherry
- Showy Phlox - Phlox Speciosa Pursh ssp. lignosa Brand
- Showy Phlox - Phlox Speciosa Pursh ssp. nitida (Suksd.) Wherry
- Showy Phlox - Phlox Speciosa Pursh ssp. occidentalis (Durand ex Torr.) Wherry
- Showy Phlox - Phlox Speciosa Pursh ssp. speciosa
- Showy Pigeonpea - Cajanus Scarabaeoides (L.) Thouars
- Showy Prairie Gentian - Eustoma Exaltatum (L.) Salisb. ex G. Don ssp. russellianum (Hook.) Kartesz
- Showy Pussytoes - Antennaria Pulcherrima (Hook.) Greene
- Showy Raillardella - Raillardella Pringlei Greene
- Showy Rattlebox - Crotalaria Spectabilis Roth
- Showy Sedge - Carex Spectabilis Dewey
- Showy Skullcap - Scutellaria Serrata Andrews
- Showy Spleenwort - Asplenium Formosum Willd.
- Showy Stickseed - Hackelia Hispida (A. Gray) I.M. Johnst.
- Showy Stickseed - Hackelia Hispida (A. Gray) I.M. Johnst. var. hispida
- Showy Stonecrop - Hylotelephium Spectabile (Boreau) H. Ohba
- Showy Sunflower - Helianthus Niveus (Benth.) Brandegee
- Showy Sunflower - Helianthus Niveus (Benth.) Brandegee ssp. canescens (A. Gray) Heiser
- Showy Tarweed - Madia Elegans D. Don ex Lindl. ssp. densifolia (Greene) D.D. Keck
- Showy Ticktrefoil - Desmodium Canadense (L.) DC.
- Showy Tonguefern - Elaphoglossum Decoratum (Kunze) T. Moore
- Showy Townsend Daisy - Townsendia Florifer (Hook.) A. Gray
- Showy Whitetop - Rhynchospora Nivea Boeckeler
- Showy Zephyrlily - Zephyranthes Pulchella J.G. Sm.
- Shredding Suncup - Camissonia Boothii (Douglas ex Lehm.) P.H. Raven ssp. condensata (Munz) P.H. Raven
- Shredding Suncup - Camissonia Boothii (Douglas ex Lehm.) P.H. Raven ssp. decorticans (Hook. & Arn.) P.
- Shreve Oak - Quercus Parvula Greene var. shrevei (C.H. Mull.) Nixon
- Shreve's Iris - Iris Virginica L. var. shrevei (Small) E.S. Anderson
- Shreve's Prairie Acacia - Acaciella Shrevei Britton & Rose
- Shrimpplant - Justicia Brandegeeana Wassh. & L.B. Sm.
- Shriver's Purple Fringed Orchid - Platanthera ×shriveri P.M. Br., (pro. sp.)
- Shrub Lespedeza - Lespedeza Bicolor Turcz.
- Shrub Panax - Pseudopanax Laetus (Kirk) Philipson
- Shrubby Alkaliaster - Machaeranthera Carnosa (A. Gray) G.L. Nesom
- Shrubby Alkaliaster - Machaeranthera Carnosa (A. Gray) G.L. Nesom var. carnosa
- Shrubby Alkaliaster - Machaeranthera Carnosa (A. Gray) G.L. Nesom var. intricata (A. Gray) G.L. Nesom
- Shrubby Bedstraw - Galium Multiflorum Kellogg
- Shrubby Blackberry - Rubus Fruticosus L. [excluded]
- Shrubby Blue Sage - Salvia Ballotiflora Benth.
- Shrubby Brickellbush - Brickellia Frutescens A. Gray
- Shrubby Bullseye - Gochnatia Hypoleuca (DC.) A. Gray
- Shrubby Cinquefoil - Dasiphora Fruticosa (L.) Rydb.
- Shrubby Cinquefoil - Dasiphora Fruticosa (L.) Rydb. ssp. floribunda (Pursh) Kartesz
- Shrubby Cinquefoil - Dasiphora Raf.
- Shrubby Copperleaf - Acalypha Phleoides Cav.
- Shrubby Daisybush - Osteospermum Fruticosum (L.) Norl.
- Shrubby Deervetch - Lotus Rigidus (Benth.) Greene
- Shrubby Dillenia - Dillenia Suffruticosa (Griffith ex Hook. f. & Thomson) Martelli
- Shrubby False Buttonweed - Spermacoce Verticillata L.
- Shrubby False Mallow - Malvastrum Bicuspidatum (S. Watson) Rose
- Shrubby Fivefingers - Sibbaldiopsis Tridentata (Aiton) Rydb.
- Shrubby Fuchsia - Fuchsia Paniculata Lindl.
- Shrubby Germander - Teucrium Fruticans L.
- Shrubby Honeysweet - Tidestromia Suffruticosa (Torr.) Standl.
- Shrubby Indian Mallow - Abutilon Abutiloides (Jacq.) Garcke ex Hochr.
- Shrubby Jerusalem Sage - Phlomis Fruticosa L.
- Shrubby Jointvetch - Aeschynomene Evenia C. Wright
- Shrubby Lespedeza - Lespedeza Frutescens (L.) Hornem.
- Shrubby Mayweed - Oncosiphon Suffruticosum (L.) Källersjö
- Shrubby Milkwort - Polygala Lindheimeri A. Gray
- Shrubby Milkwort - Polygala Lindheimeri A. Gray var. lindheimeri
- Shrubby Milkwort - Polygala Lindheimeri A. Gray var. parvifolia Wheelock
- Shrubby Nightshade - Solanum Robustum Wendl.
- Shrubby Pencilflower - Stylosanthes Fruticosa (Retz.) Alston
- Shrubby Primrose-willow - Ludwigia Suffruticosa Walter
- Shrubby Purslane - Portulaca Suffrutescens Engelm.
- Shrubby Restharrow - Ononis Fruticosa L.
- Shrubby Russian Thistle - Salsola Vermiculata L.
- Shrubby Sophora - Sophora Flavescens Aiton
- Shrubby St. Johnswort - Hypericum Prolificum L.
- Shrubby Starviolet - Hedyotis Fruticulosa (Volkens) Merr. var. fruticulosa
- Shrubby Thoroughwort - Koanophyllon Solidaginifolium (A. Gray) R.M. King & H. Rob.
- Shrubby Toothedthread - Odontonema Nitidum (Jacq.) Kuntze
- Shrubby Whitevein - Sanchezia Speciosa Leonard
- Shrubby Willowherb - Epilobium Suffruticosum Nutt.
- Shrubby Woodsorrel - Oxalis Frutescens L.
- Shrubby Woodsorrel - Oxalis Frutescens L. ssp. angustifolia (Kunth) Lourteig
- Shrubby Yellowcrest - Heimia Salicifolia (Kunth) Link
- Shrubby-spurge - Tetracoccus Engelm. ex Parry
- Shrubland Beggarticks - Bidens Sandvicensis Less.
- Shrubland Beggarticks - Bidens Sandvicensis Less. ssp. confusa Nagata & Ganders
- Shrubland Beggarticks - Bidens Sandvicensis Less. ssp. sandvicensis
- Shrubland Dubautia - Dubautia Linearis (Gaudich.) D.D. Keck
- Shrubland Dubautia - Dubautia Linearis (Gaudich.) D.D. Keck ssp. linearis
- Shrubland Dubautia - Dubautia Linearis (Gaudich.) D.D. Keck ssp. opposita (Sherff) G.D. Carr
- Shrubland Nehe - Lipochaeta Lobata (Gaudich.) DC.
- Shrubland Nehe - Lipochaeta Lobata (Gaudich.) DC. var. leptophylla O. Deg. & Sherff
- Shrubland Nehe - Lipochaeta Lobata (Gaudich.) DC. var. lobata
- Shultz's Blazingstar - Mentzelia Shultziorum Prigge
- Shumard Oak - Quercus Shumardii Buckley var. shumardii
- Shumard Oak - Quercus Shumardii Buckley var. stenocarpa Laughlin
- Shumard's Oak - Quercus Shumardii Buckley
- Shy Gilia - Gilia Inconspicua (Sm.) Sweet
- Shy Wallflower - Erysimum Inconspicuum (S. Watson) MacMill.
- Shy Wallflower - Erysimum Inconspicuum (S. Watson) MacMill. var. inconspicuum
- Shyleaf - Aeschynomene Americana L.
- Siala - Markhamia Lutea (Benth.) K. Schum.
- Siam Benzoin - Styrax Benzoides Craib
- Siam Benzoin - Styrax Tonkinensis (Pierre) Craib ex Hartwich
- Siam Hollygrape - Mahonia Siamensis Takeda
- Siamese Cassia - Senna Siamea (Lam.) Irwin & Barneby
- Sibara Runcinata (S. Watson) Rollins
- Sibara Runcinata (S. Watson) Rollins var. brachycarpa Rollins
- Sibaropsis - Sibaropsis S. Boyd & T.S. Ross
- Sibbaldia - Sibbaldia L.
- Sibbaldia Tridentata (Aiton) Paule & Soják
- Sibbaldiopsis - Sibbaldiopsis Rydb.
- Siberian Alder - Alnus Viridis (Chaix) DC. ssp. fruticosa (Rupr.) Nyman
- Siberian Bog Sedge - Kobresia Sibirica (Turcz. ex Ledeb.) Boeckeler
- Siberian Bugseed - Corispermum Pallasii Steven
- Siberian Candle Snuffer Moss - Encalypta Sibirica (Weinm.) Warnst.
- Siberian Catchfly - Silene Sibirica (L.) Persoon
- Siberian Crab Apple - Malus Baccata (L.) Borkh.
- Siberian Crab Apple - Malus Baccata (L.) Borkh. var. baccata
- Siberian Crab Apple - Malus Baccata (L.) Borkh. var. himalaica (Maxim.) C.K. Schneid.
- Siberian Crab Apple - Malus ×robusta (Carrière) Rehder
- Siberian Currant - Ribes Diacanthum Pall.
- Siberian Dock - Rumex Sibiricus Hultén
- Siberian Dotted Lichen - Bacidia Siberiensis (Willey) Zahlbr.
- Siberian Elm - Ulmus Pumila L.
- Siberian Geranium - Geranium Sibiricum L.
- Siberian Ginseng - Eleutherococcus Senticosus (Rupr. & Maxim.) Maxim.
- Siberian Hazelnut - Corylus Heterophylla Fisch. ex Trautv.
- Siberian Iris - Iris Sibirica L.
- Siberian Kale - Brassica Napus L. var. pabularia (DC.) Rchb.
- Siberian Larch - Larix Sibirica Ledeb.
- Siberian Larkspur - Delphinium Grandiflorum L.
- Siberian Melicgrass - Melica Altissima L.
- Siberian Mountain Ash - Sorbus Sambucifolia (Cham. & Schltdl.) M. Roem.
- Siberian Myurella Moss - Myurella Sibirica (Müll. Hal.) Reim.
- Siberian Oatgrass - Trisetum Sibiricum Rupr.
- Siberian Oatgrass - Trisetum Sibiricum Rupr. ssp. litorale Rupr. ex Rosh.
- Siberian Oatgrass - Trisetum Sibiricum Rupr. ssp. sibiricum
- Siberian Pea-tree - Caragana Boisii C.K. Schneid.
- Siberian Peashrub - Caragana Arborescens Lam.
- Siberian Phlox - Phlox Sibirica L.
- Siberian Pine - Pinus Sibirica Du Tour
- Siberian Polypody - Polypodium Sibiricum Sipl.
- Siberian Primrose - Primula Nutans Georgi
- Siberian Pseudoleskeella Moss - Pseudoleskeella Sibirica (Arnell) P. Wilson & Norris
- Siberian Pygmyweed - Crassula Sieberiana (Schult.) Druce
- Siberian Saltbush - Atriplex Sibirica L.
- Siberian Sea Rosemary - Argusia Sibirica (L.) Dandy
- Siberian Sea Thrift - Armeria Maritima (Mill.) Willd. ssp. sibirica (Turcz. ex Boiss.) Nyman
- Siberian Spikemoss - Selaginella Sibirica (Milde) Hieron.
- Siberian Springbeauty - Claytonia Sibirica L.
- Siberian Springbeauty - Claytonia Sibirica L. var. bulbifera A. Gray
- Siberian Springbeauty - Claytonia Sibirica L. var. sibirica
- Siberian Squill - Scilla Siberica Andrews
- Siberian Timmia Moss - Timmia Sibirica Lindb. & Arnell
- Siberian Wallflower - Erysimum ×marshallii (Henfr.) Bois
- Siberian Wheatgrass - Agropyron Fragile (Roth) P. Candargy
- Siberian Whitlowgrass - Draba Sibirica (Pall.) Thell.
- Siberian Whitlowgrass - Draba Sibirica (Pall.) Thell. ssp. arctica Böcher
- Siberian Wildrye - Elymus Sibiricus L.
- Siberian Wormwood - Artemisia Laciniata Willd.
- Siberian Yarrow - Achillea Sibirica Ledeb.
- Siberian-tea - Bergenia Crassifolia (L.) Fritsch
- Sicana - Sicana Naud.
- Sicilian Sumac - Rhus Coriaria L.
- Sickle Dichelyma Moss - Dichelyma Falcatum (Hedw.) Myr.
- Sickle Island Spleenwort - Diellia Falcata Brack.
- Sickle Kiaeria Moss - Kiaeria Falcata (Hedw.) I. Hagen
- Sickle Oligotrichum Moss - Oligotrichum Falcatum Steere
- Sickle Pigeonwings - Clitoria Falcata Lam.
- Sickle Saltbush - Atriplex Falcata (M.E. Jones) Standl.
- Sickle Senna - Senna Tora (L.) Roxb.
- Sickle Speenwort - Asplenium Polyodon G. Forst.
- Sickle Spurge - Euphorbia Falcata L.
- Sickle Tickseed - Coreopsis Falcata Boynt.
- Sicklefruit Fenugreek - Trigonella Foenum-graecum L.
- Sicklefruit Hypecoum - Hypecoum Imberbe Sm.
- Sicklefruit Jewelflower - Streptanthus Drepanoides Kruckeb. & Morrison
- Sicklegrass - Parapholis C.e. Hubbard
- Sicklekeel Lupine - Lupinus Albicaulis Douglas
- Sicklekeel Lupine - Lupinus Albicaulis Douglas var. albicaulis
- Sickleleaf Silkgrass - Pityopsis Falcata (Pursh) Nutt.
- Sickleleaf Tomentypnum Moss - Tomentypnum Falcifolium (Renauld ex Nichols) Tuom.
- Sicklepod - Arabis Canadensis L.
- Sicklepod Holdback - Hoffmannseggia Drepanocarpa A. Gray
- Sicklepod Rockcress - Arabis Sparsiflora Nutt.
- Sicklepod Rockcress - Arabis Sparsiflora Nutt. var. sparsiflora
- Sickletop Lousewort - Pedicularis Racemosa Douglas ex Benth.
- Sickletop Lousewort - Pedicularis Racemosa Douglas ex Benth. ssp. alba Pennell
- Sickletop Lousewort - Pedicularis Racemosa Douglas ex Benth. ssp. racemosa
- Sickleweed - Falcaria Vulgaris Bernh.
- Sicydium Lindheimeri (A. Gray) Greene var. tenuisectum A. Gray
- Sicyos Atollensis H. St. John
- Sicyos Caumii H. St. John
- Sicyos Collinus B.L. Rob. & Fernald [excluded]
- Sicyos Kaalaensis H. St. John
- Sicyos Kauaiensis H. St. John
- Sicyos Laciniatus L. var. genuinus Cogn.
- Sicyos Lamoureuxii H. St. John
- Sicyos Laysanensis H. St. John
- Sicyos Lobata Michx.
- Sicyos Microcarpus H. Mann
- Sicyos Nihoaensis H. St. John
- Sicyos Niihauensis H. St. John
- Sicyos Partitus H. St. John
- Sicyos Remyanus Cogn.
- Sicyos Trifoliatus L.
- Sicyosperma - Sicyosperma A. Gray
- Sida Acuminata DC.
- Sida Acuta Burm. f. ssp. carpinifolia (L. f.) Waalkes
- Sida Acuta Burm. f. var. carpinifolia (L. f.) K. Schum.
- Sida Alata S. Watson
- Sida Alba L.
- Sida Alcaeoides Michx.
- Sida Angustifolia auct. non Lam. p.p.
- Sida Carpinifolia L. f.
- Sida Ciliaris L. var. mexicana (Moric. ex Ser.) Shinners
- Sida Cordata auct. non (Burm. f.) Waalkes
- Sida Cristata L.
- Sida Cuneifolia A. Gray, non Roxb.
- Sida Eggersii Baker f.
- Sida Erecta Macfad.
- Sida Fallax Walp. var. kauaiensis Hochr.
- Sida Filicaulis Torr. & A. Gray
- Sida Filiformis Moric. ex Ser.
- Sida Filipes A. Gray
- Sida Grayana I. Clem.
- Sida Hederacea (Douglas ex Hook.) Torr. ex A. Gray
- Sida Helleri Rose ex A. Heller
- Sida Hispida Pursh
- Sida Holwayi Baker f. & Rose
- Sida Humilis Cav. var. veronicifolia Lam.
- Sida Humilis sensu Britton & P. Wilson
- Sida Inflexa Fernald
- Sida Javensis Cav. [excluded]
- Sida Javensis Cav. ssp. expilosa Waalkes
- Sida Ledyardii H. St. John
- Sida Lepidota A. Gray
- Sida Lepidota A. Gray var. sagittifolia A. Gray
- Sida Leprosa (Ortega) K. Schum.
- Sida Leprosa (Ortega) K. Schum. var. depauperata (A. Gray) I. Clem.
- Sida Leprosa (Ortega) K. Schum. var. hederacea (Douglas ex Hook.) K. Schum.
- Sida Leprosa (Ortega) K. Schum. var. sagittifolia (A. Gray) I. Clem.
- Sida Leptophylla Small
- Sida Meyeniana Walp.
- Sida Nelsonii H. St. John
- Sida Paniculata L.
- Sida Physaloides C. Presl
- Sida Physocalyx A. Gray
- Sida Procumbens Sw.
- Sida Pyramidata Cav.
- Sida Rhombifolia L. var. rhombifolia
- Sida Sagittifolia (A. Gray) Rydb.
- Sida Setifera C. Presl
- Sida Spinosa L. var. angustifolia auct. non (Lam.) Griseb. p.p.
- Sida Supina L'Hér.
- Sida Texana (Torr. & A. Gray) Small
- Sida Ulmifolia Mill.
- Sida Villosa Mill.
- Sidalcea Cusickii Piper ssp. purpurea C.L. Hitchc.
- Sidalcea Eximia Greene
- Sidalcea Hickmanii Greene var. parishii B.L. Rob.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. asprella (Greene) C.L. Hitchc.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. celata (Jeps.) C.L. Hitchc.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. elegans (Greene) C.L. Hitchc.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. nana (Jeps.) C.L. Hitchc.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. sparsifolia C.L. Hitchc.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. sparsifolia C.L. Hitchc. var. hirsu
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. sparsifolia C.L. Hitchc. var. spars
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. sparsifolia C.L. Hitchc. var. stell
- Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. sparsifolia C.L. Hitchc. var. uligi
- Sidalcea Malviflora (DC.) A. Gray ex Benth. var. californica (Nutt. ex Torr. & A. Gr
- Sidalcea Malviflora (DC.) A. Gray ex Benth. var. celata Jeps.
- Sidalcea Malviflora (DC.) A. Gray ex Benth. var. virgata (Howell) Dimling
- Sidalcea Neomexicana A. Gray var. covillei (Greene) Roush
- Sidalcea Neomexicana A. Gray var. crenulata (A. Nelson) C.L. Hitchc.
- Sidalcea Neomexicana A. Gray var. parviflora Greene
- Sidalcea Oregana (Nutt. ex Torr. & A. Gray) A. Gray var. cusickii (Piper) Roush
- Sidalcea Oregana (Nutt. ex Torr. & A. Gray) A. Gray var. spicata (Regel) Jeps.
- Sidalcea Reptans Greene var. nana Jeps.
- Sidalcea Rhizomata Jeps.
- Sidalcea Setosa C.L. Hitchc.
- Sidalcea Setosa C.L. Hitchc. ssp. querceta C.L. Hitchc.
- Sidalcea Spicata (Regel) Greene
- Sidalcea Spicata (Regel) Greene var. tonsa M. Peck
- Sidalcea Spicata (Regel) Greene var. valida (Greene) Wiggins
- Sidalcea Valida Greene
- Sidalcea Virgata Howell
- Sidastrum Acuminatum (DC.) Fryxell
- Sidebeak Pencilflower - Stylosanthes Biflora (L.) Britton, Sterns & Poggenb.
- Sidebells Penstemon - Penstemon Secundiflorus Benth.
- Sidebells Wintergreen - Orthilia Secunda (L.) House
- Sidecluster Milkweed - Asclepias Lanuginosa Nutt.
- Sideoats Grama - Bouteloua Curtipendula (Michx.) Torr.
- Sideoats Grama - Bouteloua Curtipendula (Michx.) Torr. var. caespitosa Gould & Kapadia
- Sideoats Grama - Bouteloua Curtipendula (Michx.) Torr. var. curtipendula
- Sideranthus Annuus Rydb.
- Sideranthus Aureus (A. Gray) Small
- Sideranthus Australis (Greene) Rydb.
- Sideranthus Cotula Small
- Sideranthus Glaberrimus Rydb.
- Sideranthus Gooddingii A. Nelson
- Sideranthus Gracilis (Nutt.) A. Nelson
- Sideranthus Grindelioides (Nutt.) Britton
- Sideranthus Laevis Wooton & Standl.
- Sideranthus Machaerantherus Small
- Sideranthus Megacephalus (Nash) Small
- Sideranthus Puberulus Rydb.
- Sideranthus Spinulosus (Pursh) Sweet ex Rydb.
- Sideranthus Spinulosus (Pursh) Sweet ex Rydb. var. glaberrimus (Rydb.) A. Nelson
- Sideranthus Turbinellus Rydb.
- Sideranthus Wootonii (Greene) Standl.
- Sideroxylon Rufohirtum Herring & W.S. Judd
- Sideroxylum Sapota Jacq.
- Sidesaddle Bristle Fern - Trichomanes Pusillum Sw.
- Sidopsis Hispida (Pursh) Rydb.
- Sieber's Crocus - Crocus Sieberi J. Gay
- Sieber's Filmy Fern - Hymenophyllum Sieberi (C. Presl) Bosch
- Siebold's Arrowwood - Viburnum Sieboldii Miq.
- Sieglingia Decumbens (L.) Bernh.
- Siella Erecta (Huds.) M. Pimen.
- Sierra Ancha Fleabane - Erigeron Anchana G.L. Nesom
- Sierra Baby Blue Eyes - Nemophila Spatulata Coville
- Sierra Bayberry - Myrica Hartwegii S. Watson
- Sierra Beardtongue - Penstemon Heterodoxus A. Gray
- Sierra Beardtongue - Penstemon Heterodoxus A. Gray var. cephalophorus (Greene) N.H. Holmgren
- Sierra Beardtongue - Penstemon Heterodoxus A. Gray var. heterodoxus
- Sierra Biscuitroot - Lomatium Torreyi (J.M. Coult. & Rose) J.M. Coult. & Rose
- Sierra Bladdernut - Staphylea Bolanderi A. Gray
- Sierra Blanca Cinquefoil - Potentilla Sierrae-blancae Wooton & Rydb.
- Sierra Blanca Least-daisy - Ionactis Elegans (Soreng & Spellenb.) G.L. Nesom
- Sierra Blazingstar - Mentzelia Crocea Kellogg
- Sierra Bleeding Heart - Dicentra Nevadensis Eastw.
- Sierra Bluecup - Githopsis Pulchella Vatke
- Sierra Bluecup - Githopsis Pulchella Vatke ssp. campestris Morin
- Sierra Bluecup - Githopsis Pulchella Vatke ssp. pulchella
- Sierra Bluecup - Githopsis Pulchella Vatke ssp. pulchella var. glabra (Jeps.) Morin
- Sierra Bluecup - Githopsis Pulchella Vatke ssp. pulchella var. pulchella
- Sierra Bluecup - Githopsis Pulchella Vatke ssp. serpentinicola Morin
- Sierra Bluegrass - Poa Sierrae J.T. Howell
- Sierra Bog Orchid - Platanthera Dilatata (Pursh) Lindl. ex Beck var. leucostachys (Lindl.) Luer
- Sierra Brodiaea - Brodiaea Minor (Benth.) S. Watson
- Sierra Brookfoam - Boykinia Intermedia (Piper) G.N. Jones
- Sierra Calicoflower - Downingia Montana Greene
- Sierra Checkerbloom - Sidalcea Reptans Greene
- Sierra Clarkia - Clarkia Virgata Greene
- Sierra Cliffbrake - Pellaea Brachyptera (T. Moore) Baker
- Sierra Columbine - Aquilegia Pubescens Coville
- Sierra Cryptantha - Cryptantha Nubigena (Greene) Payson
- Sierra Currant - Ribes Nevadense Kellogg
- Sierra Currant - Ribes Nevadense Kellogg var. glaucescens (Eastw.) A. Berger
- Sierra Currant - Ribes Nevadense Kellogg var. nevadense
- Sierra De Cayey Stopper - Eugenia Boqueronensis Britton
- Sierra De Luquillo Dwarf Polypody - Grammitis Hanekeana Proctor
- Sierra De Luquillo Filmy Fern - Hymenophyllum Decurrens (Jacq.) Sw.
- Sierra Draba - Draba Sierrae Sharsm.
- Sierra Erigeron - Erigeron Petrophilus Greene var. sierrensis G.L. Nesom
- Sierra False Bindweed - Calystegia Malacophylla (Greene) Munz
- Sierra False Bindweed - Calystegia Malacophylla (Greene) Munz ssp. malacophylla
- Sierra False Bindweed - Calystegia Malacophylla (Greene) Munz ssp. malacophylla var. berryi (Eastw.) Brummitt
- Sierra False Bindweed - Calystegia Malacophylla (Greene) Munz ssp. malacophylla var. malacophylla
- Sierra False Bindweed - Calystegia Malacophylla (Greene) Munz ssp. pedicellata (Jeps.) Munz
- Sierra False Coolwort - Bolandra Californica A. Gray
- Sierra False Mannagrass - Torreyochloa Californica (Beetle) Church
- Sierra False Needlegrass - Ptilagrostis Kingii (Bol.) Barkworth
- Sierra Fawnlily - Erythronium Multiscapoideum (Kellogg) A. Nelson & Kennedy
- Sierra Foothill Silverpuffs - Microseris Acuminata Greene
- Sierra Fringed Gentian - Gentianopsis Holopetala (A. Gray) Iltis
- Sierra Fumewort - Corydalis Caseana A. Gray
- Sierra Fumewort - Corydalis Caseana A. Gray ssp. brachycarpa (Rydb.) G.B. Ownbey
- Sierra Fumewort - Corydalis Caseana A. Gray ssp. caseana
- Sierra Fumewort - Corydalis Caseana A. Gray ssp. hastata (Rydb.) G.B. Ownbey
- Sierra Gooseberry - Ribes Roezlii Regel
- Sierra Gooseberry - Ribes Roezlii Regel var. amictum (Greene) Jeps.
- Sierra Gooseberry - Ribes Roezlii Regel var. roezlii
- Sierra Hare Sedge - Carex Leporinella Mack.
- Sierra Horkelia - Horkelia Congesta Douglas ex Hook.
- Sierra Horkelia - Horkelia Congesta Douglas ex Hook. ssp. congesta
- Sierra Horkelia - Horkelia Congesta Douglas ex Hook. ssp. nemorosa D.D. Keck
- Sierra Larkspur - Delphinium Glaucum S. Watson
- Sierra Laurel - Leucothoe Davisiae Torr. ex A. Gray
- Sierra Lessingia - Lessingia Leptoclada A. Gray
- Sierra Lewisia - Lewisia Glandulosa (Rydb.) Dempster
- Sierra Linanthus - Leptosiphon Pachyphyllus (R. Patt.) J.M. Porter & L.A. Johnson
- Sierra Lodgepole Pine - Pinus Contorta Douglas ex Loudon var. murrayana (Balf.) Engelm.
- Sierra Lupine - Lupinus Grayi (S. Watson) S. Watson
- Sierra Madre Larkspur - Delphinium Madrense S. Watson
- Sierra Madre Lobelia - Lobelia Laxiflora Kunth
- Sierra Madre Lobelia - Lobelia Laxiflora Kunth var. angustifolia A. DC.
- Sierra Madre St. Johnswort - Hypericum Parvulum Greene
- Sierra Manroot - Marah Horridus (Congd.) S.T. Dunn
- Sierra Mariposa Lily - Calochortus Minimus Ownbey
- Sierra Marsh Fern - Thelypteris Nevadensis (Baker) Clute ex Morton
- Sierra Milkvetch - Astragalus Lentiginosus Douglas ex Hook. var. sierrae M.E. Jones
- Sierra Milkwort - Polygala Cornuta Kellogg
- Sierra Milkwort - Polygala Cornuta Kellogg var. cornuta
- Sierra Milkwort - Polygala Cornuta Kellogg var. fishiae (Parry) Jeps.
- Sierra Mint - Pycnanthemum Californicum Torr. ex Durand
- Sierra Mock Stonecrop - Sedella Pumila (Benth.) Britton & Rose
- Sierra Monardella - Monardella Candicans Benth.
- Sierra Mousetail - Ivesia Santolinoides A. Gray
- Sierra Nakedwood - Colubrina Greggii S. Watson
- Sierra Needlegrass - Achnatherum Latiglume (Swallen) Barkworth
- Sierra Nevada Linanthus - Leptosiphon Oblanceolatus (Brand) J.M. Porter & L.A. Johnson
- Sierra Pea - Lathyrus Nevadensis S. Watson
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. cusickii (S. Watson) C.L. Hitchc.
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. lanceolatus (Howell) C.L. Hitchc.
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. lanceolatus (Howell) C.L. Hitchc. var. nuttallii
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. lanceolatus (Howell) C.L. Hitchc. var. parkeri (H
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. lanceolatus (Howell) C.L. Hitchc. var. pilosellus
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. lanceolatus (Howell) C.L. Hitchc. var. puniceus C
- Sierra Pea - Lathyrus Nevadensis S. Watson ssp. nevadensis
- Sierra Primrose - Primula Suffrutescens A. Gray
- Sierra Pussytoes - Antennaria Pulchella Greene
- Sierra Ragwort - Senecio Scorzonella Greene
- Sierra Rush - Juncus Nevadensis S. Watson
- Sierra Rush - Juncus Nevadensis S. Watson var. badius (Suksd.) C.L. Hitchc.
- Sierra Rush - Juncus Nevadensis S. Watson var. inventus (L.F. Hend.) C.L. Hitchc.
- Sierra Rush - Juncus Nevadensis S. Watson var. nevadensis
- Sierra Saxifrage - Saxifraga Aprica Greene
- Sierra Sedge - Carex Nervina L.H. Bailey
- Sierra Shootingstar - Dodecatheon Jeffreyi Van Houtte
- Sierra Shootingstar - Dodecatheon Jeffreyi Van Houtte ssp. jeffreyi
- Sierra Shootingstar - Dodecatheon Jeffreyi Van Houtte ssp. pygmaeum (H.M. Hall) H.J. Thomp.
- Sierra Shootingstar - Dodecatheon Subalpinum Eastw.
- Sierra Skullcap - Scutellaria Bolanderi A. Gray
- Sierra Skullcap - Scutellaria Bolanderi A. Gray ssp. austromontana Epling
- Sierra Skullcap - Scutellaria Bolanderi A. Gray ssp. bolanderi
- Sierra Slender Sedge - Carex Teneriformis Mack.
- Sierra Snapdragon - Sairocarpus Multiflorus (Pennell) D.A. Sutton
- Sierra Springbeauty - Claytonia Nevadensis S. Watson
- Sierra Stickseed - Hackelia Nervosa (Kellogg) I.M. Johnst.
- Sierra Stonecrop - Sedum Obtusatum A. Gray
- Sierra Stonecrop - Sedum Obtusatum A. Gray ssp. boreale R.T. Clausen
- Sierra Stonecrop - Sedum Obtusatum A. Gray ssp. obtusatum
- Sierra Stonecrop - Sedum Obtusatum A. Gray ssp. retusum (Rose) R.T. Clausen
- Sierra Suncup - Camissonia Sierrae P.H. Raven
- Sierra Suncup - Camissonia Sierrae P.H. Raven ssp. sierrae
- Sierra Tansymustard - Descurainia Californica (A. Gray) O.E. Schulz
- Sierra Threadplant - Nemacladus Interior (Munz) G.T. Robbins
- Sierra Tidytips - Layia Pentachaeta A. Gray
- Sierra Tidytips - Layia Pentachaeta A. Gray ssp. albida D.D. Keck
- Sierra Tidytips - Layia Pentachaeta A. Gray ssp. pentachaeta
- Sierra Tiger Lily - Lilium Parvum Kellogg
- Sierra Triteleia - Triteleia Montana Hoover
- Sierra Valley Evening Primrose - Camissonia Tanacetifolia (Torr. & A. Gray) P.H. Raven ssp. quadriperforata P.H. Raven
- Sierra Valley Mousetail - Ivesia Aperta (J.T. Howell) Munz
- Sierra Valley Mousetail - Ivesia Aperta (J.T. Howell) Munz var. aperta
- Sierra Valley Mousetail - Ivesia Aperta (J.T. Howell) Munz var. canina Ertter
- Sierra White Fir - Abies Lowiana (Gordon & Glend.) A. Murray bis
- Sierra Wildrye - Elymus Sierrus Gould
- Sierra Willow - Salix Orestera C.K. Schneid.
- Sierra Woodrush - Luzula Orestera Sharsm.
- Sierra Woolly Indian Paintbrush - Castilleja Lanata A. Gray
- Sierra Woolly Indian Paintbrush - Castilleja Lanata A. Gray ssp. lanata
- Sierran Palm - Prestoea Acuminata (Willd.) H.E. Moore
- Sierran Palm - Prestoea Acuminata (Willd.) H.E. Moore var. montana (Graham) A. Hend. & G. Galeano
- Sieva Bean - Phaseolus Lunatus L.
- Sieversia Campanulata (Greene) Rydb.
- Sieversia Canescens (Greene) Rydb.
- Sieversia Ciliata (Pursh) G. Don
- Sieversia Gracilipes (Piper) Greene
- Sieversia Peckii (Pursh) Rydb.
- Sieversia Pentapetala (L.) Greene
- Sieversia Radiata (Michx.) Greene
- Sieversia Triflora (Pursh) R. Br.
- Sieversia ×macrantha Kearney
- Sigesbeckia Jorullensis Kunth [excluded]
- Sigesbeckia Laciniata Poir.
- Sigmoid Threadplant - Nemacladus Sigmoideus G.T. Robbins
- Signalgrass - Brachiaria (trin.) Griseb.
- Signalgrass - Urochloa P. Beauv.
- Sigridea Californica (Tuck.) Tehler
- Sigridea Tehler
- Silene Acaulis (L.) Jacq. ssp. arctica Á. Löve & D. Löve
- Silene Acaulis (L.) Jacq. ssp. subacaulescens (F.N. Williams) Hultén
- Silene Alba (Mill.) Krause
- Silene Andersonii Clokey
- Silene Anglica L.
- Silene Antirrhina L. var. confinis Fernald
- Silene Antirrhina L. var. depauperata Rydb.
- Silene Antirrhina L. var. divaricata B.L. Rob.
- Silene Antirrhina L. var. laevigata Engelm. & A. Gray
- Silene Antirrhina L. var. subglaber Engelm. & A. Gray
- Silene Antirrhina L. var. vaccarifolia Rydb.
- Silene Apetala Willd. [excluded]
- Silene Atropurpurea (Griseb.) Greuter & Burdet
- Silene Attenuata (Farr) Bocquet
- Silene Baldwinii Nutt.
- Silene Campanulata S. Watson var. greenei S. Watson
- Silene Campanulata S. Watson var. orbiculata B.L. Rob.
- Silene Caroliniana Walter var. pensylvanica (Michx.) Fernald
- Silene Caroliniana Walter var. wherryi (Small) Fernald
- Silene Coronaria (L.) Clairville
- Silene Cucubalus Wibel
- Silene Dorrii Kellogg
- Silene Douglasii Hook. var. macounii (S. Watson) B.L. Rob.
- Silene Douglasii Hook. var. monantha (S. Watson) B.L. Rob.
- Silene Douglasii Hook. var. villosa C.L. Hitchc. & Maguire
- Silene Flos-cuculi (L.) Greuter & Burdet
- Silene Flos-jovis (L.) Greuter & Burdet
- Silene Furcata Raf.
- Silene Glauca Lag., nom. illeg.
- Silene Grandis Eastw.
- Silene Hallii S. Watson
- Silene Hawaiiensis Sherff var. kaupoana (O. Deg. & Sherff) O. Deg. & Sherff
- Silene Hitchguirei Bocquet
- Silene Inaperta L.
- Silene Inflata Sm.
- Silene Ingramii Tidestr. & Dayton
- Silene Insectivora L.F. Hend.
- Silene Involucrata (Cham. & Schltdl.) Bocquet ssp. tenella (Tolm.) Bocquet
- Silene Laciniata Cav. var. greggii (A. Gray) S. Watson
- Silene Lanceolata A. Gray var. angustifolia Hillebr.
- Silene Lanceolata A. Gray var. forbesii Sherff
- Silene Lanceolata A. Gray var. hillebrandii Sherff
- Silene Latifolia (Mill.) Britten & Rendle, non Poir.
- Silene Lyallii S. Watson
- Silene Macounii S. Watson
- Silene Maritima With.
- Silene Menziesii Hook. var. williamsii (Britton) B. Boivin
- Silene Montana S. Watson ssp. bernardina (S. Watson) C.L. Hitchc. & Maguire
- Silene Montana S. Watson var. rigidula B.L. Rob.
- Silene Montana S. Watson var. sierrae C.L. Hitchc. & Maguire
- Silene Montana S. Watson var. viscida L.F. Hend.
- Silene Montana S. Watson, non Arrond.
- Silene Obovata A.E. Porsild
- Silene Occidentalis S. Watson var. nancta Jeps.
- Silene Oraria M. Peck
- Silene Pacifica Eastw.
- Silene Pectinata S. Watson
- Silene Pensylvanica Michx.
- Silene Platyota S. Watson
- Silene Pratensis (Raf.) Gren. & Godr.
- Silene Pulverulenta M. Peck
- Silene Pumilio (L.) Wulfen
- Silene Purpurata Greene
- Silene Repens Patrin ex Pers. var. australis (C.L. Hitchc. & Maguire) C.L. Hit
- Silene Repens Patrin ex Pers. var. costata (F.N. Williams) B. Boivin
- Silene Rupestris L.
- Silene Scouleri Hook. ssp. grandis (Eastw.) C.L. Hitchc. & Maguire
- Silene Scouleri Hook. var. macounii (S. Watson) B. Boivin
- Silene Secundiflora Otth
- Silene Serpentinicola T.W. Nelson & J.P. Nelson
- Silene Shockleyi S. Watson
- Silene Stellata (L.) W.T. Aiton var. scabrella Palmer & Steyerm.
- Silene Tetonensis A. Nelson
- Silene Uralensis (Rupr.) Bocquet ssp. apetala (L.) Bocquet
- Silene Uralensis (Rupr.) Bocquet ssp. porsildii Bocquet
- Silene Virginica L. var. hallensis A.L. Pickens & M.C. Pickens
- Silene Viscaria (L.) Jessen
- Silene Vulgaris (Moench) Garcke ssp. maritima (With.) Á. Löve & D. Löve
- Silene Wahlbergella Chowdhuri
- Silene Wahlbergella Chowdhuri ssp. arctica (Fr.) Hultén
- Silene Wahlbergella Chowdhuri ssp. attenuata (Farr) Hultén
- Silene Wahlbergella Chowdhuri ssp. montana (S. Watson) Hultén
- Silene Watsonii B.L. Rob.
- Silene Wherryi Small
- Silene Williamsii Britton
- Silene ×intermedia (Schur) Philip, nom. illeg., non Silene ×intermedia (Lange) Bocq
- Siler Fishhook Cactus - Sclerocactus Sileri (L.D. Benson) K.D. Heil & J.M. Porter
- Siler Pincushion Cactus - Pediocactus Sileri (Engelm. ex J.M. Coult.) L.D. Benson
- Siler's Penstemon - Penstemon Linarioides A. Gray ssp. sileri (A. Gray) D.D. Keck
- Siler's Tuberose - Manfreda Sileri Verh-Will.
- Silk Bay - Persea Humilis Nash
- Silk Cottontree - Cochlospermum Vitifolium (Willd.) Willd. ex Spreng.
- Silk-cotton Tree - Cochlospermum Religiosum (L.) Alston
- Silk-floss Tree - Chorisia Kunth
- Silk-floss Tree - Chorisia Speciosa A. St.-Hil.
- Silkcotton Purslane - Portulaca Halimoides L.
- Silken Homalothecium Moss - Homalothecium Sericeum (Hedw.) Schimp.
- Silkgrass - Pityopsis Nutt.
- Silkleaf - Lagascea Mollis Cav.
- Silkoak - Grevillea Robusta A. Cunn. ex R. Br.
- Silkreed - Neyraudia Reynaudiana (Kunth) Keng ex Hitchc.
- Silkrubber - Funtumia Elastica (Preuss) Stapf
- Silktassel - Garrya Douglas ex Lindl.
- Silktree - Albizia Julibrissin Durazz.
- Silkvine - Periploca Graeca L.
- Silky Balsamroot - Balsamorhiza Sericea W.A. Weber
- Silky Beach Pea - Lathyrus Littoralis (Nutt.) Endl.
- Silky Bluestem - Dichanthium Sericeum (R. Br.) A. Camus
- Silky Camellia - Stewartia Malacodendron L.
- Silky Celtis - Celtis Paniculata (Endl.) Planch.
- Silky Cinquefoil - Potentilla Pseudosericea Rydb.
- Silky Cryptantha - Cryptantha Sericea (A. Gray) Payson
- Silky Deerweed - Lotus Procumbens (Greene) Greene
- Silky Deerweed - Lotus Procumbens (Greene) Greene var. procumbens
- Silky Dogwood - Cornus Amomum Mill.
- Silky Dogwood - Cornus Obliqua Raf.
- Silky Horkelia - Horkelia Sericata S. Watson
- Silky Jackbean - Canavalia Sericea A. Gray
- Silky Kangaroo Grass - Themeda Villosa (Poir.) A. Camus
- Silky Lupine - Lupinus Sericeus Pursh
- Silky Lupine - Lupinus Sericeus Pursh ssp. huffmanii (C.P. Sm.) Fleak & D. Dunn
- Silky Lupine - Lupinus Sericeus Pursh ssp. marianus (Rydb.) Fleak & D. Dunn
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus var. egglestonianus C.P. Sm.
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus var. flexuosus (Lindl. ex J. Agardh) C.P. Sm
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus var. maximus C.P. Sm. ex Fleak & D. Dunn
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus var. sericeus
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus var. thompsonianus C.P. Sm.
- Silky Lupine - Lupinus Sericeus Pursh ssp. sericeus var. wallowensis C.P. Sm.
- Silky Milkvetch - Astragalus Sericoleucus A. Gray
- Silky Morning-glory - Ipomoea Pubescens Lam.
- Silky Mousetail - Ivesia Pickeringii Torr. ex A. Gray
- Silky Myrtle - Decaspermum Parviflorum (Lam.) A.J. Scott
- Silky Phacelia - Phacelia Sericea (Graham) A. Gray
- Silky Phacelia - Phacelia Sericea (Graham) A. Gray ssp. ciliosa (Rydb.) G.W. Gillett
- Silky Phacelia - Phacelia Sericea (Graham) A. Gray ssp. sericea
- Silky Prairie Clover - Dalea Villosa (Nutt.) Spreng.
- Silky Prairie Clover - Dalea Villosa (Nutt.) Spreng. var. grisea (Torr. & A. Gray) Barneby
- Silky Prairie Clover - Dalea Villosa (Nutt.) Spreng. var. villosa
- Silky Raillardella - Raillardella Argentea (A. Gray) A. Gray
- Silky Silverbush - Argythamnia Argyraea Cory
- Silky Sophora - Sophora Nuttalliana B.L. Turner
- Silky Thatching Grass - Hyparrhenia Dregeana (Nees) Stent
- Silky Willow - Salix Sericea Marshall
- Silky-leaf Osier - Salix ×smithiana Willd. (pro sp.)
- Silkybent - Apera Adans.
- Silkyleaf Cinquefoil - Potentilla Ambigens Greene
- Silkyscale - Anthaenantia P. Beauv.
- Silphium Angustum (A. Gray) Small
- Silphium Asperrimum Hook.
- Silphium Asteriscus L. var. dentatum (Elliott) Chapm.
- Silphium Asteriscus L. var. scabrum Nutt.
- Silphium Atropurpureum Retz. ex Willd.
- Silphium Chickamaugense Canby
- Silphium Compositum Michx. ssp. ovatifolium (Torr. & A. Gray) Sweeny & T.R. Fisher
- Silphium Compositum Michx. ssp. reniforme (Raf. ex Nutt.) Sweeny & T.R. Fisher
- Silphium Compositum Michx. ssp. venosum (Small) Sweeny & T.R. Fisher
- Silphium Confertifolium Small
- Silphium Connatum L.
- Silphium Dentatum Elliott
- Silphium Dentatum Elliott var. angustatum (A. Gray) L.M. Perry
- Silphium Dentatum Elliott var. gatesii (C. Mohr) H.E. Ahles
- Silphium Elliottii Small
- Silphium Gatesii C. Mohr
- Silphium Glabrum Eggert ex Small
- Silphium Incisum Greene
- Silphium Laevigatum Elliott, non Pursh
- Silphium Laevigatum Pursh
- Silphium Lapsuum Small
- Silphium Nodum Small
- Silphium Orae Small
- Silphium Ovatifolium (Torr. & A. Gray) Small
- Silphium Perfoliatum L. ssp. connatum (L.) Cruden
- Silphium Reniforme Raf. ex Nutt.
- Silphium Rumicifolium Small
- Silphium Scabrum Moench, non Walter
- Silphium Simpsonii Greene var. wrightii L.M. Perry
- Silphium Speciosum Nutt.
- Silphium Terebinthinaceum Elliott, non Jacq.
- Silphium Terebinthinaceum Jacq. var. pinnatifidum (Elliott) A. Gray
- Silphium Trilobatum L.
- Silphium Venosum Small
- Siltbush - Zuckia Brandegeei (A. Gray) S.L. Welsh & Stutz ex S.L. Welsh
- Siltbush - Zuckia Brandegeei (A. Gray) S.L. Welsh & Stutz ex S.L. Welsh var. brandegeei
- Silver Banksia - Banksia Marginata Cav.
- Silver Beardgrass - Bothriochloa Laguroides (DC.) Herter
- Silver Beardgrass - Bothriochloa Laguroides (DC.) Herter ssp. laguroides
- Silver Beardgrass - Bothriochloa Laguroides (DC.) Herter ssp. torreyana (Steud.) Allred & Gould
- Silver Bird's-foot Trefoil - Lotus Argophyllus (A. Gray) Greene
- Silver Bird's-foot Trefoil - Lotus Argophyllus (A. Gray) Greene var. argenteus Dunkle
- Silver Bird's-foot Trefoil - Lotus Argophyllus (A. Gray) Greene var. argophyllus
- Silver Bladderpod - Lesquerella Argyraea (A. Gray) S. Watson
- Silver Bluestem - Bothriochloa Saccharoides (Sw.) Rydb.
- Silver Buffaloberry - Shepherdia Argentea (Pursh) Nutt.
- Silver Bur Ragweed - Ambrosia Chamissonis (Less.) Greene
- Silver Chickensage - Sphaeromeria Argentea Nutt.
- Silver Cinquefoil - Potentilla Argentea L.
- Silver Cinquefoil - Potentilla Argentea L. var. argentea
- Silver Cinquefoil - Potentilla Argentea L. var. pseudocalabra T. Wolf
- Silver Cock's Comb - Celosia Argentea L.
- Silver Creek Blackberry - Rubus Parcifrondifer L.H. Bailey
- Silver Draba - Draba Argyrea Rydb.
- Silver Dwarf Morning-glory - Evolvulus Sericeus Sw.
- Silver Dwarf Morning-glory - Evolvulus Sericeus Sw. var. glaberrimus B.L. Rob.
- Silver Dwarf Morning-glory - Evolvulus Sericeus Sw. var. sericeus
- Silver False Spleenwort - Deparia Acrostichoides (Sw.) M. Kato
- Silver Fir - Abies Alba Mill.
- Silver Fleabane - Erigeron Argentatus A. Gray
- Silver Hairgrass - Aira Caryophyllea L.
- Silver Hairgrass - Aira Caryophyllea L. var. caryophyllea
- Silver Hairgrass - Aira Caryophyllea L. var. cupaniana (Guss.) Fiori
- Silver July Croton - Croton Argenteus L.
- Silver Linden - Tilia Tomentosa Moench
- Silver Lupine - Lupinus Albifrons Benth.
- Silver Lupine - Lupinus Albifrons Benth. var. albifrons
- Silver Lupine - Lupinus Albifrons Benth. var. collinus Greene
- Silver Lupine - Lupinus Albifrons Benth. var. eminens (Greene) C.P. Sm.
- Silver Lupine - Lupinus Albifrons Benth. var. flumineus C.P. Sm.
- Silver Maple - Acer Saccharinum L.
- Silver Mock Orange - Philadelphus Argenteus Rydb.
- Silver Mountain Mahogany - Cercocarpus Montanus Raf. var. argenteus (Rydb.) F.L. Martin
- Silver Palm - Coccothrinax Sarg.
- Silver Plumegrass - Saccharum Alopecuroides (L.) Nutt.
- Silver Ponysfoot - Dichondra Argentea Humb. & Bonpl. ex Willd.
- Silver Prairie Clover - Dalea Bicolor Humb. & Bonpl. ex Willd.
- Silver Prairie Clover - Dalea Bicolor Humb. & Bonpl. ex Willd. var. argyrea (A. Gray) Barneby
- Silver Pussytoes - Antennaria Argentea Benth.
- Silver Pygmycudweed - Evax Candida (Torr. & A. Gray) A. Gray
- Silver Rockcress - Arabis Puberula Nutt.
- Silver Sage - Salvia Argentea L.
- Silver Sagebrush - Artemisia Cana Pursh
- Silver Sagebrush - Artemisia Cana Pursh ssp. bolanderi (A. Gray) G.H. Ward
- Silver Sagebrush - Artemisia Cana Pursh ssp. cana
- Silver Sagebrush - Artemisia Cana Pursh ssp. viscidula (Osterh.) Beetle
- Silver Saltbush - Atriplex Bunburyana F. Muell.
- Silver Saltbush - Atriplex Rhagodioides F. Muell.
- Silver Senna - Senna Artemisioides (Gaudich. ex DC.) Randell
- Silver Tussock - Poa Cita Edgar
- Silver Twinpod - Physaria Scrotiformis O'Kane
- Silver Vine - Actinidia Polygama (Siebold & Zucc.) Maxim.
- Silver Wattle - Acacia Dealbata Link
- Silver's Milkvetch - Astragalus Subcinereus A. Gray
- Silver-dollar Eucalyptus - Eucalyptus Cordata Labill.
- Silver-leaf Ironbark - Eucalyptus Melanophloia F. Muell.
- Silver-stem Wattle - Acacia Parvipinnula Tindale
- Silver-top Gimlet - Eucalyptus Campaspe S. Moore
- Silverback Fern - Pentagramma Triangularis (Kaulf.) Yatsk., Windham & E. Wollenw. ssp. viscosa (D.C. Eaton)
- Silverback - Luina Benth.
- Silverbell - Halesia Ellis ex L.
- Silverberry - Elaeagnus Commutata Bernh. ex Rydb.
- Silverbush - Argythamnia P. Br.
- Silvercrown - Cacaliopsis Nardosmia (A. Gray) A. Gray
- Silvercup Mock Orange - Philadelphus Argyrocalyx Wooton
- Silvergrass - Miscanthus Andersson
- Silvergrass - Miscanthus Capensis (Nees) Andersson
- Silvergrass - Miscanthus Transmorrisonensis Hayata
- Silvergreen Bryum Moss - Bryum Argenteum Hedw.
- Silverhair Mousetail - Ivesia Argyrocoma (Rydb.) Rydb.
- Silverhair Pineapplegrass - Astelia Argyrocoma A. Heller ex Skottsb.
- Silverhead - Blutaparon Vermiculare (L.) Mears
- Silverleaf Cotoneaster - Cotoneaster Pannosus Franch.
- Silverleaf Hydrangea - Hydrangea Radiata Walter
- Silverleaf Indian Breadroot - Pediomelum Argophyllum (Pursh) J. Grimes
- Silverleaf Milkvetch - Astragalus Argophyllus Nutt.
- Silverleaf Milkvetch - Astragalus Argophyllus Nutt. var. argophyllus
- Silverleaf Milkvetch - Astragalus Argophyllus Nutt. var. martinii M.E. Jones
- Silverleaf Milkvetch - Astragalus Argophyllus Nutt. var. panguicensis (M.E. Jones) M.E. Jones
- Silverleaf Milkvetch - Astragalus Argophyllus Nutt. var. stocksii (S.L. Welsh) Barneby ex Isely
- Silverleaf Mountain Gum - Eucalyptus Pulverulenta Sims
- Silverleaf Nightshade - Solanum Elaeagnifolium Cav.
- Silverleaf Nutmeg - Myristica Hypargyraea A. Gray
- Silverleaf Oak - Quercus Hypoleucoides A. Camus
- Silverleaf Phacelia - Phacelia Hastata Douglas ex Lehm.
- Silverleaf Phacelia - Phacelia Hastata Douglas ex Lehm. var. hastata
- Silverleaf Ponysfoot - Dichondra Sericea Sw.
- Silverleaf Sunflower - Helianthus Argophyllus Torr. & A. Gray
- Silverleaf Sunray - Enceliopsis Argophylla (D.C. Eaton) A. Nelson
- Silverleafed Princess Flower - Tibouchina Heteromalla Cogn.
- Silverling - Baccharis Glomeruliflora Pers.
- Silverpuff - Chaptalia Texana Greene
- Silverpuffs - Microseris D. Don
- Silverscale Saltbush - Atriplex Argentea Nutt.
- Silverscale Saltbush - Atriplex Argentea Nutt. ssp. argentea
- Silverscale Saltbush - Atriplex Argentea Nutt. ssp. argentea var. argentea
- Silverscale Saltbush - Atriplex Argentea Nutt. ssp. expansa (S. Watson) H.M. Hall & Clem.
- Silversheath Knotweed - Polygonum Argyrocoleon Steud. ex Kunze
- Silverskin Lichen - Dermatocarpon Eschw.
- Silverskin Lichen - Dermatocarpon Luridum (With.) J.R. Laundon
- Silverskin Lichen - Dermatocarpon Miniatum (L.) W. Mann
- Silverskin Lichen - Dermatocarpon Rivulorum (Arnold) Dalla Torre & Sarnth.
- Silverskin Lichen - Dermatocarpon Saxicola (de Lesd.) ?, ined.?
- Silverskin Lichen - Dermatocarpon Vellereum Zschacke
- Silversword - Argyroxiphium Dc.
- Silversword - Argyroxiphium ×kai (Forbes) D.D. Keck
- Silvertop - Glehnia F. Schmidt ex Miq.
- Silvertop Stringybark - Eucalyptus Laevopinea R.T. Baker
- Silvertop-ash - Eucalyptus Sieberi L.A.S. Johnson
- Silverweed - Argentina Hill
- Silverweed Cinquefoil - Argentina Anserina (L.) Rydb.
- Silverweed - Potentilla Elegans Cham. & Schltdl.
- Silvery Everlasting - Gamochaeta Argyrinea G.L. Nesom
- Silvery Lupine - Lupinus Argenteus Pursh
- Silvery Lupine - Lupinus Argenteus Pursh ssp. argenteus
- Silvery Lupine - Lupinus Argenteus Pursh ssp. argenteus var. argenteus
- Silvery Lupine - Lupinus Argenteus Pursh ssp. argenteus var. laxiflorus (Douglas ex Lindl.) Dorn
- Silvery Lupine - Lupinus Argenteus Pursh ssp. ingratus (Greene) Harmon
- Silvery Lupine - Lupinus Argenteus Pursh ssp. moabensis D. Dunn & Harmon
- Silvery Lupine - Lupinus Argenteus Pursh ssp. rubricaulis (Greene) Hess & D. Dunn
- Silvery Lupine - Lupinus Argenteus Pursh ssp. spathulatus (Rydb.) Hess & D. Dunn
- Silvery Nailwort - Paronychia Argyrocoma (Michx.) Nutt.
- Silvery Primrose - Primula Incana M.E. Jones
- Silvery Sedge - Carex Canescens L.
- Silvery Sedge - Carex Canescens L. ssp. canescens
- Silvery Sedge - Carex Canescens L. ssp. disjuncta (Fernald) Toivonen
- Silveus' Dropseed - Sporobolus Silveanus Swallen
- Silveus' Grass - Trichoneura Andersson
- Silveus' Grass - Trichoneura Elegans Swallen
- Silveus' Lovegrass - Eragrostis Silveana Swallen
- Silybum Eburneum Coss. & Durieu
- Simarouba - Simarouba Aubl.
- Simil Onion - Allium Simillimum L.F. Hend.
- Simmonds' Aster - Symphyotrichum Simmondsii (Small) G.L. Nesom
- Simmondsia Californica Nutt.
- Simon Bamboo - Pleioblastus Simonii (Carrière) Nakai
- Simon Poplar - Populus Simonii Carrière [excluded]
- Simons' Cotoneaster - Cotoneaster Simonsii Baker
- Simple Bog Sedge - Kobresia Simpliciuscula (Wahlenb.) Mack.
- Simple Campion - Silene Scouleri Hook.
- Simple Campion - Silene Scouleri Hook. ssp. hallii (S. Watson) C.L. Hitchc. & Maguire
- Simple Campion - Silene Scouleri Hook. ssp. pringlei (S. Watson) C.L. Hitchc. & Maguire
- Simple Campion - Silene Scouleri Hook. ssp. pringlei (S. Watson) C.L. Hitchc. & Maguire var. conc
- Simple Campion - Silene Scouleri Hook. ssp. pringlei (S. Watson) C.L. Hitchc. & Maguire var. egla
- Simple Campion - Silene Scouleri Hook. ssp. pringlei (S. Watson) C.L. Hitchc. & Maguire var. gris
- Simple Campion - Silene Scouleri Hook. ssp. pringlei (S. Watson) C.L. Hitchc. & Maguire var. lept
- Simple Campion - Silene Scouleri Hook. ssp. pringlei (S. Watson) C.L. Hitchc. & Maguire var. prin
- Simple Campion - Silene Scouleri Hook. ssp. scouleri
- Simple Campion - Silene Scouleri Hook. ssp. scouleri var. pacifica (Eastw.) C.L. Hitchc.
- Simple Campion - Silene Scouleri Hook. ssp. scouleri var. scouleri
- Simple-stem Everlasting - Gamochaeta Simplicicaulis (Willd. ex Spreng.) Cabrera
- Simplebeak Ironwort - Sideritis Romana L.
- Simpleleaf Bushweed - Flueggea Acidoton (L.) G.L. Webster
- Simpleleaf Chastetree - Vitex Trifolia L.
- Simpleleaf Chastetree - Vitex Trifolia L. var. bicolor (Willd.) Moldenke
- Simpleleaf Chastetree - Vitex Trifolia L. var. subtrisecta (Kuntze) Moldenke
- Simpleleaf Chastetree - Vitex Trifolia L. var. trifolia
- Simpleleaf Ticktrefoil - Desmodium Psilophyllum Schltdl.
- Simpler Hollyfern - Arachniodes Simplicior (Makino) Ohwi
- Simplestem Bur-reed - Sparganium Erectum L.
- Simplestem Bur-reed - Sparganium Erectum L. ssp. stoloniferum (Graebn.) H. Hara
- Simpson's Applecactus - Harrisia Simpsonii Small
- Simpson's Buckwheat - Eriogonum Microthecum Nutt. var. simpsonii (Benth.) Reveal
- Simpson's Cupgrass - Eriochloa Michauxii (Poir.) Hitchc. var. simpsonii Hitchc.
- Simpson's Grasspink - Calopogon Tuberosus (L.) Britton, Sterns & Poggenb. var. simpsonii (Small) Magrath
- Simpson's Primrose-willow - Ludwigia Simpsonii Chapm.
- Simpson's Rosinweed - Silphium Simpsonii Greene
- Simpsonia Microcarpa (Sarg.) O.F. Cook
- Simsia Exaristata A. Gray
- Simsia Exaristata A. Gray var. perplexa S.F. Blake
- Simsia Frutescens A. Gray
- Simsia Scaposa A. Gray
- Sinai Jerusalem Sage - Phlomis Aurea Decne.
- Sinapis Alba L. ssp. dissecta (Lag.) Bonnier
- Sinapis Arvensis L. var. orientalis (L.) W.D.J. Koch & Ziz
- Sinapis Arvensis L. var. schkuhriana (Rchb.) Hagenb.
- Sinapis Incana L.
- Sinapis Juncea L.
- Sinapis Nasturtiifolium Poir.
- Sinapis Nigra L.
- Singapore Graveyard Flower - Plumeria Obtusa L.
- Singapore Graveyard Flower - Plumeria Obtusa L. var. obtusa
- Singapore Graveyard Flower - Plumeria Obtusa L. var. sericifolia (C. Wright) Woodson
- Single Delight - Moneses Salisb. ex Gray
- Single Delight - Moneses Uniflora (L.) A. Gray
- Single Threeawn - Aristida Schiedeana Trin. & Rupr.
- Singleflower Cyrtandra - Cyrtandra Hematos H. St. John
- Singleflower Knapweed - Centaurea Uniflora Turra
- Singleflower Knapweed - Centaurea Uniflora Turra ssp. nervosa (Willd.) Bonnier & Layens
- Singlehead Goldenbush - Ericameria Suffruticosa (Nutt.) G.L. Nesom
- Singlehead Pussytoes - Antennaria Solitaria Rydb.
- Singleleaf Ash - Fraxinus Anomala Torr. ex S. Watson
- Singleleaf Ash - Fraxinus Anomala Torr. ex S. Watson var. anomala
- Singleleaf Ash - Fraxinus Anomala Torr. ex S. Watson var. lowellii (Sarg.) Little
- Singleleaf Pinyon - Pinus Monophylla Torr. & Frém.
- Singlelobe Twinsorus Fern - Diplazium Unilobum (Poir.) Hieron.
- Singlenerve Peperomia - Peperomia Hesperomannii Wawra
- Singlesorus Island Spleenwort - Diellia Unisora W.H. Wagner
- Singlesorus Spleenwort - Asplenium Monanthes L.
- Singlespike Peperomia - Peperomia Sandwicensis Miq.
- Singlestem Buckwheat - Eriogonum Acaule Nutt.
- Singlestem Leather-root - Orbexilum Simplex (Nutt. ex Torr. & A. Gray) Rydb.
- Singlewhorl Burrobrush - Hymenoclea Monogyra Torr. & A. Gray
- Sinkwa Towelsponge - Luffa Acutangula (L.) Roxb.
- Sinningia - Sinningia Nees
- Sinocalamus Oldhamii (Munro) McClure [excluded]
- Sintenis' Clubmoss - Huperzia Sintenisii (Herter) Holub
- Sintenis' Guava - Psidium Sintenisii (Kiaersk.) Alain
- Sintenis' Milkvine - Matelea Sintenisii (Schltr.) Woodson
- Sintenis' Peperomia - Peperomia Sintenisii C. DC.
- Sintenis' Quina - Antirhea Sintenisii Urb.
- Sintenis' Spike-rush - Eleocharis Debilis Kunth
- Sinuous Hypotrachyna Lichen - Hypotrachyna Sinuosa (Sm.) Hale
- Sipe's Kidney Lichen - Nephroma Helveticum Ach. ssp. sipeanum (Gyel.) Goward & Ahti
- Siphonanthus Indicus L.
- Siphonella Floribunda (A. Gray) Jeps.
- Siphoneugena - Siphoneugena Berg
- Siphonia Brasiliensis Willd. ex A. Juss.
- Siphonoglossa Dipteracantha (Nees) A. Heller
- Siphonoglossa Greggii Greenm. & C.H. Thomp.
- Siphonoglossa Longiflora (Torr.) A. Gray
- Siphonoglossa Pilosella (Nees) Torr.
- Siphonosmanthus Delavayi (Franch.) Stapf
- Siphonychia Americana (Nutt.) Torr. & A. Gray
- Siphonychia Diffusa Chapm.
- Siphonychia Erecta Chapm.
- Siphonychia Interior (Small) Core
- Siphonychia Pauciflora Small
- Siphonychia Rugellii Chapm.
- Siphula Simplex (Taylor) Nyl.
- Sisal Hemp - Agave Sisalana Perrine
- Siskiyou Beardtongue - Penstemon Anguineus Eastw.
- Siskiyou Bedstraw - Galium Ambiguum W. Wight ssp. siskiyouense (Ferris) Dempster & Stebbins
- Siskiyou Bluecurls - Trichostema Simulatum Jeps.
- Siskiyou Buckwheat - Eriogonum Siskiyouense Small
- Siskiyou Checkerbloom - Sidalcea Malviflora (DC.) A. Gray ex Benth. ssp. patula C.L. Hitchc.
- Siskiyou Clover - Trifolium Siskiyouense J.M. Gillett
- Siskiyou False Hellebore - Veratrum Insolitum Jeps.
- Siskiyou False Rue Anemone - Enemion Stipitatum (A. Gray) J.R. Drumm. & Hutch.
- Siskiyou Fleabane - Erigeron Cervinus Greene
- Siskiyou Fritillary - Fritillaria Glauca Greene
- Siskiyou Indian Paintbrush - Castilleja Miniata Douglas ex Hook. ssp. elata (Piper) Munz
- Siskiyou Iris - Iris Bracteata S. Watson
- Siskiyou Lewisia - Lewisia Cotyledon (S. Watson) B.L. Rob.
- Siskiyou Lewisia - Lewisia Cotyledon (S. Watson) B.L. Rob. var. cotyledon
- Siskiyou Mariposa Lily - Calochortus Persistens Ownbey
- Siskiyou Milkvetch - Astragalus Whitneyi A. Gray var. siskiyouensis (Rydb.) Barneby
- Siskiyou Monardella - Monardella Siskiyouensis Hardham
- Siskiyou Mountain Owl's-clover - Orthocarpus Cuspidatus Greene ssp. cuspidatus
- Siskiyou Mountain Ragwort - Packera Macounii (Greene) W.A. Weber & Á. Löve
- Siskiyou Mountain Woodland-star - Lithophragma Campanulatum Howell
- Siskiyou Onion - Allium Siskiyouense Ownbey
- Siskiyou Pennycress - Noccaea Fendleri (A. Gray) Holub ssp. siskiyouensis (P.K. Holmgren) Al-Shehbaz &
- Siskiyou Phacelia - Phacelia Leonis J.T. Howell
- Siskiyou Sedge - Carex Scabriuscula Mack.
- Siskiyou Splashzone Moss - Scouleria Siskiyouensis Shevock & D.H. Norris
- Siskiyou Willowherb - Epilobium Siskiyouense (Munz) Hoch & P.H. Raven
- Sisymbrium Alliaria (L.) Scop.
- Sisymbrium Ambiguum (S. Watson) Payson
- Sisymbrium Amphibium L.
- Sisymbrium Aureum (Eastw.) Payson
- Sisymbrium Brachycarpum Richardson
- Sisymbrium Curvisiliqua Hook.
- Sisymbrium Dentatum Torr.
- Sisymbrium Elegans (M.E. Jones) Payson
- Sisymbrium Elegans (M.E. Jones) Payson var. juniperorum (Payson) Harrington
- Sisymbrium Humile C.A. Mey.
- Sisymbrium Incanum Bernh. ex Fisch. & C.A. Mey.
- Sisymbrium Incisum Engelm. ex A. Gray
- Sisymbrium Incisum Engelm. ex A. Gray var. filipes A. Gray
- Sisymbrium Indicum L.
- Sisymbrium Juniperorum Payson
- Sisymbrium Kearneyi Rollins
- Sisymbrium Linearifolium (A. Gray) Payson
- Sisymbrium Linifolium (Nutt.) Nutt. ex Torr. & A. Gray
- Sisymbrium Longipedicellatum Fourn.
- Sisymbrium Microtites B.L. Rob.
- Sisymbrium Murale L.
- Sisymbrium Nasturtium-aquaticum L.
- Sisymbrium Officinale (L.) Scop. var. leiocarpum DC.
- Sisymbrium Pinnatum (Walter) Greene
- Sisymbrium Purpusii (Brandegee) O.E. Schulz
- Sisymbrium Salsugineum Pall.
- Sisymbrium Shinnersii M.C. Johnst.
- Sisymbrium Sophia L.
- Sisymbrium Sophioides Fisch. ex Hook.
- Sisymbrium Tenuifolium L.
- Sisymbrium Thalianum (L.) J. Gay & Monn.
- Sisymbrium Vaseyi S. Watson ex B.L. Rob.
- Sisymbrium Vernale (Wooton & Standl.) O.E. Schulz
- Sisymbrium Virgatum Nutt.
- Sisymbrium Viscosum (Rydb.) Blank.
- Sisyrinchium Apiculatum E.P. Bicknell
- Sisyrinchium Arenicola E.P. Bicknell
- Sisyrinchium Asheianum E.P. Bicknell
- Sisyrinchium Bermudiana L. var. crebrum (Fernald) B. Boivin
- Sisyrinchium Bermudiana auct. non L.
- Sisyrinchium Birameum Piper
- Sisyrinchium Boreale (E.P. Bicknell) Henry
- Sisyrinchium Brayi E.P. Bicknell
- Sisyrinchium Brownei Small
- Sisyrinchium Bulbosum Mill.
- Sisyrinchium Campestre E.P. Bicknell var. kansanum E.P. Bicknell
- Sisyrinchium Canbyi E.P. Bicknell
- Sisyrinchium Carolinianum E.P. Bicknell
- Sisyrinchium Colubriferum E.P. Bicknell
- Sisyrinchium Demissum Greene var. amethystinum (E.P. Bicknell) Kearney & Peebles
- Sisyrinchium Dimorphum R.L. Oliv.
- Sisyrinchium Douglasii A. Dietr.
- Sisyrinchium Douglasii A. Dietr. var. inflatum (Suksd.) P.K. Holmgren
- Sisyrinchium Eastwoodiae E.P. Bicknell
- Sisyrinchium Ensigerum E.P. Bicknell
- Sisyrinchium Exile E.P. Bicknell
- Sisyrinchium Fibrosum E.P. Bicknell
- Sisyrinchium Flaviflorum E.P. Bicknell
- Sisyrinchium Floridanum E.P. Bicknell
- Sisyrinchium Graminoides E.P. Bicknell
- Sisyrinchium Greenei E.P. Bicknell
- Sisyrinchium Hastile E.P. Bicknell p.p.
- Sisyrinchium Helleri E.P. Bicknell
- Sisyrinchium Hesperium E.P. Bicknell
- Sisyrinchium Heterocarpum E.P. Bicknell
- Sisyrinchium Inalatum A. Nelson
- Sisyrinchium Incrustatum E.P. Bicknell
- Sisyrinchium Inflatum (Suksd.) H. St. John
- Sisyrinchium Intermedium E.P. Bicknell
- Sisyrinchium Kansanum (E.P. Bicknell) Alexander
- Sisyrinchium Laxum Otto ex Sims
- Sisyrinchium Longipedunculatum E.P. Bicknell
- Sisyrinchium Macounii E.P. Bicknell
- Sisyrinchium Micranthum auct. non Cav.
- Sisyrinchium Montanum Greene ssp. crebrum (Fernald) Böcher
- Sisyrinchium Mucronatum Michx. var. atlanticum (E.P. Bicknell) H.E. Ahles
- Sisyrinchium Occidentale E.P. Bicknell
- Sisyrinchium Powellii Warnock
- Sisyrinchium Pruinosum E.P. Bicknell
- Sisyrinchium Rufipes E.P. Bicknell
- Sisyrinchium Scabrellum E.P. Bicknell
- Sisyrinchium Scabrum Cham. & Schltdl.
- Sisyrinchium Segetum E.P. Bicknell
- Sisyrinchium Solstitiale E.P. Bicknell
- Sisyrinchium Strictum E.P. Bicknell
- Sisyrinchium Tortum E.P. Bicknell
- Sisyrinchium Varians E.P. Bicknell
- Sitanion Anomalum J.G. Sm.
- Sitanion Elymoides Raf.
- Sitanion Hansenii (Scribn.) J.G. Sm.
- Sitanion Hordeoides Suksd.
- Sitanion Hystrix (Nutt.) J.G. Sm.
- Sitanion Hystrix (Nutt.) J.G. Sm. var. brevifolium (J.G. Sm.) C.L. Hitchc.
- Sitanion Hystrix (Nutt.) J.G. Sm. var. californicum (J.G. Sm.) F.D. Wilson
- Sitanion Hystrix (Nutt.) J.G. Sm. var. hordeoides (Suksd.) C.L. Hitchc.
- Sitanion Jubatum J.G. Sm.
- Sitanion Longifolium J.G. Sm.
- Sitanion Velutinum Piper
- Sitilias Caroliniana (Walter) Raf.
- Sitilias Grandiflora (Nutt.) Greene
- Sitilias Multicaulis (DC.) Greene
- Sitka Alder - Alnus Viridis (Chaix) DC. ssp. sinuata (Regel) Á. Löve & D. Löve
- Sitka Clubmoss - Lycopodium Sitchense Rupr.
- Sitka Mistmaiden - Romanzoffia Sitchensis Bong.
- Sitka Mountain Ash - Sorbus Sitchensis M. Roem. var. sitchensis
- Sitka Rockbrake - Cryptogramma Sitchensis (Rupr.) T. Moore
- Sitka Sedge - Carex Aquatilis Wahlenb. var. dives (T. Holm) Kük.
- Sitka Shield Lichen - Heterodermia Sitchensis Goward & W. Noble
- Sitka Spruce - Picea Sitchensis (Bong.) Carrière
- Sitka Starwort - Stellaria Borealis Bigelow ssp. sitchana (Steud.) Piper
- Sitka Valerian - Valeriana Sitchensis Bong.
- Sitka Willow - Salix Sitchensis Sanson ex Bong.
- Sitodium Altile Parkinson
- Sium Cicutifolium Schrank
- Sium Floridanum Small
- Sium Suave Walter var. floridanum (Small) C.F. Reed
- Sivinsk's Erigeron - Erigeron Sivinskii G.L. Nesom
- Sixangle Foldwing - Dicliptera Sexangularis (L.) Juss.
- Sixangle Pipewort - Eriocaulon Sexangulare L.
- Sixangle Spurge - Euphorbia Hexagona Nutt. ex Spreng.
- Sixweeks Fescue - Vulpia Octoflora (Walter) Rydb.
- Sixweeks Fescue - Vulpia Octoflora (Walter) Rydb. var. glauca (Nutt.) Fernald
- Sixweeks Fescue - Vulpia Octoflora (Walter) Rydb. var. hirtella (Piper) Henr.
- Sixweeks Fescue - Vulpia Octoflora (Walter) Rydb. var. octoflora
- Sixweeks Grama - Bouteloua Barbata Lag.
- Sixweeks Lovegrass - Eragrostis Lutescens Scribn.
- Sixweeks Muhly - Muhlenbergia Depauperata Scribn.
- Sixweeks Prairie Clover - Dalea Polygonoides A. Gray
- Sixweeks Threeawn - Aristida Adscensionis L.
- Skeletongrass - Gymnopogon P. Beauv.
- Skeletonleaf Bur Ragweed - Ambrosia Tomentosa Nutt.
- Skeletonleaf Willow - Salix Phlebophylla Andersson
- Skeletonplant - Lygodesmia D. Don
- Skeletonweed - Chaetadelpha A. Gray ex S. Watson
- Skeletonweed - Pleiacanthus Rydb.
- Skiff Milkvetch - Astragalus Microcymbus Barneby
- Skilpadbessie - Nylandtia Spinosa (L.) Dumort.
- Skimmia - Skimmia Thunb.
- Skin Lichen - Leptogium (ach.) A. Gray
- Skin Lichen - Leptogium Adpressum Nyl.
- Skin Lichen - Leptogium Byssinum (Hoffm.) Zwackh ex Nyl.
- Skin Lichen - Leptogium Chloromelum (Sw. ex Ach.) Nyl.
- Skin Lichen - Leptogium Corniculatum (Hoffm.) Minks
- Skin Lichen - Leptogium Corticola (Taylor) Tuck.
- Skin Lichen - Leptogium Cyanescens (Rabenh.) Körb.
- Skin Lichen - Leptogium Dactylinum Tuck.
- Skin Lichen - Leptogium Furfuraceum (Harm.) Sierk
- Skin Lichen - Leptogium Fusisporum (Tuck.) C.W. Dodge
- Skin Lichen - Leptogium Hypotrachynum Müll. Arg.
- Skin Lichen - Leptogium Isidiosellum (Riddle) Sierk
- Skin Lichen - Leptogium Laceroides (de Lesd.) P.M. Jørg.
- Skin Lichen - Leptogium Lichenoides (L.) Zahlbr.
- Skin Lichen - Leptogium Marginellum (Sw.) A. Gray
- Skin Lichen - Leptogium Microstictum Vain.
- Skin Lichen - Leptogium Milligranum Sierk
- Skin Lichen - Leptogium Parculum Nyl.
- Skin Lichen - Leptogium Phyllocarpum (Pers.) Mont.
- Skin Lichen - Leptogium Platynum (Tuck.) Herre
- Skin Lichen - Leptogium Plicatile (Ach.) Leight.
- Skin Lichen - Leptogium Rivale Tuck.
- Skin Lichen - Leptogium Rivulare (Ach.) Mont.
- Skin Lichen - Leptogium Tenuissimum (Dicks.) Körb.
- Skinner's False Foxglove - Agalinis Skinneriana (Alph. Wood) Britton
- Skirret - Sium Sisarum L.
- Skottsberg's False Ohelo - Wikstroemia Skottsbergiana Sparre
- Skottsbergiliana Lasiocephala (Skottsb.) H. St. John
- Skullcap - Scutellaria L.
- Skullcap - Scutellaria ×churchilliana Fernald (pro sp.)
- Skullcap Speedwell - Veronica Scutellata L.
- Skult's Shield Lichen - Parmelia Skultii Hale
- Skunk Cabbage - Symplocarpus Foetidus (L.) Salisb. ex W.P.C. Barton
- Skunk Cabbage - Symplocarpus Salisb. ex W.P.C. Barton
- Skunk Currant - Ribes Glandulosum Grauer
- Skunkbush - Navarretia Squarrosa (Eschsch.) Hook. & Arn.
- Skunkbush Sumac - Rhus Trilobata Nutt.
- Skunkbush Sumac - Rhus Trilobata Nutt. var. anisophylla (Greene) Jeps.
- Skunkbush Sumac - Rhus Trilobata Nutt. var. quinata (Greene) Jeps.
- Skunkbush Sumac - Rhus Trilobata Nutt. var. racemulosa (Greene) F.A. Barkley
- Skunkbush Sumac - Rhus Trilobata Nutt. var. simplicifolia (Greene) F.A. Barkley
- Skunkbush Sumac - Rhus Trilobata Nutt. var. trilobata
- Skunkcabbage - Lysichiton Schott
- Skunktop - Pediomelum Mephiticum (S. Watson) Rydb.
- Sky Lupine - Lupinus Nanus Douglas ex Benth.
- Sky Lupine - Lupinus Nanus Douglas ex Benth. ssp. latifolius (Benth. ex Torr.) D. Dunn
- Sky Lupine - Lupinus Nanus Douglas ex Benth. ssp. nanus
- Sky Mousetail - Ivesia Shockleyi S. Watson
- Sky Mousetail - Ivesia Shockleyi S. Watson var. shockleyi
- Sky Plant - Tillandsia Ionantha Planch.
- Sky-blue Lupine - Lupinus Cumulicola Small
- Skyblue Aster - Symphyotrichum Oolentangiense (Riddell) G.L. Nesom
- Skyblue Aster - Symphyotrichum Oolentangiense (Riddell) G.L. Nesom var. oolentangiense
- Skyblue Aster - Symphyotrichum Oolentangiense (Riddell) G.L. Nesom var. poaceum (Burgess) G.L. Nesom
- Skyblue Clustervine - Jacquemontia Pentanthos (Jacq.) G. Don
- Skyblue Phacelia - Phacelia Coerulea Greene
- Skyflower - Hydrolea Corymbosa J. Macbr. ex Elliott
- Skypilot - Polemonium Eximium Greene
- Skyttea Elachistophora (Nyl.) Sherwood & D. Hawksw.
- Skyttea Sherwood, D. Hawksw. & Coppins
- Skyttella Lichen - Skyttella D. Hawksw. & R. Sant.
- Slash Pine - Pinus Elliottii Engelm.
- Slash Pine - Pinus Elliottii Engelm. var. elliottii
- Slashleaf Slipplejack - Serjania Incisa Torr.
- Slaty Gum - Eucalyptus Dawsonii R.T. Baker
- Sleeping Combseed - Pectocarya Penicillata (Hook. & Arn.) A. DC.
- Sleeping Popcornflower - Plagiobothrys Scouleri (Hook. & Arn.) I.M. Johnst. var. hispidulus (Greene) Dorn
- Sleeping Ute Milkvetch - Astragalus Tortipes J.L. Anderson & J.M. Porter
- Sleepingbeauty Waterlily - Nymphaea Glandulifera Rodschied [excluded]
- Sleepy Silene - Silene Antirrhina L.
- Sleepydaisy - Xanthisma Dc.
- Sleepygrass - Achnatherum Robustum (Vasey) Barkworth
- Slender Amaranth - Amaranthus Viridis L.
- Slender Arrowgrass - Triglochin Concinna Burtt Davy
- Slender Arrowhead - Sagittaria Teres S. Watson
- Slender Aster - Eurybia Compacta G.L. Nesom
- Slender Beaksedge - Rhynchospora Gracilenta A. Gray
- Slender Bedstraw - Galium Angustifolium Nutt. ex A. Gray ssp. gracillimum Dempster & Stebbins
- Slender Bird's Beak - Cordylanthus Tenuis A. Gray
- Slender Bird's Beak - Cordylanthus Tenuis A. Gray ssp. tenuis
- Slender Bird's Beak - Cordylanthus Tenuis A. Gray ssp. viscidus (Howell) T.I. Chuang & Heckard
- Slender Bird's-foot Trefoil - Lotus Angustissimus L.
- Slender Blazing Star - Liatris Gracilis Pursh
- Slender Blue Iris - Iris Prismatica Pursh ex Ker Gawl.
- Slender Bluestem - Dichanthium Tenue (R. Br.) A. Camus
- Slender Bog Orchid - Platanthera Stricta Lindl.
- Slender Bottle-washers - Enneapogon Gracilis (R. Br.) P. Beauv.
- Slender Brake - Pteris Ensiformis Burm. f.
- Slender Buckwheat - Eriogonum Microthecum Nutt.
- Slender Buckwheat - Eriogonum Microthecum Nutt. var. ambiguum (M.E. Jones) Reveal
- Slender Buckwheat - Eriogonum Microthecum Nutt. var. lapidicola Reveal
- Slender Buckwheat - Eriogonum Microthecum Nutt. var. laxiflorum Hook.
- Slender Buckwheat - Eriogonum Microthecum Nutt. var. microthecum
- Slender Bulrush - Schoenoplectus Heterochaetus (Chase) Soják
- Slender Bunchflower - Veratrum Hybridum (Walter) J.H. Zimmerman ex Zomlefer
- Slender Bushmallow - Malacothamnus Jonesii (Munz) Kearney
- Slender Buttonweed - Diodia Ocymifolia (Willd. ex Roem. & Schult.) Bremek.
- Slender Carpetweed - Mollugo Gracillima Andersson
- Slender Centaury - Centaurium Tenuiflorum (Hoffmanns. & Link) Fritsch
- Slender Chickweed - Cerastium Gracile Dufour
- Slender Cinquefoil - Potentilla Gracilis Douglas ex Hook.
- Slender Cinquefoil - Potentilla Gracilis Douglas ex Hook. var. brunnescens (Rydb.) C.L. Hitchc.
- Slender Cinquefoil - Potentilla Gracilis Douglas ex Hook. var. fastigiata (Nutt.) S. Watson
- Slender Cinquefoil - Potentilla Gracilis Douglas ex Hook. var. flabelliformis (Lehm.) Nutt. ex Torr. & A.
- Slender Clarkia - Clarkia Gracilis (Piper) A. Nelson & J.F. Macbr.
- Slender Clarkia - Clarkia Gracilis (Piper) A. Nelson & J.F. Macbr. ssp. gracilis
- Slender Cleomella - Cleomella Parviflora A. Gray
- Slender Clubmoss - Lycopodiella Caroliniana (L.) Pic. Serm.
- Slender Clubmoss - Lycopodiella Caroliniana (L.) Pic. Serm. var. caroliniana
- Slender Clubmoss - Lycopodiella Caroliniana (L.) Pic. Serm. var. meridionalis (Underw. & Lloyd) B. Pllg. & W
- Slender Cottongrass - Eriophorum Gracile W.D.J. Koch
- Slender Cottongrass - Eriophorum Gracile W.D.J. Koch var. caurianum Fernald
- Slender Cottongrass - Eriophorum Gracile W.D.J. Koch var. gracile
- Slender Crabgrass - Digitaria Filiformis (L.) Koeler
- Slender Creeping-oxeye - Sphagneticola Gracilis (Rich.) Pruski
- Slender Cryptantha - Cryptantha Sparsiflora (Greene) Greene
- Slender Cudweed - Gnaphalium Exilifolium A. Nelson
- Slender Cyclanthera - Cyclanthera Gracillima Cogn.
- Slender Ditch Paspalum - Paspalum Secans Hitchc. & Chase
- Slender Dodder - Cuscuta Leptantha Engelm.
- Slender Draba - Draba Albertina Greene
- Slender Dropseed - Sporobolus Creber De Nardi
- Slender Dwarf Morning-glory - Evolvulus Alsinoides (L.) L.
- Slender Dwarf Morning-glory - Evolvulus Alsinoides (L.) L. var. angustifolius Torr.
- Slender Dwarf Morning-glory - Evolvulus Alsinoides (L.) L. var. debilis (Kunth) van Ooststr.
- Slender Dwarf-flax - Hesperolinon Spergulinum (A. Gray) Small
- Slender False Brome - Brachypodium Sylvaticum (Huds.) P. Beauv.
- Slender False Buttonweed - Spermacoce Tenuior L.
- Slender False Dragonhead - Physostegia Intermedia (Nutt.) Engelm. & A. Gray
- Slender False Garlic - Nothoscordum Gracile (Aiton) Stearn
- Slender False Pennyroyal - Hedeoma Acinoides Scheele
- Slender Fimbry - Fimbristylis Autumnalis (L.) Roem. & Schult.
- Slender Flatsedge - Cyperus Bipartitus Torr.
- Slender Fleabane - Erigeron Tener (A. Gray) A. Gray
- Slender Goldenbanner - Thermopsis Gracilis Howell
- Slender Goldenbanner - Thermopsis Gracilis Howell var. gracilis
- Slender Goldenbanner - Thermopsis Gracilis Howell var. ovata (B.L. Rob. ex Piper) M. Mendenhall
- Slender Goldentop - Euthamia Caroliniana (L.) Greene ex Porter & Britton
- Slender Goldentop - Euthamia Galetorum Greene
- Slender Goldenweed - Machaeranthera Gracilis (Nutt.) Shinners
- Slender Goldshower - Galphimia Gracilis Bartlett
- Slender Grama - Bouteloua Repens (Kunth) Scribn. & Merr.
- Slender Grasswort - Salicornia Maritima Wolff & Jefferies
- Slender Greenthread - Thelesperma Simplicifolium A. Gray
- Slender Hairgrass - Deschampsia Elongata (Hook.) Munro
- Slender Hawksbeard - Crepis Atribarba A. Heller
- Slender Hawksbeard - Crepis Atribarba A. Heller ssp. atribarba
- Slender Hawksbeard - Crepis Atribarba A. Heller ssp. originalis (Babc. & Stebbins) Babc. & Stebbins
- Slender Hawkweed - Hieracium Gracile Hook.
- Slender Hawkweed - Hieracium Gracile Hook. var. gracile
- Slender Hawthorn - Crataegus Exilis Beadle
- Slender Hop Clover - Trifolium Micranthum Viv.
- Slender Indiangrass - Sorghastrum Elliottii (C. Mohr) Nash
- Slender Janusia - Janusia Gracilis A. Gray
- Slender Leaf Rattlebox - Crotalaria Ochroleuca G. Don
- Slender Lespedeza - Lespedeza Virginica (L.) Britton
- Slender Lipfern - Cheilanthes Feei T. Moore
- Slender Little Bluestem - Schizachyrium Tenerum Nees
- Slender Looseflower Sedge - Carex Gracilescens Steud.
- Slender Mariposa Lily - Calochortus Clavatus S. Watson var. gracilis Ownbey
- Slender Meadow Foxtail - Alopecurus Myosuroides Huds.
- Slender Meadowfoam - Limnanthes Gracilis Howell
- Slender Meadowfoam - Limnanthes Gracilis Howell ssp. gracilis
- Slender Milkvetch - Astragalus Gracilis Nutt.
- Slender Monkeyflower - Mimulus Leptaleus A. Gray
- Slender Mountain Sandwort - Arenaria Capillaris Poir.
- Slender Mountain Sandwort - Arenaria Capillaris Poir. ssp. capillaris
- Slender Muhly - Muhlenbergia Tenuifolia (Kunth) Trin.
- Slender Myoporum - Myoporum Parvifolium R. Br.
- Slender Nutrush - Scleria Minor W. Stone
- Slender Oat - Avena Barbata Pott ex Link
- Slender Orcutt Grass - Orcuttia Tenuis Hitchc.
- Slender Panicgrass - Ottochloa Nodosa (Kunth) Dandy
- Slender Panicgrass - Panicum Capillarioides Vasey
- Slender Parsley Piert - Aphanes Microcarpa (Boiss. & Reut.) Rothm.
- Slender Passionflower - Passiflora Filipes Benth.
- Slender Penstemon - Penstemon Gracilentus A. Gray
- Slender Phlox - Microsteris Gracilis (Hook.) Greene
- Slender Phlox - Microsteris Gracilis (Hook.) Greene var. gracilis
- Slender Phlox - Microsteris Gracilis (Hook.) Greene var. humilior (Hook.) Cronquist
- Slender Pinepink - Bletia Florida (Salisb.) R. Br.
- Slender Plantain - Plantago Heterophylla Nutt.
- Slender Popcornflower - Plagiobothrys Tener (Greene) I.M. Johnst.
- Slender Popcornflower - Plagiobothrys Tener (Greene) I.M. Johnst. var. subglaber I.M. Johnst.
- Slender Popcornflower - Plagiobothrys Tener (Greene) I.M. Johnst. var. tener
- Slender Poreleaf - Porophyllum Gracile Benth.
- Slender Pride Of Rochester - Deutzia Gracilis Siebold & Zucc.
- Slender Rattlesnakeroot - Prenanthes Autumnalis Walter
- Slender Rose Gentian - Sabatia Campanulata (L.) Torr.
- Slender Rosette Grass - Dichanthelium Xanthophysum (A. Gray) Freckmann
- Slender Rosinweed - Silphium Gracile A. Gray
- Slender Rushpea - Hoffmannseggia Tenella Tharp & L.O. Williams
- Slender Russian Thistle - Salsola Collina Pall.
- Slender Saltbush - Atriplex Tenuissima A. Nelson
- Slender Sand Verbena - Abronia Gracilis Benth.
- Slender Sandbur - Cenchrus Gracillimus Nash
- Slender Scratchdaisy - Croptilon Divaricatum (Nutt.) Raf.
- Slender Seapurslane - Sesuvium Maritimum (Walter) Britton, Sterns & Poggenb.
- Slender Sedge - Carex Gracilior Mack.
- Slender Sensitive Pea - Chamaecrista Serpens (L.) Greene
- Slender Sensitive Pea - Chamaecrista Serpens (L.) Greene var. serpens
- Slender Snakecotton - Froelichia Gracilis (Hook.) Moq.
- Slender Soft Brome - Bromus Lepidus Holmb.
- Slender Sowthistle - Sonchus Tenerrimus L.
- Slender Spiderflower - Cleome Multicaulis DC.
- Slender Spiderling - Boerhavia Triquetra S. Watson
- Slender Spikerush - Eleocharis Tenuis (Willd.) Schult.
- Slender Spikerush - Eleocharis Tenuis (Willd.) Schult. var. pseudoptera (Weath. ex Svens.) Svens.
- Slender Spikerush - Eleocharis Tenuis (Willd.) Schult. var. tenuis
- Slender Spikerush - Eleocharis Tenuis (Willd.) Schult. var. verrucosa (Svens.) Svens.
- Slender Stitchwort - Minuartia Tenella (Nutt.) Mattf.
- Slender Sunflower - Helianthus Gracilentus A. Gray
- Slender Tansyaster - Psilactis Tenuis S. Watson
- Slender Tarweed - Madia Subspicata D.D. Keck
- Slender Threadplant - Nemacladus Gracilis Eastw.
- Slender Threeseed Mercury - Acalypha Gracilens A. Gray
- Slender Threeseed Mercury - Acalypha Monococca (Engelm. ex A. Gray) Lill. W. Mill. & Gandhi
- Slender Toothwort - Cardamine Angustata O.E. Schulz
- Slender Vetch - Vicia Laxiflora Brot.
- Slender Watermilfoil - Myriophyllum Tenellum Bigelow
- Slender Waternymph - Najas Gracillima (A. Braun ex Engelm.) Magnus
- Slender Wedgescale - Sphenopholis Intermedia (Rydb.) Rydb.
- Slender Wheatgrass - Elymus Trachycaulus (Link) Gould ex Shinners
- Slender Wheatgrass - Elymus Trachycaulus (Link) Gould ex Shinners ssp. subsecundus (Link) Á. Löve & D. Lö
- Slender Wheatgrass - Elymus Trachycaulus (Link) Gould ex Shinners ssp. trachycaulus
- Slender Wheatgrass - Elymus Trachycaulus (Link) Gould ex Shinners ssp. virescens (Lange) Á. Löve & D. Löv
- Slender Wild Basil - Clinopodium Gracile (Benth.) Kuntze
- Slender Wild Cabbage - Caulanthus Major (M.E. Jones) Payson
- Slender Wild Cabbage - Caulanthus Major (M.E. Jones) Payson var. major
- Slender Wild Cabbage - Caulanthus Major (M.E. Jones) Payson var. nevadensis Rollins
- Slender Wildparsley - Musineon Tenuifolium (Nutt. ex Torr. & A. Gray) J.M. Coult. & Rose
- Slender Woodland Sedge - Carex Digitalis Willd.
- Slender Woodland Sedge - Carex Digitalis Willd. var. digitalis
- Slender Woodland Sedge - Carex Digitalis Willd. var. floridana (L.H. Bailey) Naczi & Bryson
- Slender Woodland Sedge - Carex Digitalis Willd. var. macropoda Fernald
- Slender Woodland-star - Lithophragma Tenellum Nutt.
- Slender Woodoats - Chasmanthium Laxum (L.) Yates
- Slender Woolly Buckwheat - Eriogonum Gracile Benth.
- Slender Woolly Buckwheat - Eriogonum Gracile Benth. var. gracile
- Slender Woolly Buckwheat - Eriogonum Gracile Benth. var. incultum Reveal
- Slender Woollyheads - Psilocarphus Tenellus Nutt.
- Slender Woollyheads - Psilocarphus Tenellus Nutt. var. globiferus (Bertero ex DC.) Morefield
- Slender Woollyheads - Psilocarphus Tenellus Nutt. var. tenellus
- Slender Yellow Woodsorrel - Oxalis Dillenii Jacq.
- Slender Yelloweyed Grass - Xyris Torta Sm.
- Slender-fruit Beaksedge - Rhynchospora Leptocarpa (Chapm. ex Britton) Small
- Slender-fruit Saltbush - Atriplex Leptocarpa F. Muell.
- Slender-leaf Sandwort - Minuartia Hybrida (Vill.) Schischk.
- Slender-spire Orchid - Piperia Unalascensis (Spreng.) Rydb.
- Slenderbeak Sedge - Carex Athrostachya Olney
- Slendercluster Wild Coffee - Psychotria Leptothyrsa Miq.
- Slendercluster Wild Coffee - Psychotria Leptothyrsa Miq. var. longicarpa Valeton
- Slenderflower Saltbush - Atriplex Graciliflora M.E. Jones
- Slenderfruit Nutrush - Scleria Georgiana Core
- Slenderfruit Willowherb - Epilobium Leptocarpum Hausskn.
- Slenderhorn Spineflower - Dodecahema Leptoceras (A. Gray ex Benth.) Reveal & Hardham
- Slenderleaf Buckwheat - Eriogonum Leptophyllum (Torr. & A. Gray) Wooton & Standl.
- Slenderleaf Bundleflower - Desmanthus Leptophyllus Kunth
- Slenderleaf Clammyweed - Polanisia Tenuifolia Torr. & A. Gray
- Slenderleaf False Dragonhead - Physostegia Leptophylla Small
- Slenderleaf False Foxglove - Agalinis Tenuifolia (Vahl) Raf.
- Slenderleaf False Foxglove - Agalinis Tenuifolia (Vahl) Raf. var. leucanthera (Raf.) Pennell
- Slenderleaf False Foxglove - Agalinis Tenuifolia (Vahl) Raf. var. macrophylla (Benth.) S.F. Blake
- Slenderleaf False Foxglove - Agalinis Tenuifolia (Vahl) Raf. var. parviflora (Nutt.) Pennell
- Slenderleaf False Foxglove - Agalinis Tenuifolia (Vahl) Raf. var. polyphylla (Small) Pennell
- Slenderleaf False Foxglove - Agalinis Tenuifolia (Vahl) Raf. var. tenuifolia
- Slenderleaf Fleabane - Erigeron Tenuis Torr. & A. Gray
- Slenderleaf Iceplant - Mesembryanthemum Nodiflorum L.
- Slenderleaf Lomatium - Lomatium Simplex (Nutt.) J.F. Macbr. var. leptophyllum (Hook.) Mathias
- Slenderleaf Sage - Salvia Reptans Jacq.
- Slenderleaf Skyrocket - Ipomopsis Tenuifolia (A. Gray) V.E. Grant
- Slenderleaf Sundew - Drosera Linearis Goldie
- Slenderlobe Bundleflower - Desmanthus Leptolobus Torr. & A. Gray
- Slenderpetal Thelypody - Thelypodium Stenopetalum S. Watson
- Slenderstalk Beeblossom - Oenothera Filipes (Spach) W.L. Wagner & Hoch
- Slenderstalk Monkeyflower - Mimulus Gracilipes B.L. Rob.
- Slenderstem Lessingia - Lessingia Nemaclada Greene
- Slenderstem Lessingia - Lessingia Nemaclada Greene var. albiflora (Eastw.) J.T. Howell
- Slenderstem Lessingia - Lessingia Nemaclada Greene var. nemaclada
- Slenderstem Monkeyflower - Mimulus Filicaulis S. Watson
- Slendertube Skyrocket - Ipomopsis Tenuituba (Rydb.) V.E. Grant
- Slendertube Skyrocket - Ipomopsis Tenuituba (Rydb.) V.E. Grant ssp. latiloba V.E. Grant & Wilken
- Slendertube Skyrocket - Ipomopsis Tenuituba (Rydb.) V.E. Grant ssp. tenuituba
- Slickrock Biscuitroot - Lomatium Laevigatum (Nutt.) J.M. Coult. & Rose
- Slickseed Fuzzybean - Strophostyles Leiosperma (Torr. & A. Gray) Piper
- Slightstemmed Miterwort - Mitella Caulescens Nutt.
- Slim Amaranth - Amaranthus Hybridus L.
- Slim Larkspur - Delphinium Depauperatum Nutt.
- Slim Milkweed - Asclepias Linearis Scheele
- Slim Spikerush - Eleocharis Elongata Chapm.
- Slim Tridens - Tridens Muticus (Torr.) Nash
- Slim Tridens - Tridens Muticus (Torr.) Nash var. elongatus (Buckley) Shinners
- Slim Tridens - Tridens Muticus (Torr.) Nash var. muticus
- Slimbristle Sandbur - Cenchrus Brownii Roem. & Schult.
- Slimflower Lovegrass - Eragrostis Gangetica (Roxb.) Steud.
- Slimflower Muhly - Muhlenbergia Tenuiflora (Willd.) Britton, Sterns & Poggenb.
- Slimflower Scurfpea - Psoralidium Tenuiflorum (Pursh) Rydb.
- Slimfoot Century Plant - Agave Gracilipes Trel.
- Slimjim Bean - Phaseolus Filiformis Benth.
- Slimjim Flatsedge - Cyperus Gracilis R. Br.
- Slimleaf Bean - Phaseolus Angustissimus A. Gray
- Slimleaf Bur Ragweed - Ambrosia Tenuifolia Spreng.
- Slimleaf Drymary - Drymaria Molluginea (Lag.) Didr.
- Slimleaf Goosefoot - Chenopodium Pallescens Standl.
- Slimleaf Heliotrope - Heliotropium Torreyi I.M. Johnst.
- Slimleaf Milkweed - Asclepias Stenophylla A. Gray
- Slimleaf Panicgrass - Dichanthelium Linearifolium (Scribn. ex Nash) Gould
- Slimleaf Pawpaw - Asimina Angustifolia Raf.
- Slimleaf Plainsmustard - Schoenocrambe Linearifolia (A. Gray) Rollins
- Slimleaf Prairie Clover - Dalea Tenuifolia (A. Gray) Shinners
- Slimleaf Rosewood - Vauquelinia Corymbosa Humb. & Bonpl.
- Slimleaf Rosewood - Vauquelinia Corymbosa Humb. & Bonpl. ssp. angustifolia (Rydb.) Hess & Henrickson
- Slimleaf Sneezeweed - Helenium Linifolium Rydb.
- Slimleaf Ticktrefoil - Desmodium Tenuifolium Torr. & A. Gray
- Slimlobe Bahia - Bahia Biternata A. Gray
- Slimlobe Beggarticks - Bidens Tenuisecta A. Gray
- Slimlobe Globeberry - Ibervillea Tenuisecta (A. Gray) Small
- Slimpod Milkweed - Asclepias Quinquedentata A. Gray
- Slimpod Rush - Juncus Diffusissimus Buckley
- Slimpod Venus' Looking-glass - Triodanis Leptocarpa (Nutt.) Nieuwl.
- Slimseed Sandmat - Chamaesyce Stictospora (Engelm.) Small
- Slimspike Prairie Clover - Dalea Phleoides (Torr. & A. Gray) Shinners
- Slimspike Prairie Clover - Dalea Phleoides (Torr. & A. Gray) Shinners var. microphylla (Torr. & A. Gray) Ba
- Slimspike Prairie Clover - Dalea Phleoides (Torr. & A. Gray) Shinners var. phleoides
- Slimspike Threeawn - Aristida Longespica Poir.
- Slimspike Threeawn - Aristida Longespica Poir. var. geniculata (Raf.) Fernald
- Slimspike Threeawn - Aristida Longespica Poir. var. longespica
- Slimspike Windmill Grass - Chloris Andropogonoides Fourn.
- Slimstalk Spiderling - Boerhavia Gracillima Heimerl
- Slimstem Muhly - Muhlenbergia Filiculmis Vasey
- Slimstem Reedgrass - Calamagrostis Stricta (Timm) Koeler
- Slimstem Reedgrass - Calamagrostis Stricta (Timm) Koeler ssp. stricta
- Slimstem Reedgrass - Calamagrostis Stricta (Timm) Koeler ssp. stricta var. borealis (Laest.) Hartm.
- Slimstem Reedgrass - Calamagrostis Stricta (Timm) Koeler ssp. stricta var. stricta
- Slipper Flower - Calceolaria L.
- Slipper Flower - Calceolaria Multiflora Cav.
- Slippery Burr - Corchorus Siliquosus L.
- Slippery Elm - Ulmus Rubra Muhl.
- Sloane's Tribisee - Lasiacis Sloanei (Griseb.) Hitchc.
- Sloe - Reynosia Uncinata Urb.
- Slough Sedge - Carex Obnupta L.H. Bailey
- Slough Thistle - Cirsium Crassicaule (Greene) Jeps.
- Sloughgrass - Beckmannia Host
- Slugwood - Beilschmiedia Pendula (Sw.) Hemsl.
- Small Archidium Moss - Archidium Minus (Renauld & Cardot) Snider
- Small Baby Blue Eyes - Nemophila Heterophylla Fisch. & C.A. Mey.
- Small Ballmoss - Tillandsia Recurvata (L.) L.
- Small Beggarticks - Bidens Discoidea (Torr. & A. Gray) Britton
- Small Black Blueberry - Vaccinium Tenellum Aiton
- Small Blacktip Ragwort - Senecio Lugens Richardson
- Small Bluebells - Mertensia Longiflora Greene
- Small Bonny Bellflower - Campanula Divaricata Michx.
- Small Bugloss - Anchusa Arvensis (L.) M. Bieb.
- Small Bur-reed - Sparganium Natans L.
- Small Burnet - Sanguisorba Minor Scop.
- Small Burnet - Sanguisorba Minor Scop. ssp. balearica (Bourg. ex Nyman) M. Garm. & C. Navarro
- Small Butterwort - Pinguicula Pumila Michx.
- Small Camas - Camassia Quamash (Pursh) Greene
- Small Camas - Camassia Quamash (Pursh) Greene ssp. azurea (A. Heller) Gould
- Small Camas - Camassia Quamash (Pursh) Greene ssp. breviflora Gould
- Small Camas - Camassia Quamash (Pursh) Greene ssp. intermedia Gould
- Small Camas - Camassia Quamash (Pursh) Greene ssp. linearis Gould
- Small Camas - Camassia Quamash (Pursh) Greene ssp. maxima Gould
- Small Camas - Camassia Quamash (Pursh) Greene ssp. quamash
- Small Capsule Dung Moss - Splachnum Ampullaceum Hedw.
- Small Carpetgrass - Arthraxon Hispidus (Thunb.) Makino
- Small Coastal Germander - Teucrium Cubense Jacq.
- Small Coastal Germander - Teucrium Cubense Jacq. var. cubense
- Small Coastal Germander - Teucrium Cubense Jacq. var. densum Jeps.
- Small Coastal Germander - Teucrium Cubense Jacq. var. laevigatum (Vahl) Shinners
- Small Coastal Germander - Teucrium Depressum Small var. densum Jeps.
- Small Coastal Germander - Teucrium Laevigatum Vahl[excluded] var. laevigatum (Vahl) Shinners
- Small Cordgrass - Spartina Maritima (M.A. Curtis) Fernald
- Small Cranberry - Vaccinium Oxycoccos L.
- Small Daylily - Hemerocallis Minor Mill.
- Small Enchanter's Nightshade - Circaea Alpina L.
- Small Enchanter's Nightshade - Circaea Alpina L. ssp. alpina
- Small Enchanter's Nightshade - Circaea Alpina L. ssp. pacifica (Asch. & Magnus) P.H. Raven
- Small Evening Primrose - Camissonia Minor (A. Nelson) P.H. Raven
- Small Eyebright - Euphrasia Randii B.L. Rob.
- Small Fescue - Vulpia Microstachys (Nutt.) Munro
- Small Floating Mannagrass - Glyceria Borealis (Nash) Batchelder
- Small Fryxellwort - Fryxellia Pygmaea (Correll) D.M. Bates
- Small Geranium - Geranium Pusillum L.
- Small Green Wood Orchid - Platanthera Clavellata (Michx.) Luer
- Small Indian Breadroot - Pediomelum Pentaphyllum (L.) Rydb.
- Small Japanese Silver Grass - Miscanthus Oligostachyus Stapf
- Small Limestone Moss - Seligeria Bruch & Schimp.
- Small Limestone Moss - Seligeria Calcarea (Hedw.) Bruch & Schimp.
- Small Limestone Moss - Seligeria Campylopoda Kindb.
- Small Limestone Moss - Seligeria Oelandica C.E.O. Jensen & Medel.
- Small Limestone Moss - Seligeria Pusilla (Hedw.) Bruch & Schimp.
- Small Limestone Moss - Seligeria Subimmersa Lindb.
- Small Limestone Moss - Seligeria Tristichoides Kindb.
- Small Matweed - Guilleminea Densa (Humb. & Bonpl. ex Schult.) Moq.
- Small Matweed - Guilleminea Densa (Humb. & Bonpl. ex Schult.) Moq. var. aggregata Uline & Bray
- Small Matweed - Guilleminea Densa (Humb. & Bonpl. ex Schult.) Moq. var. densa
- Small Mountain Bittercress - Cardamine Clematitis Shuttlw. ex A. Gray
- Small Onion - Allium Parvum Kellogg
- Small Palafox - Palafoxia Callosa (Nutt.) Torr. & A. Gray
- Small Penstemon - Penstemon Attenuatus Douglas ex Lindl. var. pseudoprocerus (Rydb.) Cronquist
- Small Phacelia - Phacelia Minutissima L.F. Hend.
- Small Philippine Acacia - Acacia Confusa Merr.
- Small Pondweed - Potamogeton Pusillus L.
- Small Pondweed - Potamogeton Pusillus L. ssp. gemmiparus (J.W. Robbins) Haynes & C.B. Hellquist
- Small Pondweed - Potamogeton Pusillus L. ssp. pusillus
- Small Pondweed - Potamogeton Pusillus L. ssp. tenuissimus (Mert. & W.D.J. Koch) Haynes & C.B. Hellquis
- Small Povertyweed - Monolepis Pusilla Torr. ex S. Watson
- Small Prescott Orchid - Prescotia Oligantha (Sw.) Lindl.
- Small Pussytoes - Antennaria Howellii Greene ssp. petaloidea (Fernald) Bayer
- Small Redleaf - Schizachyrium Fragile (R. Br.) A. Camus
- Small Rocklettuce - Pinaropappus Parvus S.F. Blake
- Small Saltbush - Atriplex Eardleyae Aellen
- Small Saxifrage - Saxifraga Adscendens L. ssp. oregonensis (Raf.) Bacig.
- Small Shell Ginger - Alpinia Mutica Roxb.
- Small Skullcap - Scutellaria Parvula Michx.
- Small Skullcap - Scutellaria Parvula Michx. var. australis Fassett
- Small Skullcap - Scutellaria Parvula Michx. var. parvula
- Small Spikerush - Eleocharis Minima Kunth
- Small Spreading Pogonia - Cleistes Bifaria (Fernald) Catling & Gregg
- Small Stilted Mangrove - Rhizophora Stylosa Griff.
- Small Tarweed - Madia Exigua (Sm.) A. Gray
- Small Treefern - Cyathea Parvula (Jenman) Domin
- Small Tumbleweed Mustard - Sisymbrium Loeselii L.
- Small Twistedstalk - Streptopus Streptopoides (Ledeb.) Frye & Rigg
- Small Twistedstalk - Streptopus Streptopoides (Ledeb.) Frye & Rigg ssp. streptopoides
- Small Twistedstalk - Streptopus Streptopoides (Ledeb.) Frye & Rigg ssp. streptopoides var. brevipes (Baker) Fa
- Small Venus' Looking-glass - Triodanis Biflora (Ruiz & Pav.) Greene
- Small Waterwort - Elatine Minima (Nutt.) Fisch. & C.A. Mey.
- Small White Clover - Trifolium Nigrescens Viv.
- Small White Violet - Viola Macloskeyi Lloyd
- Small White Violet - Viola Macloskeyi Lloyd ssp. macloskeyi
- Small Whorled Pogonia - Isotria Medeoloides (Pursh) Raf.
- Small Wirelettuce - Stephanomeria Exigua Nutt.
- Small Wirelettuce - Stephanomeria Exigua Nutt. ssp. exigua
- Small Woodland Sunflower - Helianthus Microcephalus Torr. & A. Gray
- Small Yellow Nicker - Caesalpinia Divergens Urb.
- Small's Acroporium Moss - Acroporium Smallii (R.S. Williams) H.A. Crum & L.E. Anderson
- Small's Beardtongue - Penstemon Smallii A. Heller
- Small's Blacksnakeroot - Sanicula Smallii E.P. Bicknell
- Small's Bogbutton - Lachnocaulon Minus (Chapm.) Small
- Small's Flax - Linum Carteri Small var. smallii C.M. Rogers
- Small's Goldenrod - Solidago Pinetorum Small
- Small's Hackberry - Celtis Laevigata Willd. var. smallii (Beadle) Sarg.
- Small's Jointweed - Polygonella Myriophylla (Small) Horton
- Small's Milkpea - Galactia Smallii H.J. Rogers ex Herndon
- Small's Noseburn - Tragia Smallii Shinners
- Small's Purslane - Portulaca Smallii P. Wilson
- Small's Ragwort - Packera Anonyma (Alph. Wood) W.A. Weber & Á. Löve
- Small's Rainlily - Cooperia Smallii Alexander
- Small's Redbird Flower - Pedilanthus Tithymaloides (L.) Poit. ssp. smallii (Millsp.) Dressler
- Small's Skullcap - Scutellaria Multiglandulosa (Kearney) Small ex Harper
- Small's Southern Clarkia - Clarkia Australis E. Small
- Small's Yelloweyed Grass - Xyris Smalliana Nash
- Small-flower Prairie Wallflower - Erysimum Coarctatum Fernald
- Small-flowered Calycadenia - Calycadenia Micrantha R.L. Carr & G.D. Carr
- Small-leaf Angelica - Angelica Pinnata S. Watson
- Small-leaf Arrowwood - Viburnum Obovatum Walter
- Small-leaf Bentgrass - Agrostis Microphylla Steud.
- Small-leaf Bittercress - Cardamine Microphylla M.F. Adams
- Small-leaf Bittercress - Cardamine Microphylla M.F. Adams ssp. blaisdellii (Eastw.) D.F. Murray & S. Kelso
- Small-leaf Bittercress - Cardamine Microphylla M.F. Adams ssp. microphylla
- Small-leaf Bur Cucumber - Sicyos Microphyllus Kunth
- Small-leaf Climbing Fern - Lygodium Microphyllum (Cav.) R. Br.
- Small-leaf Delissea - Delissea Lauliiana Lammers
- Small-leaf False Cloak Fern - Argyrochosma Microphylla (Mett. ex Kuhn) Windham
- Small-leaf Fiddleleaf - Nama Parvifolium (Torr.) Greenm.
- Small-leaf Geigertree - Cordia Parvifolia A. DC.
- Small-leaf Globemallow - Sphaeralcea Parvifolia A. Nelson
- Small-leaf Manzanita - Arctostaphylos ×parvifolia Howell (pro sp.)
- Small-leaf Milkpea - Galactia Parvifolia A. Rich.
- Small-leaf Pussytoes - Antennaria Parvifolia Nutt.
- Small-leaf Pygmyweed - Crassula Drummondii (Torr. & A. Gray) Fedde
- Small-leaf Snoutbean - Rhynchosia Parvifolia DC.
- Small-leaf Spiderwort - Tradescantia Fluminensis Vell.
- Small-leaf Squarestem - Melanthera Parvifolia Small
- Small-leaved Rockdaisy - Perityle Megalocephala (S. Watson) J.F. Macbr. var. oligophylla A. Powell
- Small-lobe Navarretia - Navarretia Hamata Greene ssp. parviloba Day
- Smallanthus - Smallanthus Mack. ex Small
- Smallawned Sedge - Carex Microchaeta T. Holm
- Smallawned Sedge - Carex Microchaeta T. Holm ssp. microchaeta
- Smallbract Sedge - Carex Subbracteata Mack.
- Smallbristle Hound's Tongue - Cynoglossum Microglochin Benth.
- Smallcane - Lasiacis (griseb.) Hitchc.
- Smallcane - Lasiacis Divaricata (L.) Hitchc.
- Smallflower Aiea - Nothocestrum Breviflorum A. Gray
- Smallflower Baby Blue Eyes - Nemophila Aphylla (L.) Brummitt
- Smallflower Beach Pea - Lathyrus Japonicus Willd. var. parviflorus Fassett
- Smallflower Bird's-foot Trefoil - Lotus Parviflorus Desf.
- Smallflower Blueberry - Vaccinium Virgatum Aiton
- Smallflower Bluecurls - Trichostema Micranthum A. Gray
- Smallflower Bruguiera - Bruguiera Parviflora (Roxb.) Wight & Arn. ex Griffith
- Smallflower Bur Cucumber - Sicyos Parviflorus Willd.
- Smallflower Buttercup - Ranunculus Parviflorus L.
- Smallflower Century Plant - Agave Parviflora Torr.
- Smallflower Chastetree - Vitex Parviflora Juss.
- Smallflower Clermontia - Clermontia Parviflora Gaudich. ex A. Gray
- Smallflower Columbine - Aquilegia Brevistyla Hook.
- Smallflower Creepingoxeye - Wedelia Parviflora Rich.
- Smallflower Deathcamas - Zigadenus Micranthus Eastw.
- Smallflower Deathcamas - Zigadenus Micranthus Eastw. var. fontanus (Eastw.) O.S. Walsh ex McNeal
- Smallflower Deathcamas - Zigadenus Micranthus Eastw. var. micranthus
- Smallflower Delissea - Delissea Parviflora Hillebr.
- Smallflower Desert-chicory - Pyrrhopappus Pauciflorus (D. Don) DC.
- Smallflower Dwarf-flax - Hesperolinon Micranthum (A. Gray) Small
- Smallflower Fairypoppy - Meconella Denticulata Greene
- Smallflower False Foxglove - Agalinis Paupercula (A. Gray) Britton
- Smallflower False Foxglove - Agalinis Paupercula (A. Gray) Britton var. borealis Pennell
- Smallflower False Foxglove - Agalinis Paupercula (A. Gray) Britton var. paupercula
- Smallflower Fescue - Festuca Minutiflora Rydb.
- Smallflower Fishhook Cactus - Sclerocactus Parviflorus Clover & Jotter
- Smallflower Fishhook Cactus - Sclerocactus Parviflorus Clover & Jotter ssp. havasupaiensis (Clover) F. Hochstätter
- Smallflower Fishhook Cactus - Sclerocactus Parviflorus Clover & Jotter ssp. parviflorus
- Smallflower Fumewort - Corydalis Micrantha (Engelm. ex A. Gray) A. Gray
- Smallflower Fumewort - Corydalis Micrantha (Engelm. ex A. Gray) A. Gray ssp. australis (Chapm.) G.B. Ownbey
- Smallflower Fumewort - Corydalis Micrantha (Engelm. ex A. Gray) A. Gray ssp. micrantha
- Smallflower Grass Of Parnassus - Parnassia Palustris L. var. parviflora (DC.) B. Boivin
- Smallflower Groundcherry - Physalis Cinerascens (Dunal) Hitchc.
- Smallflower Groundcherry - Physalis Cinerascens (Dunal) Hitchc. var. cinerascens
- Smallflower Groundcherry - Physalis Cinerascens (Dunal) Hitchc. var. spathulifolia (Torr.) J.R. Sullivan
- Smallflower Gymnosteris - Gymnosteris Parvula A. Heller
- Smallflower Hairy Willowherb - Epilobium Parviflorum Schreb.
- Smallflower Halfchaff Sedge - Lipocarpha Micrantha (Vahl) G. Tucker
- Smallflower Hawksbeard - Crepis Pulchra L.
- Smallflower Horkelia - Horkelia Fusca Lindl. ssp. parviflora (Nutt. ex Torr. & A. Gray) D.D. Keck
- Smallflower Indian Paintbrush - Castilleja Parviflora Bong. var. albida (Pennell) Ownbey
- Smallflower Indian Paintbrush - Castilleja Parviflora Bong. var. parviflora
- Smallflower Indigo - Indigofera Parviflora K. Heyne ex Wight & Arn., nom. inq.
- Smallflower Indigoberry - Randia Parvifolia Lam.
- Smallflower Lilythorn - Catesbaea Parviflora Sw.
- Smallflower Lousewort - Pedicularis Parviflora Sm. ex Rees
- Smallflower Lousewort - Pedicularis Parviflora Sm. ex Rees ssp. parviflora
- Smallflower Lovegrass - Eragrostis Parviflora (R. Br.) Trin.
- Smallflower Lupine - Lupinus Polycarpus Greene
- Smallflower Melicgrass - Melica Imperfecta Trin.
- Smallflower Milkvine - Matelea Parviflora (Torr.) Woodson
- Smallflower Milkwort - Polygala Nudata Brandegee
- Smallflower Miterwort - Mitella Stauropetala Piper
- Smallflower Miterwort - Mitella Stauropetala Piper var. stauropetala
- Smallflower Mock Buckthorn - Sageretia Minutiflora (Michx.) C. Mohr
- Smallflower Monkeyflower - Mimulus Inconspicuus A. Gray
- Smallflower Nemophila - Nemophila Parviflora Douglas ex Benth.
- Smallflower Nemophila - Nemophila Parviflora Douglas ex Benth. var. austiniae (Eastw.) Brand
- Smallflower Nemophila - Nemophila Parviflora Douglas ex Benth. var. parviflora
- Smallflower Nemophila - Nemophila Parviflora Douglas ex Benth. var. quercifolia (Eastw.) Chandler
- Smallflower Oxtongue - Picris Pauciflora Willd.
- Smallflower Panicgrass - Panicum Parvifolium Lam.
- Smallflower Pawpaw - Asimina Parviflora (Michx.) Dunal
- Smallflower Phacelia - Phacelia Dubia (L.) Trel.
- Smallflower Phacelia - Phacelia Dubia (L.) Trel. var. dubia
- Smallflower Phacelia - Phacelia Dubia (L.) Trel. var. georgiana McVaugh
- Smallflower Phreatia - Phreatia Micrantha (A. Rich.) Schltr.
- Smallflower Phyllostegia - Phyllostegia Parviflora (Gaudich.) Benth.
- Smallflower Phyllostegia - Phyllostegia Parviflora (Gaudich.) Benth. var. glabriuscula A. Gray
- Smallflower Phyllostegia - Phyllostegia Parviflora (Gaudich.) Benth. var. lydgatei (Sherff) W.L. Wagner
- Smallflower Phyllostegia - Phyllostegia Parviflora (Gaudich.) Benth. var. parviflora
- Smallflower Sandverbena - Tripterocalyx Micranthus (Torr.) Hook.
- Smallflower Soap Plant - Chlorogalum Parviflorum S. Watson
- Smallflower Starviolet - Stenaria Rupicola (Greenm.) Terrell
- Smallflower Swallow-wort - Cynanchum Parviflorum Sw.
- Smallflower Sweetbrier - Rosa Micrantha Borrer ex Sm.
- Smallflower Tamarisk - Tamarix Parviflora DC.
- Smallflower Tansyaster - Machaeranthera Parviflora A. Gray
- Smallflower Thoroughwort - Eupatorium Semiserratum DC.
- Smallflower Threadplant - Nemacladus Ramosissimus Nutt.
- Smallflower Touchmenot - Impatiens Parviflora DC.
- Smallflower Wakerobin - Trillium Albidum J.D. Freeman ssp. parviflorum (Soukup) K.L. Chambers & S.C. Meye
- Smallflower Western Rosinweed - Calycadenia Pauciflora A. Gray
- Smallflower Woodland-star - Lithophragma Parviflorum (Hook.) Nutt. ex Torr. & A. Gray
- Smallflower Woodland-star - Lithophragma Parviflorum (Hook.) Nutt. ex Torr. & A. Gray var. parviflorum
- Smallflower Wrightwort - Carlowrightia Parviflora (Buckley) Wassh.
- Smallflowered Anemone - Anemone Parviflora Michx.
- Smallflowered Anemone - Anemone Parviflora Michx. var. grandiflora Ulbr.
- Smallflowered Anemone - Anemone Parviflora Michx. var. parviflora
- Smallflowered Milkvetch - Astragalus Nuttallianus DC.
- Smallflowered Milkvetch - Astragalus Nuttallianus DC. var. austrinus (Small) Barneby
- Smallflowered Milkvetch - Astragalus Nuttallianus DC. var. nuttallianus
- Smallflowered Woodrush - Luzula Fastigiata E. Mey.
- Smallflowered Woodrush - Luzula Parviflora (Ehrh.) Desv.
- Smallfruit Agrimony - Agrimonia Microcarpa Wallr.
- Smallfruit Beggarticks - Bidens Mitis (Michx.) Sherff
- Smallfruit Primrose-willow - Ludwigia Microcarpa Michx.
- Smallfruit Spikerush - Eleocharis Microcarpa Torr.
- Smallgrass - Microchloa R. Br.
- Smallhead Arnica - Arnica Gracilis Rydb.
- Smallhead Aster - Symphyotrichum Parviceps (Burgess) G.L. Nesom
- Smallhead Beaksedge - Rhynchospora Microcephala (Britton) Britton
- Smallhead Blazing Star - Liatris Microcephala (Small) K. Schum.
- Smallhead Cat's Ear - Hypochaeris Microcephala (Sch. Bip.) Cabrera
- Smallhead Cat's Ear - Hypochaeris Microcephala (Sch. Bip.) Cabrera var. albiflora (Kuntze) Cabrera
- Smallhead Cat's Ear - Hypochaeris Microcephala (Sch. Bip.) Cabrera var. microcephala (Sch. Bip.) Cabrera [exclu
- Smallhead Clover - Trifolium Microcephalum Pursh
- Smallhead Doll's Daisy - Boltonia Diffusa Elliott
- Smallhead Doll's Daisy - Boltonia Diffusa Elliott var. diffusa
- Smallhead Doll's Daisy - Boltonia Diffusa Elliott var. interior Fernald & Grisc.
- Smallhead Goldenweed - Pyrrocoma Liatriformis Greene
- Smallhead Heathgoldenrod - Tonestus Microcephalus (Cronquist) G.L. Nesom & D. Morgan
- Smallhead Pipewort - Eriocaulon Microcephalum Kunth
- Smallhead Rush - Juncus Brachycephalus (Engelm.) Buchenau
- Smallhead Sneezeweed - Helenium Microcephalum DC.
- Smallhead Sneezeweed - Helenium Microcephalum DC. var. microcephalum
- Smallhead Sneezeweed - Helenium Microcephalum DC. var. ooclinium (A. Gray) Bierner
- Smallhead Star-thistle - Centaurea Calcitrapoides L.
- Smallhead Tetramolopium - Tetramolopium Conyzoides (A. Gray) Hillebr.
- Smallheaded Townsend Daisy - Townsendia Microcephala Dorn
- Smallleaf Giant Hyssop - Agastache Parvifolia Eastw.
- Smallleaf Phyllopsora Lichen - Phyllopsora Parvifolia (Pers.) Müll. Arg.
- Smallleaf Shield Lichen - Heterodermia Microphylla (Kurok.) Skorepa
- Smallnut Fimbry - Fimbristylis Microcarya F. Muell. var. tainanensis (Ohwi) H.Y. Liu
- Smallpetal Cinquefoil - Potentilla Glandulosa Lindl. ssp. micropetala (Rydb.) D.D. Keck
- Smallray Goldfields - Lasthenia Microglossa (DC.) Greene
- Smallray Swampwort - Enydra Sessilis (Sw.) DC.
- Smallseed Paspalum - Paspalum Parviflorum Rohde ex Flueggé
- Smallseed Pygmyweed - Crassula Longipes (Rose) Bywater & Wickens
- Smallseed Sandmat - Chamaesyce Polycarpa (Benth.) Millsp. ex Parish
- Smallspike False Nettle - Boehmeria Cylindrica (L.) Sw.
- Smallspore Map Lichen - Rhizocarpon Microsporum Lynge
- Smallstalk Necklace Fern - Lindsaea Stricta (Sw.) Dryand. ex Sm.
- Smallstalk Necklace Fern - Lindsaea Stricta (Sw.) Dryand. ex Sm. var. jamesoniiformis Kramer
- Smallstamen Viper's Bugloss - Echium Coincyanum Lacaita [excluded]
- Smallwing Sedge - Carex Microptera Mack.
- Smartweed Dodder - Cuscuta Polygonorum Engelm.
- Smartweed Leaf-flower - Phyllanthus Polygonoides Nutt. ex Spreng.
- Smartweed - Polygonum Kawagoeanum Makino
- Smelly Wallflower - Erysimum Odoratum Ehrh.
- Smelowskia Borealis (Greene) Drury & Rollins ssp. jordalii (Drury & Rollins) Cody
- Smelowskia Calycina (Stephan ex Willd.) C.A. Mey. ssp. integrifolia (Seem.) Hultén
- Smelowskia Calycina (Stephan ex Willd.) C.A. Mey. var. media Drury & Rollins
- Smelowskia Fremontii S. Watson
- Smelowskia Fremontii S. Watson var. bisulcata (Greene) O.E. Schulz
- Smelowskia Porsildii (Drury & Rollins) Yurtsev
- Smilacina Amplexicaulis Nutt.
- Smilacina Amplexicaulis Nutt. var. glabra J.F. Macbr.
- Smilacina Amplexicaulis Nutt. var. jenkinsii B. Boivin
- Smilacina Amplexicaulis Nutt. var. ovata B. Boivin
- Smilacina Borealis (Aiton) Raf. var. uniflora Menzies ex Schult. & Schult. f.
- Smilacina Ciliata Desf.
- Smilacina Flexicaulis Wender
- Smilacina Liliacea (Greene) Wynd
- Smilacina Racemosa (L.) Desf.
- Smilacina Racemosa (L.) Desf. var. amplexicaulis (Nutt.) S. Watson
- Smilacina Racemosa (L.) Desf. var. brachystyla G. Hend.
- Smilacina Racemosa (L.) Desf. var. cylindrata Fernald
- Smilacina Racemosa (L.) Desf. var. glabra (J.F. Macbr.) H. St. John
- Smilacina Racemosa (L.) Desf. var. jenkinsii (B. Boivin) B. Boivin
- Smilacina Racemosa (L.) Desf. var. lanceolata B. Boivin
- Smilacina Racemosa (L.) Desf. var. typica Fernald
- Smilacina Sessilifolia Nutt. ex Baker
- Smilacina Stellata (L.) Desf.
- Smilacina Stellata (L.) Desf. var. crassa Vict.
- Smilacina Stellata (L.) Desf. var. mollis Farw.
- Smilacina Stellata (L.) Desf. var. sessilifolia (Nutt. ex Baker) G. Hend.
- Smilacina Stellata (L.) Desf. var. sylvatica Vict. & J. Rousseau
- Smilacina Trifolia (L.) Desf.
- Smilax Bona-nox L. var. exauriculata Fernald
- Smilax Bona-nox L. var. hastata (Willd.) A. DC.
- Smilax Bona-nox L. var. hederifolia (Bey.) Fernald
- Smilax Domingensis auct. non Willd.
- Smilax Ecirrhata (Engelm. ex Kunth) S. Watson var. biltmoreana (Small) H.E. Ahles
- Smilax Ecirrhata (Engelm. ex Kunth) S. Watson var. hugeri (Small) H.E. Ahles
- Smilax Glauca Walter var. genuina S.F. Blake
- Smilax Glauca Walter var. leurophylla S.F. Blake
- Smilax Havanensis auct. non Jacq.
- Smilax Herbacea L. var. lasioneura (Hook.) A. DC.
- Smilax Herbacea L. var. pulverulenta (Michx.) A. Gray
- Smilax Hispida Muhl. ex Torr.
- Smilax Hispida Muhl. ex Torr. var. australis Small
- Smilax Hispida Muhl. ex Torr. var. montana Coker
- Smilax Humilis Mill., nom. utique rej.
- Smilax Lanceolata auct. non L.
- Smilax Leptanthera Pennell
- Smilax Megacarpa Morong
- Smilax Melastomifolia Sm. var. subinermis Hillebr.
- Smilax Rotundifolia L. var. crenulata Small & A. Heller
- Smilax Rotundifolia L. var. quadrangularis (Muhl. ex Willd.) Alph. Wood
- Smilax Sandwicensis Kunth
- Smilax Sandwicensis Kunth var. crassifolia Hillebr.
- Smilax Tamnifolia Michx.
- Smilax Tamnoides L. var. hispida (Muhl. ex Torr.) Fernald
- Smilograss - Piptatherum Miliaceum (L.) Coss.
- Smith's Buckthorn - Rhamnus Smithii Greene
- Smith's Bulrush - Schoenoplectiella Smithii (A. Gray) Hayas.
- Smith's Draba - Draba Smithii Gilg ex O.E. Schulz
- Smith's Eucalyptus - Eucalyptus Smithii R.T. Baker
- Smith's Hygrohypnum Moss - Hygrohypnum Smithii (Sw. Broth.
- Smith's Leptodon Moss - Leptodon Smithii (Hedw.) F. Weber & D. Mohr
- Smith's Melicgrass - Melica Smithii (Porter ex A. Gray) Vasey
- Smith's Mint - Mentha ×smithiana Graham
- Smith's Sunflower - Helianthus Smithii Heiser
- Smith's Tonguefern - Elaphoglossum Smithii (Baker) Christ
- Smithfield Blackberry - Rubus Pernagaeus Fernald
- Smithton Peppermint Gum - Eucalyptus Nitida Hook. f.
- Smokebush - Buddleja Madagascariensis Lam.
- Smoketree - Cotinus Mill.
- Smoketree - Psorothamnus Spinosus (A. Gray) Barneby
- Smokey Mariposa - Calochortus Leichtlinii Hook. f.
- Smoooth Thorn-apple - Datura Inermis Jacq. [excluded]
- Smooth Alkaligrass - Puccinellia Sublaevis (Holmb.) Tzvelev
- Smooth Arizona Cypress - Hesperocyparis Glabra (Sudw.) Bartel
- Smooth Aster - Eucephalus Glabratus (Greene) Greene
- Smooth Ayenia - Ayenia Glabra S. Watson
- Smooth Azalea - Rhododendron Arborescens (Pursh) Torr.
- Smooth Babybonnets - Coursetia Glabella (A. Gray) Lavin
- Smooth Baccharis - Baccharis Plummerae A. Gray ssp. glabrata Hoover
- Smooth Barley - Hordeum Murinum L. ssp. glaucum (Steud.) Tzvelev
- Smooth Bedstraw - Cruciata Laevipes Opiz
- Smooth Beggartick - Bidens Laevis (L.) Britton, Sterns & Poggenb.
- Smooth Black Sedge - Carex Nigra (L.) Reichard
- Smooth Blackberry - Rubus Canadensis L.
- Smooth Blue Aster - Symphyotrichum Laeve (L.) Á. Löve & D. Löve
- Smooth Blue Aster - Symphyotrichum Laeve (L.) Á. Löve & D. Löve var. concinnum (Willd.) G.L. Nesom
- Smooth Blue Aster - Symphyotrichum Laeve (L.) Á. Löve & D. Löve var. laeve
- Smooth Blue Aster - Symphyotrichum Laeve (L.) Á. Löve & D. Löve var. purpuratum (Nees) G.L. Nesom
- Smooth Bogrush - Schoenus Apogon Roem. & Schult.
- Smooth Brome - Bromus Inermis Leyss.
- Smooth Brome - Bromus Inermis Leyss. ssp. inermis
- Smooth Brome - Bromus Inermis Leyss. ssp. inermis var. divaricatus Rohlena
- Smooth Brome - Bromus Inermis Leyss. ssp. inermis var. inermis
- Smooth Browntop - Microstegium Glabratum (Brongn.) A. Camus
- Smooth Bur Cucumber - Sicyos Glaber Wooton
- Smooth Carrionflower - Smilax Herbacea L.
- Smooth Cat's Ear - Hypochaeris Glabra L.
- Smooth Chastetree - Vitex Glabrata R. Br.
- Smooth Cliffbrake - Pellaea Glabella Mett. ex Kuhn
- Smooth Cliffbrake - Pellaea Glabella Mett. ex Kuhn ssp. glabella
- Smooth Cliffbrake - Pellaea Glabella Mett. ex Kuhn ssp. simplex (Butters) Á. Löve & D. Löve
- Smooth Cordgrass - Spartina Alterniflora Loisel.
- Smooth Crabgrass - Digitaria Ischaemum (Schreb.) Schreb. ex Muhl.
- Smooth Cryptantha - Cryptantha Semiglabra Barneby
- Smooth Cyanea - Cyanea Glabra (E. Wimm.) H. St. John
- Smooth Desertdandelion - Malacothrix Glabrata (A. Gray ex D.C. Eaton) A. Gray
- Smooth Devil's-claws - Pisonia Rotundata Griseb.
- Smooth Draba - Draba Glabella Pursh
- Smooth Draba - Draba Glabella Pursh var. glabella
- Smooth Dubautia - Dubautia Laevigata A. Gray
- Smooth Dwarf Polypody - Grammitis Mollissima (Fée) Proctor
- Smooth Elephantsfoot - Elephantopus Nudatus A. Gray
- Smooth False Buttonweed - Spermacoce Glabra Michx.
- Smooth False Indigo - Amorpha Laevigata Nutt.
- Smooth Fanpetals - Sida Glabra Mill.
- Smooth Filmy Fern - Hymenophyllum Polyanthos (Sw.) Sw.
- Smooth Flatsedge - Cyperus Laevigatus L.
- Smooth Forked Nailwort - Paronychia Canadensis (L.) Alph. Wood
- Smooth Four O'clock - Mirabilis Glabra (S. Watson) Standl.
- Smooth Goldfields - Lasthenia Glaberrima DC.
- Smooth Goosefoot - Chenopodium Subglabrum (S. Watson) A. Nelson
- Smooth Hawksbeard - Crepis Capillaris (L.) Wallr.
- Smooth Hawkweed - Hieracium Laevigatum Willd.
- Smooth Hawthorn - Crataegus Laevigata (Poir.) DC.
- Smooth Hedgenettle - Stachys Tenuifolia Willd.
- Smooth Honeytree - Casearia Nitida Jacq.
- Smooth Horsetail - Equisetum Laevigatum A. Braun
- Smooth Jewelflower - Streptanthus Hyacinthoides Hook.
- Smooth Johnnyberry - Miconia Laevigata (L.) D. Don
- Smooth Jointtail Grass - Mnesithea Laevis (Retz.) Kunth
- Smooth Jointtail Grass - Mnesithea Laevis (Retz.) Kunth var. laevis
- Smooth Joyweed - Alternanthera Paronychioides A. St.-Hil.
- Smooth Joyweed - Alternanthera Paronychioides A. St.-Hil. var. amazonica Huber
- Smooth Joyweed - Alternanthera Paronychioides A. St.-Hil. var. paronychioides
- Smooth Lady's Mantle - Alchemilla Glabra Neyngenfind
- Smooth Larkspur - Delphinium Glaucescens Rydb.
- Smooth Leechbush - Dendropemon Purpureus (L.) Krug & Urb.
- Smooth Lessingia - Lessingia Micradenia Greene var. glabrata (D.D. Keck) Ferris
- Smooth Loco Milkvetch - Astragalus Curvicarpus (A. Heller) J.F. Macbr. var. subglaber (Rydb.) Barneby
- Smooth Manjack - Cordia Laevigata Lam.
- Smooth Melanelia Lichen - Melanelia Glabra (Schaerer) Essl.
- Smooth Mesquite - Prosopis Laevigata (Humb. & Bonpl. ex Willd.) M.C. Johnst.
- Smooth Mountain Mahogany - Cercocarpus Montanus Raf. var. minutiflorus (Abrams) F.L. Martin
- Smooth Northern-rockcress - Braya Glabella Richardson
- Smooth Northern-rockcress - Braya Glabella Richardson ssp. glabella
- Smooth Northern-rockcress - Braya Glabella Richardson ssp. prostrata J.G. Harris
- Smooth Northern-rockcress - Braya Glabella Richardson ssp. purpurascens (R. Br.) Cody
- Smooth Oxeye - Heliopsis Helianthoides (L.) Sweet
- Smooth Oxeye - Heliopsis Helianthoides (L.) Sweet var. gracilis (Nutt.) Gandhi & R.D. Thomas
- Smooth Oxeye - Heliopsis Helianthoides (L.) Sweet var. helianthoides
- Smooth Oxeye - Heliopsis Helianthoides (L.) Sweet var. occidentalis (T.R. Fisher) Steyerm.
- Smooth Oxeye - Heliopsis Helianthoides (L.) Sweet var. scabra (Dunal) Fernald
- Smooth Penstemon - Penstemon Subglaber Rydb.
- Smooth Phacelia - Phacelia Glabra Nutt.
- Smooth Phlox - Phlox Glaberrima L.
- Smooth Phlox - Phlox Glaberrima L. ssp. glaberrima
- Smooth Phlox - Phlox Glaberrima L. ssp. interior (Wherry) Wherry
- Smooth Phlox - Phlox Glaberrima L. ssp. triflora (Michx.) Wherry
- Smooth Potato Fern - Eupodium Laeve (Sm.) Murdock
- Smooth Prickly Phlox - Linanthus Glabrum (R. Patt. & Yoder-Will.) J.M. Porter & L.A. Johnson
- Smooth Pricklypoppy - Argemone Glauca (Nutt. ex Prain) Pope
- Smooth Pricklypoppy - Argemone Glauca (Nutt. ex Prain) Pope var. decipiens G.B. Ownbey
- Smooth Pricklypoppy - Argemone Glauca (Nutt. ex Prain) Pope var. glauca
- Smooth Purple Coneflower - Echinacea Laevigata (C.L. Boynt. & Beadle) S.F. Blake
- Smooth Rattlebox - Crotalaria Pallida Aiton
- Smooth Rattlebox - Crotalaria Pallida Aiton var. obovata (G. Don) Polhill
- Smooth Rock Skullcap - Scutellaria Saxatilis Riddell
- Smooth Rockcress - Arabis Laevigata (Muhl. ex Willd.) Poir.
- Smooth Rockcress - Arabis Laevigata (Muhl. ex Willd.) Poir. var. laevigata
- Smooth Rodwood - Eugenia Glabrata (Sw.) DC.
- Smooth Rose - Rosa Blanda Aiton
- Smooth Rose - Rosa Blanda Aiton var. blanda
- Smooth Rose - Rosa Blanda Aiton var. glabra Crép.
- Smooth Rupturewort - Herniaria Glabra L.
- Smooth Saltbush - Atriplex Pusilla (Torr. ex S. Watson) S. Watson
- Smooth Sawgrass - Cladium Mariscoides (Muhl.) Torr.
- Smooth Senna - Senna Sulfurea (DC. ex Collad.) Irwin & Barneby
- Smooth Shadow Witch - Ponthieva Ventricosa (Griseb.) Fawc. & Rendle
- Smooth Small-leaf Ticktrefoil - Desmodium Marilandicum (L.) DC.
- Smooth Solomon's Seal - Polygonatum Biflorum (Walter) Elliott
- Smooth Solomon's Seal - Polygonatum Biflorum (Walter) Elliott var. biflorum (Walter) Elliott [excluded]
- Smooth Solomon's Seal - Polygonatum Biflorum (Walter) Elliott var. commutatum (Schult. & Schult. f.) Morong
- Smooth Solomon's Seal - Polygonatum Biflorum (Walter) Elliott var. hebetifolium R.R. Gates
- Smooth Solomon's Seal - Polygonatum Biflorum (Walter) Elliott var. melleum (Farw.) R. Ownbey
- Smooth Solomon's Seal - Polygonatum Biflorum (Walter) Elliott var. necopinum R. Ownbey
- Smooth Spike-primrose - Epilobium Pygmaeum (Speg.) Hoch & P.H. Raven
- Smooth Spreading Four O'clock - Mirabilis Oxybaphoides (A. Gray) A. Gray
- Smooth Strongbark - Bourreria Cassinifolia (A. Rich.) Griseb.
- Smooth Sumac - Rhus Glabra L.
- Smooth Sunflower - Helianthus Laevigatus Torr. & A. Gray
- Smooth Teatree - Leptospermum Glabrescens Wakef.
- Smooth Threadleaf Ragwort - Senecio Flaccidus Less. var. monoensis (Greene) B.L. Turner & T.M. Barkley
- Smooth Ticktrefoil - Desmodium Laevigatum (Nutt.) DC.
- Smooth Tidytips - Layia Chrysanthemoides (DC.) A. Gray
- Smooth Tofieldia - Tofieldia Glabra Nutt.
- Smooth Townsend Daisy - Townsendia Formosa Greene
- Smooth Violet Prairie Aster - Symphyotrichum Turbinellum (Lindl.) G.L. Nesom
- Smooth White Aster - Symphyotrichum Porteri (A. Gray) G.L. Nesom
- Smooth White Oldfield Aster - Symphyotrichum Racemosum (Elliott) G.L. Nesom
- Smooth White Violet - Viola Macloskeyi Lloyd ssp. pallens (Banks ex Ging) M.S. Baker
- Smooth Winterberry - Ilex Laevigata (Pursh) A. Gray
- Smooth Woodrush - Luzula Glabrata (Hoppe ex Rostk.) Desv.
- Smooth Woodsia - Woodsia Glabella R. Br. ex Richardson
- Smooth Woodyaster - Xylorhiza Glabriuscula Nutt.
- Smooth Woodyaster - Xylorhiza Glabriuscula Nutt. var. glabriuscula
- Smooth Woodyaster - Xylorhiza Glabriuscula Nutt. var. linearifolia T.J. Watson
- Smooth Yellow False Foxglove - Aureolaria Flava (L.) Farw.
- Smooth Yellow False Foxglove - Aureolaria Flava (L.) Farw. var. flava
- Smooth Yellow False Foxglove - Aureolaria Flava (L.) Farw. var. macrantha Pennell
- Smooth Yellow Nicker - Caesalpinia Culebrae (Britton & P. Wilson) Alain
- Smooth Yellow Vetch - Vicia Lutea L.
- Smooth-seed Pygmyweed - Crassula Solieri (Gay) F. Meigen
- Smoothbark St. Johnswort - Hypericum Lissophloeus P. Adams
- Smoothbeak Sedge - Carex Integra Mack.
- Smoothcone Sedge - Carex Laeviconica Dewey
- Smoothflower Lousewort - Pedicularis Bracteosa Benth. var. siifolia (Rydb.) Cronquist
- Smoothfruit Chewstick - Gouania Meyenii Steud.
- Smoothleaf Beardtongue - Penstemon Leiophyllus Pennell
- Smoothleaf Beardtongue - Penstemon Leiophyllus Pennell var. francisci-pennellii (Crosswh.) N.H. Holmgren
- Smoothleaf Beardtongue - Penstemon Leiophyllus Pennell var. leiophyllus
- Smoothpod Hoarypea - Tephrosia Leiocarpa A. Gray
- Smoothsheath Sedge - Carex Laevivaginata (Kük.) Mack.
- Smoothstem Blazingstar - Mentzelia Laevicaulis (Hook.) Torr. & A. Gray
- Smoothstem Blazingstar - Mentzelia Laevicaulis (Hook.) Torr. & A. Gray var. laevicaulis
- Smoothstem Blazingstar - Mentzelia Laevicaulis (Hook.) Torr. & A. Gray var. parviflora (Douglas ex Hook.) C.L.
- Smoothstem Sedge - Carex Laeviculmis Meinsh.
- Smooththroat Stoneseed - Lithospermum Cobrense Greene
- Smotherweed - Bassia All.
- Smut Grass - Sporobolus Indicus (L.) R. Br.
- Smut Grass - Sporobolus Indicus (L.) R. Br. var. indicus
- Smut Grass - Sporobolus Indicus (L.) R. Br. var. major (Buse) Baaijens
- Smyrnium - Smyrnium L.
- Smythea Lanceata (Tul.) Summerhayes
- Smythea Seem.
- Snail Medick - Medicago Scutellata (L.) Mill.
- Snail Orchid - Comparettia Falcata Poepp. & Endl.
- Snailfern - Cochlidium Kaulf.
- Snailflower - Vigna Caracalla (L.) Verdc. [excluded]
- Snailseed - Cocculus Diversifolius DC.
- Snailseed Pondweed - Potamogeton Bicupulatus Fernald
- Snailwood - Conostegia D. Don
- Snake Canyon Milkvetch - Astragalus Vallaris M.E. Jones
- Snake Milkvetch - Astragalus Iodanthus S. Watson var. diaphanoides Barneby
- Snake Range Bladderpod - Lesquerella Pendula Rollins
- Snake Range Buckwheat - Eriogonum Holmgrenii Reveal
- Snake River Cryptantha - Cryptantha Spiculifera (Piper) Payson
- Snake River Milkvetch - Astragalus Purshii Douglas ex Hook. var. ophiogenes (Barneby) Barneby
- Snake River Phlox - Phlox Colubrina Wherry & Constance
- Snake River Twinpod - Physaria Integrifolia (Rollins) Lichvar
- Snake River Twinpod - Physaria Integrifolia (Rollins) Lichvar var. integrifolia
- Snake River Twinpod - Physaria Integrifolia (Rollins) Lichvar var. monticola Lichvar
- Snake River Wheatgrass - Elymus Wawawaiensis J. Carlson & Barkworth
- Snake's Head - Malacothrix Coulteri Harv. & A. Gray
- Snakecactus - Bergerocactus Britton & Rose
- Snakecotton - Froelichia Moench
- Snakefern - Microgramma C. Presl
- Snakegourd - Trichosanthes Anguina L.
- Snakegourd - Trichosanthes Cucumerina L.
- Snakeherb - Dyschoriste Nees
- Snakelily - Dichelostemma Kunth
- Snakelily - Dichelostemma ×venustum (Greene) Hoover (pro sp.)
- Snakemouth Orchid - Pogonia Ophioglossoides (L.) Ker Gawl.
- Snakeroot - Ageratina Spach
- Snakeweed - Gutierrezia Lag.
- Snakewood - Condalia Cav.
- Snapdragon - Antirrhinum L.
- Snapdragon Penstemon - Keckiella Antirrhinoides (Benth.) Straw
- Snapdragon Penstemon - Keckiella Antirrhinoides (Benth.) Straw ssp. antirrhinoides
- Snapdragon Penstemon - Keckiella Antirrhinoides (Benth.) Straw ssp. microphylla (A. Gray) Straw
- Snapdragon - Sairocarpus D.a. Sutton
- Sneed's Pincushion Cactus - Escobaria Sneedii Britton & Rose
- Sneed's Pincushion Cactus - Escobaria Sneedii Britton & Rose var. leei (Rose ex Boed.) D.R. Hunt
- Sneed's Pincushion Cactus - Escobaria Sneedii Britton & Rose var. sneedii
- Sneezeweed - Achillea Ptarmica L.
- Sneezeweed - Helenium Amarum (Raf.) H. Rock
- Sneezeweed - Helenium Amarum (Raf.) H. Rock var. amarum
- Sneezeweed - Helenium Amarum (Raf.) H. Rock var. badium (A. Gray ex S. Watson) Waterf.
- Sneezeweed - Helenium L.
- Sneezeweed - Helenium ×polyphyllum Small (pro sp.)
- Snoutbean - Rhynchosia Lour.
- Snoutbean - Rhynchosia Totta (Thunb.) DC.
- Snow Arnica - Arnica Frigida C.A. Mey. ex Iljin
- Snow Arnica - Arnica Frigida C.A. Mey. ex Iljin ssp. frigida
- Snow Arnica - Arnica Frigida C.A. Mey. ex Iljin ssp. griscomii (Fernald) S.R. Downie
- Snow Buckwheat - Eriogonum Niveum Douglas ex Benth.
- Snow Buttercup - Ranunculus Nivalis L.
- Snow Cinquefoil - Potentilla Nivea L.
- Snow Cinquefoil - Potentilla Nivea L. var. nivea
- Snow Currant - Ribes Niveum Lindl.
- Snow Dwarf-primrose - Douglasia Nivalis Lindl.
- Snow Dwarf-primrose - Douglasia Nivalis Lindl. var. dentata (S. Watson) A. Gray
- Snow Dwarf-primrose - Douglasia Nivalis Lindl. var. nivalis
- Snow Gentian - Gentiana Nivalis L.
- Snow Grass - Phippsia Concinna (Th. Fr.) Lindeberg
- Snow Grass - Phippsia Concinna (Th. Fr.) Lindeberg var. algidiformis (Harry Sm.) Holmb.
- Snow Grass - Poa Sieberiana Spreng.
- Snow Gum - Eucalyptus Pauciflora Sieber ex Spreng.
- Snow In Summer - Cerastium Tomentosum L.
- Snow Indian Paintbrush - Castilleja Nivea Pennell & Ownbey
- Snow Lichen - Stereocaulon Apocalypticum Nyl.
- Snow Lichen - Stereocaulon Botryosum Ach.
- Snow Lichen - Stereocaulon Coniophyllum Lamb
- Snow Lichen - Stereocaulon Dactylophyllum Flörke
- Snow Lichen - Stereocaulon Glaucescens Tuck.
- Snow Lichen - Stereocaulon Hoffm.
- Snow Lichen - Stereocaulon Incrustatum Flörke
- Snow Lichen - Stereocaulon Leprocephalum Vain.
- Snow Lichen - Stereocaulon Microcarpum Müll. Arg.
- Snow Lichen - Stereocaulon Myriocarpum Th. Fr.
- Snow Lichen - Stereocaulon Nanodes Tuck.
- Snow Lichen - Stereocaulon Octomerum Müll. Arg.
- Snow Lichen - Stereocaulon Paschale (L.) Hoffm.
- Snow Lichen - Stereocaulon Pileatum Ach.
- Snow Lichen - Stereocaulon Rivulorum H. Magn.
- Snow Lichen - Stereocaulon Saxatile H. Magn.
- Snow Lichen - Stereocaulon Spathuliferum Vain.
- Snow Lichen - Stereocaulon Sterile (Savicz) Lamb ex Krog
- Snow Lichen - Stereocaulon Subcoralloides (Nyl.) Nyl.
- Snow Lichen - Stereocaulon Symphycheilum Lamb
- Snow Mountain Beardtongue - Penstemon Purpusii Brandegee
- Snow Mountain Buckwheat - Eriogonum Nervulosum (S. Stokes) Reveal
- Snow Mountain Willowherb - Epilobium Nivium Brandegee
- Snow On The Mountain - Euphorbia Marginata Pursh
- Snow On The Prairie - Euphorbia Bicolor Engelm. & A. Gray
- Snow Pearlwort - Sagina Nivalis (Lindbl.) Fr.
- Snow Raspberry - Rubus Nivalis Douglas ex Hook.
- Snow Squarestem - Melanthera Nivea (L.) Small
- Snow Trillium - Trillium Nivale Riddell
- Snow Willow - Salix Nivalis Hook.
- Snow-white Everlasting - Gamochaeta Chionesthes G.L. Nesom
- Snow-wreath - Neviusia A. Gray
- Snowball Cactus - Pediocactus Nigrispinus (Hochstätter) Hochstätter
- Snowball Sand Verbena - Abronia Fragrans Nutt. ex Hook.
- Snowbasin Draba - Draba Burkei (C.L. Hitchc.) Windham & Beilstein
- Snowbed Draba - Draba Crassifolia Graham
- Snowbed Sedge - Carex Rufina Drejer
- Snowbed Willow - Salix Herbacea L.
- Snowbell - Styrax L.
- Snowberry - Gaultheria L.
- Snowberry - Symphoricarpos Duham.
- Snowbrush Ceanothus - Ceanothus Velutinus Douglas ex Hook.
- Snowbrush Ceanothus - Ceanothus Velutinus Douglas ex Hook. var. velutinus
- Snowbush - Breynia Disticha J.R. Forst. & G. Forst.
- Snowdenia C.e. Hubb.
- Snowdenia Polystachya (Fresen.) Pilg.
- Snowdrop - Galanthus L.
- Snowdrop - Galanthus Nivalis L.
- Snowdrop Windflower - Anemone Sylvestris L.
- Snowflake - Leucojum L.
- Snowline Springparsley - Cymopterus Nivalis S. Watson
- Snowline Wintergreen - Pyrola Minor L.
- Snowlover - Chionophila Benth.
- Snowparsley - Cnidium Cusson ex Juss.
- Snowpeaks Raspberry - Rubus Niveus Thunb.
- Snowplant - Sarcodes Sanguinea Torr.
- Snowplant - Sarcodes Torr.
- Snowqueen - Synthyris Reniformis (Douglas ex Benth.) Benth.
- Snowqueen - Synthyris Reniformis (Douglas ex Benth.) Benth. var. cordata A. Gray
- Snowqueen - Synthyris Reniformis (Douglas ex Benth.) Benth. var. reniformis
- Snowrose - Serissa Commerson ex A. Juss.
- Snowrose - Serissa Foetida (L. f.) Lam.
- Snowy Mermaid - Libertia Formosa Graham
- Snowy Orchid - Platanthera Nivea (Nutt.) Luer
- Snowy River Wattle - Acacia Boomanii Maiden
- Snowy Thistle - Cirsium Occidentale (Nutt.) Jeps. var. candidissimum (Greene) J.F. Macbr.
- Snub Pea - Lathyrus Sulphureus W.H. Brewer ex A. Gray
- Snub Pea - Lathyrus Sulphureus W.H. Brewer ex A. Gray var. argillaceus Jeps.
- Snub Pea - Lathyrus Sulphureus W.H. Brewer ex A. Gray var. sulphureus
- Soana - Ziziphus Rignonii Delponte
- Soapbark - Quillaja Saponaria Molina
- Soapberry - Sapindus L.
- Soapbush - Clidemia Hirta (L.) D. Don
- Soapbush - Clidemia Hirta (L.) D. Don var. hirta
- Soapplant - Chlorogalum Kunth
- Soaptree Yucca - Yucca Elata (Engelm.) Engelm.
- Soapweed Yucca - Yucca Glauca Nutt.
- Soapweed Yucca - Yucca Glauca Nutt. var. glauca
- Soapwort - Saponaria L.
- Soapwort - Vaccaria Von Wolf
- Sobralia Macrantha Lindl.
- Sobralia - Sobralia Ruiz & Pav.
- Socarrillo - Dorycnium Pentaphyllum Scop.
- Socotra Dragontree - Dracaena Cinnabari Balf. f.
- Socrates Mine Jewelflower - Streptanthus Brachiatus F.W. Hoffm.
- Socrates Mine Jewelflower - Streptanthus Brachiatus F.W. Hoffm. ssp. brachiatus
- Socrates Mine Jewelflower - Streptanthus Brachiatus F.W. Hoffm. ssp. hoffmanii Dolan & LaPre
- Sodaapple Nightshade - Solanum Aculeastrum Dunal
- Sodaville Milkvetch - Astragalus Lentiginosus Douglas ex Hook. var. sesquimetralis (Rydb.) Barneby
- Soerensen's Sedge - Carex ×soerensenii Lepage
- Soft Agrimony - Agrimonia Pubescens Wallr.
- Soft Aster - Symphyotrichum Molle (Rydb.) G.L. Nesom
- Soft Beard Lichen - Usnea Fragilescens Hav. ex Lynge var. mollis (Vain.) Clerc
- Soft Bindweed - Convolvulus Pilosellifolius Desr.
- Soft Bird's-beak - Cordylanthus Mollis A. Gray
- Soft Bird's-beak - Cordylanthus Mollis A. Gray ssp. mollis
- Soft Blazingstar - Mentzelia Mollis M. Peck
- Soft Brome - Bromus Hordeaceus L.
- Soft Brome - Bromus Hordeaceus L. ssp. divaricatus (Bonnier & Layens) Kerguélen
- Soft Brome - Bromus Hordeaceus L. ssp. hordeaceus
- Soft Brome - Bromus Hordeaceus L. ssp. pseudothominii (P.M. Sm.) H. Scholz
- Soft Brome - Bromus Hordeaceus L. ssp. thominei (Hardham ex Nyman) Braun-Blanq.
- Soft Butterfly Pea - Centrosema Molle Mart. ex Benth.
- Soft Elephantsfoot - Elephantopus Mollis Kunth
- Soft Feather Pappusgrass - Enneapogon Cenchroides (Licht.) Roem. & Schult. ex C.E. Hubbard
- Soft Fissurewort - Halimolobos Mollis (Hook.) Rollins
- Soft Fox Sedge - Carex Conjuncta Boott
- Soft Globemallow - Sphaeralcea Incana Torr. ex A. Gray ssp. cuneata Kearney
- Soft Goldenaster - Chrysopsis Pilosa Nutt.
- Soft Greeneyes - Berlandiera Pumila (Michx.) Nutt.
- Soft Greeneyes - Berlandiera Pumila (Michx.) Nutt. var. pumila
- Soft Greeneyes - Berlandiera Pumila (Michx.) Nutt. var. scabrella G.L. Nesom & B.L. Turner
- Soft Heliotrope - Heliotropium Molle (Torr.) I.M. Johnst.
- Soft Lupine - Lupinus Mollis A. Heller
- Soft Milkpea - Galactia Mollis Michx.
- Soft Paspalum - Paspalum Molle Poir.
- Soft Phacelia - Phacelia Mollis J.F. Macbr.
- Soft Phlox - Phlox Mollis Wherry
- Soft Popcornflower - Plagiobothrys Mollis (A. Gray) I.M. Johnst.
- Soft Popcornflower - Plagiobothrys Mollis (A. Gray) I.M. Johnst. var. mollis
- Soft Popcornflower - Plagiobothrys Mollis (A. Gray) I.M. Johnst. var. vestitus (Greene) I.M. Johnst.
- Soft Prairie Clover - Dalea Mollissima (Rydb.) Munz
- Soft Thistle - Cirsium Carolinianum (Walter) Fernald & B.G. Schub.
- Soft Timonius - Timonius Mollis Valeton
- Soft Timonius - Timonius Mollis Valeton var. mollis
- Soft Timonius - Timonius Mollis Valeton var. submollis Fosberg & Sachet
- Soft Timonius - Timonius Mollis Valeton var. villosissimus (Kaneh.) Fosberg & Sachet
- Soft Twinevine - Funastrum Torreyi (A. Gray) Schltr.
- Soft Western Rosinweed - Calycadenia Mollis A. Gray
- Soft-hair Marbleseed - Onosmodium Bejariense DC. ex A. DC.
- Soft-hair Marbleseed - Onosmodium Bejariense DC. ex A. DC. var. bejariense
- Soft-stem Spikerush - Eleocharis Mamillata (Lindb. f.) Lindb. f.
- Softhair Coneflower - Rudbeckia Mollis Elliott
- Softhair False Pennyroyal - Hedeoma Mollis Torr.
- Softhair Marbleseed - Onosmodium Bejariense DC. ex A. DC. var. hispidissimum (Mack.) B.L. Turner
- Softhair Marbleseed - Onosmodium Bejariense DC. ex A. DC. var. subsetosum (Mack. & Bush) B.L. Turner
- Softhairy Indigo - Indigofera Pilosa Poir.
- Softhairy Maiden Fern - Thelypteris Pilosa (M. Martens & Galeotti) Crawford
- Softleaf Arrowwood - Viburnum Molle Michx.
- Softleaf Blackberry - Rubus Mollior L.H. Bailey
- Softleaf Indian Paintbrush - Castilleja Mollis Pennell
- Softleaf Mimosa - Mimosa Malacophylla A. Gray
- Softleaf Rosette Grass - Dichanthelium Malacophyllum (Nash) Gould
- Softleaf Sedge - Carex Disperma Dewey
- Softseed Wild Petunia - Ruellia Malacosperma Greenm.
- Softstem Bulrush - Schoenoplectus Tabernaemontani (C.C. Gmel.) Palla
- Soja Hispida Moench
- Soja Max (L.) Piper
- Sola Pith Plant - Aeschynomene Aspera L.
- Solander's Geranium - Geranium Solanderi Carolin
- Solandra Longiflora Tussac [excluded]
- Solandra - Solandra Sw.
- Solano False Bindweed - Calystegia Purpurata (Greene) Brummitt ssp. solanensis (Jeps.) Brummitt
- Solanoa Purpurascens (A. Gray) Greene
- Solanum Aculeatissimum sensu Schulz, non Jacq.
- Solanum Alatum Moench
- Solanum Americanum Mill. var. baylisii D'Arcy, nom. inq.
- Solanum Americanum Mill. var. nodiflorum (Jacq.) Edmonds
- Solanum Americanum Mill. var. patulum (L.) Edmonds
- Solanum Americanum auct. non Mill.
- Solanum Anguivi Lam.
- Solanum Antillarum O.E. Schulz
- Solanum Auriculatum Aiton
- Solanum Blodgettii Chapm.
- Solanum Californicum Dunal
- Solanum Capsicastrum Link ex Schauer
- Solanum Caribaeum Dunal
- Solanum Carolinense L. var. hirsutum (Nutt.) A. Gray
- Solanum Chenopodioides auct. non Lam.
- Solanum Ciliatum Lam.
- Solanum Cornutum auct. non Lam.
- Solanum Deflexum Greenm.
- Solanum Drymophilum O.E. Schulz
- Solanum Erianthum D. Don var. adulterinum (Ham. ex G. Don) Baker & Simmonds
- Solanum Ficifolium Ortega
- Solanum Fistulosum Dunal ex Poir.
- Solanum Floridanum Shuttlw. ex Dunal
- Solanum Glaucum Dunal
- Solanum Godfreyi Shinners
- Solanum Gracile Dunal, non Sendtn. 1846
- Solanum Gracile Otto
- Solanum Gracile sensu Small
- Solanum Gracilius Herter
- Solanum Guamense Merr.
- Solanum Guanicense Urb.
- Solanum Haleakalaense H. St. John
- Solanum Hermannii Dunal
- Solanum Hillebrandii H. St. John
- Solanum Houstonii Dunel 1813, non Martyn 1807
- Solanum Incompletum Dunal var. glabratum Hillebr.
- Solanum Incompletum Dunal var. mauiense Hillebr.
- Solanum Intrusum Soria
- Solanum Kavaiense Hillebr.
- Solanum Laciniatum Aiton
- Solanum Linnaeanum Hepper & P.-M. L. Jaeger
- Solanum Luteum Mill.
- Solanum Luteum Mill. ssp. alatum (Moench) Dostál
- Solanum Mariannense Hosok.
- Solanum Nelsonii Dunal var. thomasiifolium Seem.
- Solanum Nigrum L. var. americanum (Mill.) O.E. Schulz
- Solanum Nigrum L. var. douglasii (Dunal) A. Gray
- Solanum Nigrum L. var. villosum L.
- Solanum Nigrum L. var. virginicum L.
- Solanum Nigrum auct. non L.
- Solanum Nodiflorum Jacq.
- Solanum Ottonis auct. non Hyl.
- Solanum Perplexum Small
- Solanum Persicifolium Dunal
- Solanum Physalifolium Rusby var. nitidibaccatum (Bitter) Edmonds
- Solanum Pterocaulon Dunal [excluded]
- Solanum Ptychanthum Dunal, database artifact
- Solanum Puberulum Nutt. ex Seem.
- Solanum Rantonnetii Carrière
- Solanum Rubrum auct. non L.
- Solanum Sarachoides auct. non Sendtn.
- Solanum Sarrachoides auct. non Sendtn., orth. var.
- Solanum Sodomeum L., nom. utique rej.
- Solanum Sublobatum auct. non Willd. ex Roem. & Schult.
- Solanum Surattense Burm. f.
- Solanum Topiro Humb. & Bonpl. ex Dunal
- Solanum Torreyi A. Gray
- Solanum Verbascifolium L., nom. utique rej.
- Solanum Verbascifolium auct. non L.
- Solanum Villosum auct. non (L.) Mill.
- Solanum Wallacei (A. Gray) Parish ssp. clokeyi (Munz) Thorne
- Solanum Wallacei (A. Gray) Parish var. clokeyi (Munz) McMinn
- Soldier Beaksedge - Rhynchospora Tenerrima Nees ex Spreng.
- Soldier Meadows Cinquefoil - Potentilla Basaltica Tiehm & Ertter
- Soldier Rockcress - Arabis Lemmonii S. Watson var. depauperata (A. Nelson & Kennedy) Rollins
- Soldier Rockcress - Arabis Lemmonii S. Watson var. drepanoloba (Greene) Rollins
- Soldier's Orchid - Zeuxine Strateumatica (L.) Schltr.
- Soldierbush - Tournefortia L.
- Soldierwood - Colubrina Elliptica (Sw.) Briz. & Stern
- Soleirolia - Soleirolia Gaudich.
- Solenospora Hassei (Zahlbr.) Zahlbr.
- Solenospora Lichen - Solenospora A. Massal.
- Solenospora Lichen - Solenospora Candicans (Dicks.) J. Steiner
- Solenospora Lichen - Solenospora Crenata (Herre) Zahlbr.
- Solenospora Lichen - Solenospora Holophaea (Mont.) G. Sampaio
- Solenostemon - Solenostemon Thonn.
- Solidago Aestivalis E.P. Bicknell
- Solidago Altissima L. var. altissima
- Solidago Altissima L. var. canescens (A. Gray) M.C. Johnst.
- Solidago Altissima L. var. gilvocanescens (Rydb.) Semple
- Solidago Altissima L. var. pluricephala M.C. Johnst.
- Solidago Altissima L. var. procera (Aiton) Fernald
- Solidago Amplexicaulis Torr. & A. Gray ex A. Gray, non M. Martens
- Solidago Angusta Torr. & A. Gray
- Solidago Angustifolia Elliott
- Solidago Anticostensis Fernald
- Solidago Arguta Aiton ssp. boottii (Hook.) G. Morton
- Solidago Arguta Aiton ssp. caroliniana (A. Gray) G. Morton
- Solidago Arguta Aiton ssp. pseudoyadkinensis G. Morton
- Solidago Arguta Aiton var. strigosa (Small) Steyerm.
- Solidago Arizonica (A. Gray) Wooton & Standl.
- Solidago Aspera Aiton
- Solidago Asteroides Semple
- Solidago Austrina Small
- Solidago Axillaris Pursh
- Solidago Bellidifolia Greene
- Solidago Bicolor L. var. concolor Torr. & A. Gray
- Solidago Bicolor L. var. lanata (Hook.) Seymour
- Solidago Bicolor L. var. ovalis Farw.
- Solidago Bicolor L. var. tonsa (Fernald) B. Boivin
- Solidago Bigelovii A. Gray
- Solidago Bigelovii A. Gray var. wrightii (A. Gray) A. Gray
- Solidago Boottii Hook.
- Solidago Boottii Hook. var. brachyphylla (Chapm. ex Torr. & A. Gray) A. Gray
- Solidago Boottii Hook. var. caroliniana (A. Gray) Cronquist
- Solidago Boottii Hook. var. ludoviciana A. Gray
- Solidago Caesia L. var. axillaris (Pursh) A. Gray
- Solidago Caesia L. var. caesia
- Solidago Caesia L. var. curtisii (Torr. & A. Gray) Alph. Wood
- Solidago Caesia L. var. hispida Alph. Wood
- Solidago Caesia L. var. paniculata A. Gray
- Solidago Californica Nutt. var. nevadensis A. Gray
- Solidago Camporum (Greene) A. Nelson
- Solidago Canadensis L. ssp. elongata (Nutt.) D.D. Keck
- Solidago Canadensis L. ssp. salebrosa (Piper) D.D. Keck
- Solidago Canadensis L. var. arizonica A. Gray
- Solidago Canadensis L. var. bartramiana (Fernald) Beaudry
- Solidago Canadensis L. var. canescens A. Gray
- Solidago Canadensis L. var. elongata (Nutt.) M. Peck
- Solidago Canadensis L. var. rupestris (Raf.) Porter
- Solidago Canadensis L. var. scabra Torr. & A. Gray
- Solidago Canadensis L. var. subserrata (DC.) Cronquist
- Solidago Canescens (Rydb.) Friesner
- Solidago Caroliniana (L.) Britton, Sterns & Poggenb.
- Solidago Celtidifolia Small
- Solidago Chapmanii A. Gray
- Solidago Chlorolepis Fernald
- Solidago Chrysolepis Fernald
- Solidago Chrysopsis Small
- Solidago Chrysothamnoides (Greene) Bush
- Solidago Ciliosa Greene
- Solidago Conferta Mill.
- Solidago Confinis A. Gray
- Solidago Corymbosa Elliott
- Solidago Curtisii Torr. & A. Gray var. pubens (M.A. Curtis) A. Gray
- Solidago Decemflora DC.
- Solidago Decumbens Greene
- Solidago Decumbens Greene var. chlorolepis (Fernald) Beaudry
- Solidago Decumbens Greene var. oreophila (Rydb.) Fernald
- Solidago Delicatula Small
- Solidago Dispersa Small
- Solidago Drummondii Torr. & A. Gray
- Solidago Dumetorum Lunell
- Solidago Edisoniana Mack.
- Solidago Elliottii Torr. & A. Gray
- Solidago Elliottii Torr. & A. Gray var. ascendens Fernald
- Solidago Elliottii Torr. & A. Gray var. edisoniana (Mack.) Fernald
- Solidago Elliottii Torr. & A. Gray var. pedicellata Fernald
- Solidago Elliptica Aiton
- Solidago Elongata Nutt.
- Solidago Farwellii Fernald
- Solidago Flavovirens Chapm.
- Solidago Galetorum (Greene) Friesner
- Solidago Gigantea Aiton ssp. serotina (Kuntze) McNeill
- Solidago Gigantea Aiton var. leiophylla Fernald
- Solidago Gigantea Aiton var. pitcheri (Nutt.) Shinners
- Solidago Gigantea Aiton var. serotina (Kuntze) Cronquist
- Solidago Gigantea Aiton var. shinnersii Beaudry
- Solidago Gillmanii (A. Gray) Steele
- Solidago Gilvocanescens (Rydb.) Smyth
- Solidago Glaberrima M. Martens
- Solidago Glaberrima M. Martens var. moritura (Steele) Palmer & Steyerm.
- Solidago Glutinosa Nutt.
- Solidago Glutinosa Nutt. ssp. randii (Porter) Cronquist
- Solidago Glutinosa Nutt. var. chlorolepis (Fernald) Ringius
- Solidago Glutinosa Nutt. var. gillmanii (A. Gray) Cronquist
- Solidago Glutinosa Nutt. var. nana (A. Gray) Cronquist
- Solidago Glutinosa Nutt. var. ontarioensis Ringius
- Solidago Glutinosa Nutt. var. racemosa (Greene) Cronquist
- Solidago Gracilis Poir.
- Solidago Graminea (Wooton & Standl.) S.F. Blake
- Solidago Graminifolia (L.) Salisb.
- Solidago Graminifolia (L.) Salisb. var. galetorum (Greene) House
- Solidago Graminifolia (L.) Salisb. var. gymnospermoides (Greene) Croat
- Solidago Graminifolia (L.) Salisb. var. major (Michx.) Fernald
- Solidago Graminifolia (L.) Salisb. var. media (Greene) S.K. Harris
- Solidago Graminifolia (L.) Salisb. var. nuttallii (Greene) Fernald
- Solidago Graminifolia (L.) Salisb. var. polycephala (Fernald) Fernald
- Solidago Grandiflora Raf.
- Solidago Gymnospermoides (Greene) Fernald
- Solidago Gymnospermoides (Greene) Fernald var. callosa S.K. Harris
- Solidago Harperi Mack.
- Solidago Harrisii Steele
- Solidago Helleri Small
- Solidago Hirsutissima Mill.
- Solidago Hirtella (Greene) Bush
- Solidago Houghtonii Torr. & A. Gray ex A. Gray
- Solidago Howellii Wooton & Standl.
- Solidago Jacksonii (Kuntze) Fernald
- Solidago Jacksonii (Kuntze) Fernald var. humilis (Porter) Beaudry
- Solidago Jejunifolia Steele
- Solidago Juncea Aiton var. neobohemica Fernald
- Solidago Juncea Aiton var. ramosa Porter & Britton
- Solidago Lateriflora L.
- Solidago Latifolia L.
- Solidago Lepida DC.
- Solidago Lepida DC. var. elongata (Nutt.) Fernald
- Solidago Lepida DC. var. fallax Fernald
- Solidago Lepida DC. var. molina Fernald
- Solidago Leptocephala Torr. & A. Gray
- Solidago Lindheimeriana Scheele
- Solidago Longipetiolata Mack. & Bush
- Solidago Lunellii Rydb.
- Solidago Macrophylla Pursh var. thyrsoidea (E. Mey.) Fernald
- Solidago Maxonii Pollard
- Solidago Media (Greene) Bush
- Solidago Mensalis Fernald
- Solidago Mexicana L.
- Solidago Microcephala (Greene) Bush
- Solidago Microphylla (A. Gray) Engelm. ex Small
- Solidago Microphylla (Greene) Bush
- Solidago Milleriana Mack.
- Solidago Minor (Michx.) Fernald
- Solidago Mirabilis Small
- Solidago Missouriensis Nutt. var. extraria A. Gray
- Solidago Missouriensis Nutt. var. glaberrima (M. Martens) Rosend. & Cronquist
- Solidago Missouriensis Nutt. var. montana A. Gray
- Solidago Monticola Torr. & A. Gray
- Solidago Moseleyi Fernald
- Solidago Multiradiata Aiton ssp. scopulorum (A. Gray) W.A. Weber
- Solidago Nashii Small
- Solidago Neglecta Torr. & A. Gray
- Solidago Nemoralis Aiton ssp. decemflora (DC.) Brammall
- Solidago Nemoralis Aiton ssp. haleana (Fernald) G.W. Douglas
- Solidago Nemoralis Aiton ssp. longipetiolata (Mack. & Bush) G.W. Douglas
- Solidago Nemoralis Aiton var. decemflora (DC.) Fernald
- Solidago Nemoralis Aiton var. haleana Fernald
- Solidago Neomexicana (A. Gray) Wooton & Standl.
- Solidago Neurolepis Fernald
- Solidago Nitida Torr. & A. Gray
- Solidago Notabilis Mack.
- Solidago Nuttallii (Greene) Bush
- Solidago Occidentalis (Nutt.) Torr. & A. Gray
- Solidago Ohioensis Frank ex Riddell
- Solidago Oreophila Rydb.
- Solidago Pallida (Porter) Rydb.
- Solidago Parryi (A. Gray) Greene
- Solidago Parvirigida Beaudry
- Solidago Pauciflosculosa Michx.
- Solidago Pendula Small
- Solidago Perglabra Friesner
- Solidago Perlonga Fernald
- Solidago Petiolaris Aiton var. wardii (Britton) Fernald
- Solidago Petiolata auct. non Mill.
- Solidago Petradoria S.F. Blake
- Solidago Pitcheri Nutt.
- Solidago Polycephala Fernald
- Solidago Pruinosa Greene
- Solidago Ptarmicoides (Nees) B. Boivin
- Solidago Pubens M.A. Curtis
- Solidago Pulcherrima A. Nelson
- Solidago Pulverulenta Nutt.
- Solidago Purshii Porter
- Solidago Racemosa Greene
- Solidago Racemosa Greene var. gillmanii (A. Gray) Fernald
- Solidago Randii (Porter) Britton
- Solidago Randii (Porter) Britton var. monticola (Porter) Fernald
- Solidago Remota (Greene) Friesner
- Solidago Riddellii Frank ex Riddell
- Solidago Rigida L.
- Solidago Rigida L. ssp. glabrata (E.L. Braun) Heard & Semple
- Solidago Rigida L. ssp. humilis (Porter) Heard & Semple
- Solidago Rigida L. var. glabrata E.L. Braun
- Solidago Rigida L. var. humilis Porter
- Solidago Rigida L. var. laevicaulis Shinners
- Solidago Rigida L. var. rigida
- Solidago Rigidiuscula (Torr. & A. Gray) Porter
- Solidago Roanensis Porter var. monticola (Torr. & A. Gray) Fernald
- Solidago Rotundifolia DC.
- Solidago Rugosa Mill. var. celtidifolia (Small) Fernald
- Solidago Salicina Elliott
- Solidago Sarothrae Pursh
- Solidago Scaberrima Torr. & A. Gray
- Solidago Scabra Muhl. ex Willd., non Muhl.
- Solidago Scopulorum (A. Gray) A. Nelson
- Solidago Serotina Aiton, non Retz.
- Solidago Serotinoides Á. Löve & D. Löve
- Solidago Simplex Kunth var. gillmanii (A. Gray) Ringius
- Solidago Sparsiflora A. Gray
- Solidago Spathulata DC.
- Solidago Spathulata DC. ssp. glutinosa (Nutt.) D.D. Keck
- Solidago Spathulata DC. ssp. randii (Porter) Gleason
- Solidago Spathulata DC. ssp. spathulata
- Solidago Spathulata DC. var. gillmanii (A. Gray) Gleason
- Solidago Spathulata DC. var. nana (A. Gray) Cronquist
- Solidago Spathulata DC. var. neomexicana (A. Gray) Cronquist
- Solidago Spathulata DC. var. racemosa (Greene) Gleason
- Solidago Spathulata DC. var. subcinerea A. Gray
- Solidago Speciosa Nutt. var. angustata Torr. & A. Gray
- Solidago Speciosa Nutt. var. erecta (Pursh) MacMill.
- Solidago Strigosa Small
- Solidago Suaveolens Schoepf
- Solidago Tarda Mack.
- Solidago Tenuifolia Pursh
- Solidago Tenuifolia Pursh var. pycnocephala Fernald
- Solidago Tenuissima Wooton & Standl.
- Solidago Texensis Friesner
- Solidago Trinervata Greene
- Solidago Uliginosa Nutt. var. jejunifolia (Steele) B. Boivin
- Solidago Uliginosa Nutt. var. neglecta (Torr. & A. Gray) Fernald
- Solidago Uliginosa Nutt. var. peracuta (Fernald) Friesner
- Solidago Uniligulata (DC.) Porter
- Solidago Uniligulata (DC.) Porter var. levipes Fernald
- Solidago Velutina DC. var. nevadensis (A. Gray) C.E.S. Taylor & R.J. Taylor
- Solidago Virgauera L. var. arctica DC.
- Solidago Wardii Britton
- Solidago Yadkinensis (Porter) Small
- Solidago ×bernardii B. Boivin
- Solidago ×hirtipes Fernald
- Solidago ×krotkovii B. Boivin
- Solidago ×leiophallax Friesner
- Solidago ×lutescens (Lindl. ex DC.) B. Boivin
- Solidstem Burnet Saxifrage - Pimpinella Saxifraga L.
- Solidstem Burnet Saxifrage - Pimpinella Saxifraga L. ssp. nigra (Mill.) Gaudin
- Solidstem Burnet Saxifrage - Pimpinella Saxifraga L. ssp. saxifraga
- Soliman's Croton - Croton Soliman Cham. & Schltdl.
- Solitary Clematis - Clematis Integrifolia L.
- Solitary Milkvetch - Astragalus Solitarius M. Peck
- Soliva Anthemifolia (Juss.) R. Br. ex Less.
- Soliva Daucifolia Nutt.
- Soliva Nasturtiifolia auct. non (Juss.) DC.
- Soliva Pterosperma (Juss.) Less.
- Soliva Stolonifera (Brot.) Sweet
- Sollya Fusiformis (Labill.) Briq.
- Sollya - Sollya Lindl.
- Solmsiella Kurzii Steere
- Solmsiella Moss - Solmsiella Biseriata (Austin) Steere
- Solmsiella Moss - Solmsiella Müll. Hal.
- Solomon's Lily - Arum Palestinum Boiss.
- Solomon's Seal - Polygonatum Mill.
- Solorinaria Despreauxii (Mont.) Fink
- Solorinella Lichen - Solorinella Anzi
- Solorinella Lichen - Solorinella Asteriscus Anzi
- Somerset Hair Grass - Koeleria Vallesiana (Honck.) Gaudin
- Sommerfelt's Pore Lichen - Pertusaria Sommerfeltii (Flörke ex Sommerf.) Fr.
- Son's Buckwheat - Eriogonum Natum Reveal
- Sonchus Arvensis L. var. glabrescens Guenth., Grab. & Wimm.
- Sonchus Arvensis L. var. shumovichii B. Boivin
- Sonchus Asper (L.) Hill ssp. asper
- Sonchus Asper (L.) Hill ssp. glaucescens (Jord.) J. Ball
- Sonchus Nymanii Tineo & Guss.
- Sonchus Tataricus L. p.p.
- Sonchus Uliginosus M. Bieb.
- Sonderegger Pine - Pinus ×sondereggeri H.H. Chapm. ex Sudw.
- Sonne's Arnica - Arnica Parryi A. Gray ssp. sonnei (Greene) Maguire
- Sonneratia Alba J.E. Sm.
- Sonneratia L. f.
- Sonoita Nightshade - Solanum Adscendens Sendtn.
- Sonoita Noseburn - Tragia Laciniata (Torr.) Müll. Arg.
- Sonoma Azalea - Rhododendron Occidentale (Torr. & A. Gray) A. Gray var. sonomense (Greene) Rehder
- Sonoma Ceanothus - Ceanothus Sonomensis J.T. Howell
- Sonoma Clarkia - Clarkia Gracilis (Piper) A. Nelson & J.F. Macbr. ssp. sonomensis (C.L. Hitchc.) F
- Sonoma Ground Rose - Rosa Spithamea S. Watson var. sonomensis (Greene) Jeps.
- Sonoma Hedgenettle - Stachys Stricta Greene
- Sonoma Koerberia Lichen - Koerberia Sonomensis (Tuck.) Henssen
- Sonoma Lessingia - Lessingia Ramulosa A. Gray
- Sonoma Lessingia - Lessingia Ramulosa A. Gray var. adenophora (Greene) A. Gray
- Sonoma Lessingia - Lessingia Ramulosa A. Gray var. ramulosa
- Sonoma Manzanita - Arctostaphylos Canescens Eastw. ssp. sonomensis (Eastw.) P.V. Wells
- Sonoma Penstemon - Penstemon Newberryi A. Gray ssp. sonomensis (Greene) D.D. Keck
- Sonoma Shortawn Foxtail - Alopecurus Aequalis Sobol. var. sonomensis P. Rubtzov
- Sonoma Spineflower - Chorizanthe Valida S. Watson
- Sonora Draba - Draba Cuneifolia Nutt. ex Torr. & A. Gray var. sonorae (Greene) Parish
- Sonora Entosthodon Moss - Entosthodon Sonorae (Cardot) Steere
- Sonora False Goldenaster - Heterotheca Marginata Semple
- Sonora Lupine - Lupinus Arizonicus (S. Watson) S. Watson ssp. sonorensis Christian & D. Dunn
- Sonora Rosewood - Vauquelinia Californica (Torr.) Sarg. ssp. sonorensis Hess & Henrickson
- Sonoran Bean - Phaseolus Pedicellatus Benth.
- Sonoran Beardtongue - Penstemon Stenophyllus (A. Gray) Howell
- Sonoran Bird's-foot Trefoil - Lotus Alamosanus (Rose) Gentry
- Sonoran Brickellbush - Brickellia Simplex A. Gray
- Sonoran Chinchweed - Pectis Cylindrica (Fernald) Rydb.
- Sonoran Cloak Fern - Notholaena Grayi Davenport ssp. sonorensis Windham
- Sonoran Croton - Croton Sonorae Torr.
- Sonoran Desertdandelion - Malacothrix Sonorae W.S. Davis & P.H. Raven
- Sonoran Dodder - Cuscuta Erosa Yunck.
- Sonoran False Prairie-clover - Marina Orcuttii (S. Watson) Barneby
- Sonoran Giant Hyssop - Agastache Wrightii (Greenm.) Wooton & Standl.
- Sonoran Globe Amaranth - Gomphrena Sonorae Torr.
- Sonoran Indian Mallow - Abutilon Mollicomum (Willd.) Sweet
- Sonoran Indigo - Indigofera Sphaerocarpa A. Gray
- Sonoran Maiden Fern - Thelypteris Puberula (Baker) Morton var. sonorensis A.R. Sm.
- Sonoran Milkvine - Matelea Cordifolia (A. Gray) Woodson
- Sonoran Neststraw - Stylocline Sonorensis Wiggins
- Sonoran Nightshade - Solanum Lumholtzianum Bartlett
- Sonoran Oak - Quercus Viminea Trel.
- Sonoran Panicgrass - Panicum Hirticaule J. Presl var. stramineum (Hitchc. & Chase) Beetle
- Sonoran Prairie Clover - Dalea Filiformis A. Gray
- Sonoran Pricklyleaf - Thymophylla Concinna (A. Gray) Strother
- Sonoran Pricklypoppy - Argemone Gracilenta Greene
- Sonoran Sandmat - Chamaesyce Micromera (Boiss. ex Engelm.) Wooton & Standl.
- Sonoran Scrub Oak - Quercus Turbinella Greene
- Sonoran Silverbush - Argythamnia Brandegeei Millsp.
- Sonoran Silverbush - Argythamnia Brandegeei Millsp. var. brandegeei Millsp. [excluded]
- Sonoran Silverbush - Argythamnia Brandegeei Millsp. var. intonsa (I.M. Johnst.) J.W. Ingram ex L.C. Wheeler
- Sonoran Thoroughwort - Fleischmannia Sonorae (A. Gray) R.M. King & H. Rob.
- Sonoran Ticktrefoil - Desmodium Scopulorum S. Watson
- Sonoran Water-willow - Justicia Sonorae Wassh.
- Soot Lichen - Cyphelium Ach.
- Soot Lichen - Cyphelium Brachysporum Nadv.
- Soot Lichen - Cyphelium Brunneum W.A. Weber
- Soot Lichen - Cyphelium Chloroconium (Tuck.) Zahlbr.
- Soot Lichen - Cyphelium Inquinans (Sm.) Trevis.
- Soot Lichen - Cyphelium Karelicum (Vain.) Rasanen
- Soot Lichen - Cyphelium Lucidum (Th. Fr.) Th. Fr.
- Soot Lichen - Cyphelium Pinicola Tibell
- Soot Lichen - Cyphelium Tigillare (Ach.) Ach.
- Soot Lichen - Cyphelium Trachylioides (Nyl. ex Branth & Rostrup) Erichsen
- Sophia Andrenarium Cockerell
- Sophia Andrenarium Cockerell var. osmiarum Cockerell
- Sophia Brachycarpa (Richardson) Rydb.
- Sophia Filipes (A. Gray) A. Heller
- Sophia Glabra Wooton & Standl.
- Sophia Halictorum Cockerell
- Sophia Hartwegiana (Fourn.) Greene
- Sophia Incisa (Engelm. ex A. Gray) Greene
- Sophia Intermedia Rydb.
- Sophia Millefolia Rydb. ex Britton
- Sophia Multifida (Pursh) O.E. Schulz
- Sophia Nelsonii Rydb.
- Sophia Ochroleuca Wooton
- Sophia Paradisa A. Nelson & Kennedy
- Sophia Pinnata (Walter) Howell
- Sophia Procera Greene
- Sophia Richardsonii (O.E. Schulz) Rydb.
- Sophia Sophia (L.) Britton, nom. inval.
- Sophia Viscosa Rydb.
- Sophisticated Graphina Lichen - Graphina Sophisticascens (Nyl.) Zahlbr.
- Sophora Affinis Torr. & A. Gray
- Sophora Arizonica S. Watson ssp. formosa (Kearney & Peebles) Yakovlev
- Sophora Arizonica S. Watson var. formosa (Kearney & Peebles) Tsoong
- Sophora Chrysophylla (Salisb.) Seem. ssp. circularis Chock
- Sophora Chrysophylla (Salisb.) Seem. ssp. glabrata (A. Gray) Chock
- Sophora Chrysophylla (Salisb.) Seem. ssp. unifoliata (Rock) Chock
- Sophora Chrysophylla (Salisb.) Seem. var. elliptica Chock
- Sophora Chrysophylla (Salisb.) Seem. var. glabrata (A. Gray) Chock
- Sophora Chrysophylla (Salisb.) Seem. var. grisea (O. Deg. & Sherff) Chock
- Sophora Chrysophylla (Salisb.) Seem. var. kanaioensis Chock
- Sophora Chrysophylla (Salisb.) Seem. var. kauensis Chock
- Sophora Chrysophylla (Salisb.) Seem. var. lanaiensis Chock
- Sophora Chrysophylla (Salisb.) Seem. var. makuaensis Chock
- Sophora Chrysophylla (Salisb.) Seem. var. ovata Chock
- Sophora Chrysophylla (Salisb.) Seem. var. unifoliata (Rock) Chock
- Sophora Davidii (Franch.) Skeels
- Sophora Formosa Kearney & Peebles
- Sophora Japonica L.
- Sophora Kentukea Dum. Cours.
- Sophora Littoralis Schrad.
- Sophora Sericea Nutt.
- Sophora Tomentosa L. ssp. bahamensis Yakovlev
- Sophora Tomentosa L. ssp. littoralis (Schrad.) Yakovlev
- Sophora Tomentosa L. ssp. occidentalis (L.) Brummitt
- Sophora Velutina Lindl.
- Sophora Velutina Lindl. ssp. zimbabweensis J.B. Gillett & Brummitt
- Sophronanthe Hispida Benth. ex Lindl.
- Sophronanthe Pilosa (Michx.) Small
- Sopubia Buchenau-ham. ex D.Don
- Sopubia Mannii Skan
- Soralpouch Fern - Saccoloma Kaulf.
- Sorbaria Arborea C.K. Schneid.
- Sorbaria Sorbifolia (L.) A. Braun var. stellipila Maxim.
- Sorbaria Tomentosa (Lindl.) Rehder
- Sorbaronia - ×sorbaronia Arsenii (Britton ex Arsene) G.N. Jones
- Sorbaronia - ×sorbaronia C.k. Schneid.
- Sorbaronia - ×sorbaronia Jackii Rehder
- Sorbus Alnifolia (Siebold & Zucc.) K. Koch
- Sorbus Alpina (Willd.) Heynh.
- Sorbus Arbutifolia (L.) Heynh.
- Sorbus Arbutifolia (L.) Heynh. var. atropurpurea (Britton) C.K. Schneid.
- Sorbus Aucuparia L. var. xanthocarpa Hartwig & Rümpler
- Sorbus Cascadensis G.N. Jones
- Sorbus Commixta Hedl.
- Sorbus Decora (Sarg.) C.K. Schneid. var. groenlandica (C.K. Schneid.) G.N. Jon
- Sorbus Domestica L. [excluded]
- Sorbus Melanocarpa (Michx.) Heynh.
- Sorbus Occidentalis (S. Watson) Greene
- Sorbus Pinnatifida (Ehrh.) Bean
- Sorbus Sargentii Dippel
- Sorbus Sitchensis M. Roem. ssp. californica (Greene) Abrams
- Sorbus Sitchensis M. Roem. ssp. grayi (Wenzig) Calder & Roy L. Taylor
- Sorbus Sorbifolia (Poir.) Hedl.
- Sorbus Tianschanica Rupr.
- Sordid Pepperweed - Lepidium Sordidum A. Gray
- Soredia Cartilage Lichen - Ramalina Sorediantha Nyl.
- Sorensen's Catchfly - Silene Sorensenis (B. Boivin) Bocquet
- Sorghastrum Apalachicolense D.W. Hall
- Sorghastrum Avenaceum (Michx.) Nash
- Sorghastrum Parviflorum auct. non (Desv.) Hitchc. & Chase
- Sorghum Aethiopicum (Hack.) Rupr. ex Stapf
- Sorghum Arundinaceum (Desv.) Stapf
- Sorghum Bicolor (L.) Moench var. aethiopicum (Hack.) de Wet & Huckabay
- Sorghum Bicolor (L.) Moench var. caffrorum (Retz.) Mohlenbr.
- Sorghum Bicolor (L.) Moench var. drummondii (Nees ex Steud.) Mohlenbr.
- Sorghum Bicolor (L.) Moench var. sudanense (Piper) Hitchc.
- Sorghum Bicolor (L.) Moench var. virgatum (Hack.) de Wet & Huckabay
- Sorghum Caffrorum (Retz.) P. Beauv.
- Sorghum Caudatum (Hack.) Stapf
- Sorghum Cernuum (Ard.) Host
- Sorghum Dochna (Forssk.) Snowden
- Sorghum Dochna (Forssk.) Snowden var. technicum (Koern.) Snowden
- Sorghum Drummondii (Nees ex Steud.) Millsp. & Chase
- Sorghum Durra (Forssk.) Stapf
- Sorghum Guineense Stapf
- Sorghum Lanceolatum Stapf
- Sorghum Miliaceum (Roxb.) Snowden
- Sorghum Nervosum Besser ex Schult.
- Sorghum Saccharatum (L.) Moench, nom. utique rej.
- Sorghum - Sorghum Bicolor (L.) Moench
- Sorghum - Sorghum Moench
- Sorghum - Sorghum Propinquum (Kunth) Hitchc.
- Sorghum Subglabrescens Schweinf. & Asch.
- Sorghum Sudanense (Piper) Stapf
- Sorghum Verticilliflorum (Steud.) Stapf
- Sorghum Virgatum (Hack.) Stapf
- Sorghum Vulgare Pers.
- Sorghum Vulgare Pers. var. caffrorum (Retz.) Hubbard & Rehder
- Sorghum Vulgare Pers. var. drummondii (Nees ex Steud.) Hack. ex Chiov.
- Sorghum Vulgare Pers. var. durra (Forssk.) Hubbard & Rehder
- Sorghum Vulgare Pers. var. roxburghii (Stapf) Haines
- Sorghum Vulgare Pers. var. saccharatum (L.) Boerl., nom. utique rej.
- Sorghum Vulgare Pers. var. sudanense (Piper) Hitchc.
- Sorghum Vulgare Pers. var. technicum (Koern.) Jáv.
- Sorrel Buckwheat - Eriogonum Polycladon Benth.
- Sorrel - Oxalis Macrocarpa (Small) R. Knuth
- Sorrel - Oxalis Nelsonii (Small) R. Knuth
- Sorrel - Oxalis Regnellii Miq.
- Sorrel - Oxalis Rosea Feuillee ex Jacq.
- Sorrelvine - Cissus Trifoliata (L.) L.
- Sorrie's Heartleaf - Hexastylis Sorriei Gaddy
- Sortbeard Plumegrass - Saccharum Brevibarbe (Michx.) Pers. var. contortum (Elliott) R. Webster
- Sotol - Dasylirion Zucc.
- Souari Nut - Caryocar Nuciferum L.
- Soulamea Lam.
- Soulard Crab - Malus ×soulardii (L.H. Bailey) Britton (pro sp.)
- Sour Cherry - Prunus Cerasus L.
- Sour Orange - Citrus ×aurantium L. (pro sp.)
- Sour Orange - Citrus ×aurantium L. ssp. aurantium
- Sour Pricklypear - Consolea Rubescens (Salm-Dyck ex DC.) Lem.
- Sourgrass - Digitaria Insularis (L.) Mez ex Ekman
- Soursop - Annona Muricata L.
- Sourthern Woodrush - Luzula Forsteri (Sm.) DC.
- Sourwood - Oxydendrum Arboreum (L.) DC.
- Sourwood - Oxydendrum Dc.
- South African Hoarypea - Tephrosia Noctiflora Bojer ex Baker
- South African Lovegrass - Eragrostis Plana Nees
- South African Oatgrass - Karroochloa Conert & Türpe
- South African Oatgrass - Karroochloa Purpurea (L. f.) Conert & Türpe
- South African Ragwort - Senecio Inaequidens DC.
- South American Amazonvine - Stigmaphyllon Puberum (Rich.) A. Juss.
- South American Bonnet Orchid - Pleurothallis Obovata (Lindl.) Lindl.
- South American Evening Primrose - Oenothera Pubescens Willd. ex Spreng.
- South American Jelly Palm - Butia Capitata (Mart.) Becc.
- South American Mexican Clover - Richardia Humistrata (Cham. & Schltdl.) Schult. & Schult. f.
- South American Mock Vervain - Glandularia Pulchella (Sweet) Troncoso
- South American Rice Grass - Jarava Plumosa (Spreng.) S.L.W. Jacobs & J. Everett
- South American Rubberweed - Hymenoxys Anthemoides (Juss.) Cass.
- South American Saltbush - Atriplex Lampa Gillies ex Moq.
- South American Skullcap - Scutellaria Racemosa Pers.
- South American Tobacco - Nicotiana Sylvestris Speg. & Comes
- South American Waterweed - Elodea Callitrichoides (Rich.) Caspary
- South Idaho Onion - Allium Aaseae Ownbey
- South Idaho Penstemon - Penstemon Attenuatus Douglas ex Lindl. var. militaris (Greene) Cronquist
- South Texas Blanketflower - Gaillardia Aestivalis (Walter) H. Rock var. austrotexana B.L. Turner
- South Texas Prairie Clover - Dalea Austrotexana B.L. Turner
- South Wales Wattle - Acacia Parramattensis Tindale
- Southeastern Annual Saltmarsh Aster - Symphyotrichum Squamatum (Spreng.) G.L. Nesom
- Southeastern Primrose-willow - Ludwigia Linifolia Poir.
- Southeastern Sneezeweed - Helenium Pinnatifidum (Nutt.) Rydb.
- Southeastern Sunflower - Helianthus Agrestis Pollard
- Southeastern Wildrye - Elymus Glabriflorus (Vasey ex L.H. Dewey) Scribn. & C.R. Ball
- Southern Adderstongue - Ophioglossum Vulgatum L.
- Southern Alpine Buckwheat - Eriogonum Kennedyi Porter ex S. Watson var. alpigenum Munz & I.M. Johnst.
- Southern Amaranth - Amaranthus Australis (A. Gray) Sauer
- Southern Annual Saltmarsh Aster - Symphyotrichum Divaricatum (Nutt.) G.L. Nesom
- Southern Arrowwood - Viburnum Dentatum L.
- Southern Arrowwood - Viburnum Dentatum L. var. dentatum
- Southern Arrowwood - Viburnum Dentatum L. var. venosum (Britton) Gleason
- Southern Arrowwood - Viburnum Recognitum Fernald
- Southern Balsampear - Momordica Balsamina L.
- Southern Barbara's Buttons - Marshallia Ramosa Beadle & F.E. Boynt.
- Southern Bayberry - Morella Caroliniensis (Mill.) Small
- Southern Beaksedge - Rhynchospora Microcarpa Baldw. ex A. Gray
- Southern Beeblossom - Oenothera Simulans (Small) W.L. Wagner & Hoch
- Southern Beech - Nothofagus Blume, nom. cons.
- Southern Bladderwort - Utricularia Juncea Vahl
- Southern Blue Monkshood - Aconitum Uncinatum L.
- Southern Blue Monkshood - Aconitum Uncinatum L. ssp. muticum (DC.) Hardin
- Southern Blue Monkshood - Aconitum Uncinatum L. ssp. uncinatum
- Southern Blueberry - Vaccinium Formosum Andrews
- Southern Bluet - Houstonia Micrantha (Shinners) Terrell
- Southern Bluethread - Burmannia Capitata (J.F. Gmel.) Mart.
- Southern Bog Clubmoss - Lycopodiella Appressa (Chapm.) Cranfill
- Southern Bogbutton - Lachnocaulon Beyrichianum Sporleder ex Koern.
- Southern Brackenfern - Pteridium Caudatum (L.) Maxon
- Southern Bush Honeysuckle - Diervilla Sessilifolia Buckley
- Southern Bush Monkeyflower - Diplacus Longiflorus Nutt.
- Southern Butterwort - Pinguicula Primuliflora Alph. Wood & Godfrey
- Southern California Draba - Draba Corrugata S. Watson
- Southern California Draba - Draba Corrugata S. Watson var. corrugata
- Southern California Draba - Draba Corrugata S. Watson var. saxosa (Davidson) Munz & I.M. Johnst.
- Southern California Walnut - Juglans Californica S. Watson
- Southern Catalpa - Catalpa Bignonioides Walter
- Southern Cattail - Typha Domingensis Pers.
- Southern Chinese Pine - Pinus Tabuliformis Carrière
- Southern Coastal Violet - Viola Septemloba Leconte
- Southern Colicroot - Aletris Obovata Nash
- Southern Crab Apple - Malus Angustifolia (Aiton) Michx.
- Southern Crab Apple - Malus Angustifolia (Aiton) Michx. var. angustifolia
- Southern Crab Apple - Malus Angustifolia (Aiton) Michx. var. puberula Rehder
- Southern Crabgrass - Digitaria Ciliaris (Retz.) Koeler
- Southern Cutgrass - Leersia Hexandra Sw.
- Southern Dawnflower - Stylisma Humistrata (Walter) Chapm.
- Southern Dewberry - Rubus Trivialis Michx.
- Southern False Serviceberry - Malacomeles Denticulata (Kunth) Engelm.
- Southern Fimbry - Fimbristylis Decipiens Kral
- Southern Flatsedge - Cyperus Thyrsiflorus Jungh.
- Southern Flax - Linum Australe A. Heller
- Southern Flax - Linum Australe A. Heller var. australe
- Southern Flax - Linum Australe A. Heller var. glandulosum C.M. Rogers
- Southern Florida Sandmat - Chamaesyce Adenoptera (Bertol.) Small
- Southern Florida Sandmat - Chamaesyce Adenoptera (Bertol.) Small ssp. pergamena (Small) Burch
- Southern Fogfruit - Phyla Stoechadifolia (L.) Small
- Southern Gilia - Saltugilia Australis (H. Mason & A.D. Grant) L.A. Johnson
- Southern Globethistle - Echinops Ritro L.
- Southern Globethistle - Echinops Ritro L. ssp. ruthenicus (M. Bieb.) Nyman
- Southern Goldenbush - Isocoma Pluriflora (Torr. & A. Gray) Greene
- Southern Hawkweed - Hieracium Argutum Nutt.
- Southern Hawthorn - Crataegus Contrita Beadle
- Southern Hayscented Fern - Dennstaedtia Globulifera (Poir.) Hieron.
- Southern Honeysuckle - Lonicera Subspicata Hook. & Arn.
- Southern Honeysuckle - Lonicera Subspicata Hook. & Arn. var. subspicata
- Southern Island Mallow - Lavatera Assurgentiflora Kellogg ssp. glabra Philbrick
- Southern Island Phacelia - Phacelia Floribunda Greene
- Southern Jewelflower - Streptanthus Campestris S. Watson
- Southern Jointweed - Polygonella Americana (Fisch. & C.A. Mey.) Small
- Southern Lady's Tresses - Spiranthes Torta (Thunb.) Garay & H.R. Sweet
- Southern Lipfern - Cheilanthes Microphylla (Sw.) Sw.
- Southern Lobelia - Lobelia Amoena Michx.
- Southern Lobelia - Lobelia Amoena Michx. var. amoena
- Southern Lobelia - Lobelia Amoena Michx. var. glandulifera A. Gray
- Southern Long Sedge - Carex Lonchocarpa Willd.
- Southern Magnolia - Magnolia Grandiflora L.
- Southern Mahogany - Eucalyptus Botryoides Sm.
- Southern Marsh Yellowcress - Rorippa Teres (Michx.) R. Stuckey
- Southern Meadow-rue - Thalictrum Debile Buckley
- Southern Medick - Medicago Turbinata (L.) All.
- Southern Mexican Sage - Salvia Disjuncta Fernald
- Southern Milkweed - Asclepias Viridula Chapm.
- Southern Monardella - Monardella Australis Abrams
- Southern Mountain Buckwheat - Eriogonum Kennedyi Porter ex S. Watson var. austromontanum Munz & I.M. Johnst.
- Southern Mountain Cranberry - Vaccinium Erythrocarpum Michx.
- Southern Mountain Misery - Chamaebatia Australis (Brandegee) Abrams
- Southern Mountainmint - Pycnanthemum Pycnanthemoides (Leavenworth) Fernald
- Southern Mountainmint - Pycnanthemum Pycnanthemoides (Leavenworth) Fernald var. pycnanthemoides
- Southern Mountainmint - Pycnanthemum Pycnanthemoides (Leavenworth) Fernald var. viridifolium Fernald
- Southern Mule-ears - Agnorhiza Ovata (Torr. & A. Gray ex Torr.) W.A. Weber
- Southern Needleleaf - Tillandsia Setacea Sw.
- Southern Oregon Buttercup - Ranunculus Austrooreganus L.D. Benson
- Southern Pea - Vigna Unguiculata (L.) Walp. ssp. unguiculata
- Southern Pepperwort - Lepidium Austrinum Small
- Southern Pokeweed - Phytolacca Bogotensis Kunth
- Southern Prairie Aster - Eurybia Hemispherica (Alexander) G.L. Nesom
- Southern Purple Pitcherplant - Sarracenia Purpurea L. var. venosa (Raf.) Fernald
- Southern Quillwort - Isoetes Flaccida Shuttlw. ex A. Braun
- Southern Quillwort - Isoetes Flaccida Shuttlw. ex A. Braun var. alata N.E. Pfeiffer
- Southern Quillwort - Isoetes Flaccida Shuttlw. ex A. Braun var. flaccida
- Southern Red Oak - Quercus Falcata Michx.
- Southern Redcedar - Juniperus Virginiana L. var. silicicola (Small) Silba
- Southern Rockbell - Wahlenbergia Marginata (Thunb.) A. DC.
- Southern Sandbur - Cenchrus Echinatus L.
- Southern Sedge - Carex Austrina (Small) Mack.
- Southern Shagbark Hickory - Carya Carolinae-septentrionalis (Ashe) Engl. & Graebn.
- Southern Sierra Phacelia - Phacelia Austromontana J.T. Howell
- Southern Sierra Pincushion - Chaenactis Alpigena Sharsm.
- Southern Spicebush - Lindera Melissifolia (Walter) Blume
- Southern Succisella - Succisella Inflexa (Kluk) G. Beck
- Southern Sugar Maple - Acer Floridanum (Chapm.) Pax
- Southern Suncup - Camissonia Bistorta (Nutt. ex Torr. & A. Gray) P.H. Raven
- Southern Swamp Aster - Eurybia Paludosa (Aiton) G.L. Nesom
- Southern Threeawn - Aristida Simpliciflora Chapm.
- Southern Threecornerjack - Emex Australis Steinh.
- Southern Twayblade - Listera Australis Lindl.
- Southern Umbrella-sedge - Fuirena Scirpoidea Michx.
- Southern Umbrellawort - Tauschia Arguta (Torr. & A. Gray) J.F. Macbr.
- Southern Watergrass - Luziola Fluitans (Michx.) Terrell & H. Rob.
- Southern Waternymph - Najas Guadalupensis (Spreng.) Magnus
- Southern Waternymph - Najas Guadalupensis (Spreng.) Magnus ssp. guadalupensis
- Southern Waxy Sedge - Carex Glaucescens Elliott
- Southern Whitetop - Doellingeria Sericocarpoides Small
- Southern Woodfern - Dryopteris Ludoviciana (Kunze) Small
- Southern Woodland Violet - Viola Hirsutula Brainerd
- Southern Yellow Loosestrife - Lysimachia Tonsa (Alph. Wood) Alph. Wood ex Pax & R. Knuth
- Southernwood - Artemisia Abrotanum L.
- Southwest Fescue - Festuca Calligera (Piper) Rydb.
- Southwestern Annual Saltmarsh Aster - Symphyotrichum Expansum (Poepp. ex Spreng.) G.L. Nesom
- Southwestern Beardtongue - Penstemon Laevis Pennell
- Southwestern Bedstraw - Galium Virgatum Nutt.
- Southwestern Brickellbush - Brickellia Conduplicata (B.L. Rob.) B.L. Rob.
- Southwestern Bristlegrass - Setaria Scheelei (Steud.) Hitchc.
- Southwestern Cosmos - Cosmos Parviflorus (Jacq.) Pers.
- Southwestern Cryptantha - Cryptantha Mensana (M.E. Jones) Payson
- Southwestern False Cloak Fern - Argyrochosma Limitanea (Maxon) Windham
- Southwestern False Cloak Fern - Argyrochosma Limitanea (Maxon) Windham ssp. limitanea
- Southwestern False Cloak Fern - Argyrochosma Limitanea (Maxon) Windham ssp. mexicana (Maxon) Windham
- Southwestern Gilia - Gilia Austrooccidentalis (A.D. Grant & V.E. Grant) A.D. Grant & V.E. Grant
- Southwestern Groundcherry - Physalis Caudella Standl.
- Southwestern Mock Vervain - Glandularia Gooddingii (Briq.) Solbrig
- Southwestern Muhly - Muhlenbergia Palmeri Vasey
- Southwestern Needlegrass - Achnatherum Eminens (Cav.) Barkworth
- Southwestern Phacelia - Phacelia Glaberrima (Torr. ex S. Watson) J.T. Howell
- Southwestern Pleatleaf - Nemastylis Tenuis (Herb.) Benth.
- Southwestern Pricklypoppy - Argemone Pleiacantha Greene
- Southwestern Pricklypoppy - Argemone Pleiacantha Greene ssp. ambigua G.B. Ownbey
- Southwestern Pricklypoppy - Argemone Pleiacantha Greene ssp. pinnatisecta G.B. Ownbey
- Southwestern Pricklypoppy - Argemone Pleiacantha Greene ssp. pleiacantha
- Southwestern Rabbitbrush - Chrysothamnus Pulchellus (A. Gray) Greene
- Southwestern Ringstem - Anulocaulis Leiosolenus (Torr.) Standl.
- Southwestern Ringstem - Anulocaulis Leiosolenus (Torr.) Standl. var. howardii Spellenb. & Wootten
- Southwestern Ringstem - Anulocaulis Leiosolenus (Torr.) Standl. var. lasianthus I.M. Johnst.
- Southwestern Ringstem - Anulocaulis Leiosolenus (Torr.) Standl. var. leiosolenus
- Southwestern Showy Sedge - Carex Bella L.H. Bailey
- Southwestern Waterwort - Elatine Rubella Rydb.
- Southwestern White Pine Dwarf Mistletoe - Arceuthobium Blumeri A. Nelson
- Southwestern White Pine - Pinus Strobiformis Engelm.
- Sowthistle Desertdandelion - Malacothrix Sonchoides (Nutt.) Torr. & A. Gray
- Sowthistle - Sonchus L.
- Soxman's Milkvetch - Astragalus Soxmaniorum Lundell
- Soybean - Glycine Max (L.) Merr.
- Soybean - Glycine Willd.
- Spach's Evening Primrose - Oenothera Spachiana Torr. & A. Gray
- Spadeleaf - Centella Asiatica (L.) Urb.
- Spalding's Milkvetch - Astragalus Spaldingii A. Gray
- Spalding's Orange Lichen - Caloplaca Spaldingii Zahlbr.
- Spalding's Silene - Silene Spaldingii S. Watson
- Spanish Arborvine - Merremia Tuberosa (L.) Rendle
- Spanish Bayonet - Yucca Harrimaniae Trel.
- Spanish Bayonet - Yucca Harrimaniae Trel. var. harrimaniae
- Spanish Bayonet - Yucca Harrimaniae Trel. var. sterilis Neese & S.L. Welsh
- Spanish Broom - Spartium Junceum L.
- Spanish Cedar - Cedrela Odorata L.
- Spanish Cherry - Mimusops Elengi L.
- Spanish Clover - Trifolium Gemellum Pourr. ex Willd.
- Spanish Elder - Piper Swartzianum (Miq.) C. DC.
- Spanish Elm - Cordia Alliodora (Ruiz & Pav.) Oken
- Spanish False Fleabane - Pulicaria Paludosa Link
- Spanish Fennel - Nigella Hispanica L.
- Spanish Gold - Grindelia Papposa G.L. Nesom & Suh
- Spanish Heath - Erica Lusitanica K. Rudolphi
- Spanish Iris - Iris Xiphium L.
- Spanish Lady - Opuntia Triacantha (Willd.) Sweet
- Spanish Lime - Melicoccus Bijugatus Jacq.
- Spanish Lupine - Lupinus Hispanicus Boiss. & Reut.
- Spanish Lupine - Lupinus Hispanicus Boiss. & Reut. ssp. bicolor (Merino) Gladst.
- Spanish Moss - Tillandsia Usneoides (L.) L.
- Spanish Needle Onion - Allium Shevockii McNeal
- Spanish Needles - Bidens Bipinnata L.
- Spanish Stenocereus - Stenocereus Fimbriatus (Lam.) Lourteig
- Spanish Stonecrop - Sedum Hispanicum L.
- Spanish Thyme - Lippia Micromera Schauer
- Spanish Thyme - Lippia Micromera Schauer var. helleri (Britton) Moldenke
- Sparaxis Grandiflora (D. Delar.) Ker Gawl.
- Sparganium Acaule (Beeby ex Macoun) Rydb.
- Sparganium Androcladum (Engelm.) Morong var. fluctuans Engelm. ex Morong
- Sparganium Californicum Greene
- Sparganium Chlorocarpum Rydb.
- Sparganium Chlorocarpum Rydb. var. acaule (Beeby ex Macoun) Fernald
- Sparganium Emersum Rehmann ssp. emersum
- Sparganium Emersum Rehmann var. angustifolium (Michx.) Roy L. Taylor & MacBryde
- Sparganium Emersum Rehmann var. multipedunculatum (Morong) Reveal
- Sparganium Erectum L. var. glomeratum Beurling ex Laest.
- Sparganium Eurycarpum Engelm. ssp. eurycarpum
- Sparganium Eurycarpum Engelm. var. greenei (Morong) Graebn.
- Sparganium Greenei Morong
- Sparganium Lucidum Fernald & Eames
- Sparganium Minimum (L.) Fr., nom. illeg.
- Sparganium Minimum Wallr.
- Sparganium Multipedunculatum (Morong) Rydb.
- Sparganium Natans L. var. minimum L.
- Sparganium Simplex Huds.
- Sparrow False Pimpernel - Lindernia Antipoda (L.) Alston
- Sparrowegg Lady's Slipper - Cypripedium Passerinum Richardson
- Sparse-flowered Bog Orchid - Platanthera Sparsiflora (S. Watson) Schltr.
- Sparse-flowered Bog Orchid - Platanthera Sparsiflora (S. Watson) Schltr. var. ensifolia (Rydb.) Luer
- Sparse-flowered Bog Orchid - Platanthera Sparsiflora (S. Watson) Schltr. var. sparsiflora
- Sparse-leaved St. Johnswort - Hypericum Erythreae (Spach) Steud.
- Sparseflower Jewelflower - Streptanthus Sparsiflorus Rollins
- Sparseflower Sedge - Carex Tenuiflora Wahlenb.
- Sparseleaf Cinquefoil - Potentilla Brevifolia Nutt. ex Torr. & A. Gray
- Sparselobe Grapefern - Botrychium Biternatum (Sav.) Underw.
- Spartina Alterniflora Loisel. var. glabra (Muhl. ex Bigelow) Fernald
- Spartina Alterniflora Loisel. var. pilosa (Merr.) Fernald
- Spartina Bakeri (Merr.) P.M. Peterson & Saarela
- Spartina Cynosuroides (L.) Roth var. polystachya (Michx.) Beal ex Fernald
- Spartina Michauxiana Hitchc.
- Spartina Patens (Aiton) Muhl. var. caespitosa (A.A. Eaton) Hitchc.
- Spartina Patens (Aiton) Muhl. var. juncea (Michx.) Hitchc.
- Spartina Patens (Aiton) Muhl. var. monogyna (M.A. Curtis) Fernald
- Spartina Pectinata Bosc ex Link var. suttiei (Farw.) Fernald
- Spartina Pumila Roth
- Spartina Stricta (Aiton) Roth
- Spathiger Ramosus (Jacq.) Britton
- Spathiger Rigidus (Jacq.) Small
- Spathiger Strobilifera (Rchb. f.) Small
- Spathiphyllum - Spathiphyllum Schott
- Spathodea - Spathodea P. Beauv.
- Spathoglottis Elmeri Ames [excluded]
- Spathularia Michauxii (Britton) Small
- Spathulata Spuria (M. Bieb.) Á. Löve & D. Löve
- Spathulate Botrychium - Botrychium Spathulatum W.H. Wagner
- Spathulate Candle Snuffer Moss - Encalypta Spathulata Müll. Hal.
- Spathyema Foetida (L.) Raf.
- Spatulaleaf Loosestrife - Lythrum Portula (L.) D.A. Webb
- Spatularia Foliolosa (R. Br.) Small
- Spatularia Stellaris (L.) Haw.
- Spear Globemallow - Sphaeralcea Hastulata A. Gray
- Spear Saltbush - Atriplex Patula L.
- Spearbract Blue-eyed Grass - Sisyrinchium Sagittiferum E.P. Bicknell
- Speargrass - Piptochaetium J. Presl
- Spearhead - Chlorocrambe Hastata (S. Watson) Rydb.
- Spearleaf Agoseris - Agoseris Retrorsa (Benth.) Greene
- Spearleaf Arnica - Arnica Longifolia D.C. Eaton
- Spearleaf Brickellbush - Brickellia Atractyloides A. Gray
- Spearleaf Buckwheat - Eriogonum Lonchophyllum Torr. & A. Gray
- Spearleaf Buckwheat - Eriogonum Lonchophyllum Torr. & A. Gray var. fendlerianum (Benth.) Reveal
- Spearleaf Buckwheat - Eriogonum Lonchophyllum Torr. & A. Gray var. intermontanum (Reveal) Reveal
- Spearleaf Buckwheat - Eriogonum Lonchophyllum Torr. & A. Gray var. lonchophyllum
- Spearleaf Buckwheat - Eriogonum Lonchophyllum Torr. & A. Gray var. nudicaule (Torr.) Reveal
- Spearleaf - Matelea Parvifolia (Torr.) Woodson
- Spearleaf Rabbitbrush - Chrysothamnus Linifolius Greene
- Spearleaf Stonecrop - Sedum Lanceolatum Torr.
- Spearleaf Stonecrop - Sedum Lanceolatum Torr. ssp. lanceolatum
- Spearleaf Stonecrop - Sedum Lanceolatum Torr. ssp. nesioticum (G.N. Jones) R.T. Clausen
- Spearleaf Swampmallow - Pavonia Hastata Cav.
- Spearmint - Mentha Spicata L.
- Spearshaped Phacelia - Phacelia Hastata Douglas ex Lehm. var. dasyphylla (Greene ex J.F. Macbr.) Kartesz
- Spearwood - Acacia Doratoxylon A. Cunn.
- Speckled Alder - Alnus Incana (L.) Moench ssp. rugosa (Du Roi) R.T. Clausen
- Speckled Clarkia - Clarkia Cylindrica (Jeps.) F.H. Lewis & M.E. Lewis
- Speckled Clarkia - Clarkia Cylindrica (Jeps.) F.H. Lewis & M.E. Lewis ssp. clavicarpa W.S. Davis
- Speckled Clarkia - Clarkia Cylindrica (Jeps.) F.H. Lewis & M.E. Lewis ssp. cylindrica
- Speckled False Dandelion - Nothocalais Nigrescens (L.F. Hend.) A. Heller
- Speckled Spur Flower - Plectranthus Ciliatus E. Mey.
- Spectacle Fruit - Wislizenia Refracta Engelm.
- Spectacle Fruit - Wislizenia Refracta Engelm. ssp. californica (Greene) Keller
- Spectacle Fruit - Wislizenia Refracta Engelm. ssp. refracta
- Spectaclepod - Dimorphocarpa Rollins
- Spectacular Flatsedge - Cyperus Manimae Kunth
- Spectacular Flatsedge - Cyperus Manimae Kunth var. asperrimus (Liebm.) Kük.
- Spectacular Flatsedge - Cyperus Spectabilis Link
- Specularia Biflora (Ruiz & Pav.) Fisch. & C.A. Mey.
- Specularia Holzingeri (McVaugh) Fernald
- Specularia Lamprosperma (McVaugh) Fernald
- Specularia Leptocarpa (Nutt.) A. Gray
- Specularia Perfoliata (L.) A. DC.
- Specularia Rariflora (Nutt.) McVaugh
- Specularia Speculum-veneris (L.) Tanfani
- Speedwell - Pseudolysimachion (w.d.j. Koch) Opiz
- Speedwell - Veronica L.
- Speenwort - Asplenium Caudatum G. Forst.
- Speerschneidera Lichen - Speerschneidera Euploca (Tuck.) Trevis.
- Speerschneidera Lichen - Speerschneidera Trevis.
- Spellenberg's Springparsley - Cymopterus Spellenbergii R.L. Hartm. & J.E. Larson
- Spelt - Triticum Spelta L.
- Spergella Caespitosa (J. Vahl) Á. Löve & D. Löve
- Spergella Intermedia (Fenzl) Á. Löve & D. Löve
- Spergella Nodosa (L.) Rchb.
- Spergella Saginoides (L.) Rchb.
- Spergula Arvensis L. ssp. arvensis
- Spergula Arvensis L. ssp. sativa (Boenn.) Celak.
- Spergula Arvensis L. var. sativa (Boenn.) Mert. & W.D.J. Koch
- Spergula Sativa Boenn.
- Spergularia Alata Wiegand
- Spergularia Bocconi (Scheele) Graebn.
- Spergularia Clevelandii (Greene) B.L. Rob.
- Spergularia Leiosperma (Kindb.) F. Schmidt
- Spergularia Marginata (DC.) Kittel
- Spergularia Marina (L.) Griseb.
- Spergularia Marina (L.) Griseb. var. leiosperma (Kindb.) Guerke
- Spergularia Marina (L.) Griseb. var. simonii O. Deg. & I. Deg.
- Spergularia Marina (L.) Griseb. var. tenuis (Greene) R.P. Rossb.
- Spergularia Media (L.) C. Presl ex Griseb.
- Spergularia Rubra (L.) J. Presl & C. Presl var. perennans (Kindb.) B.L. Rob.
- Spergularia Salina J. Presl & C. Presl var. tenuis (Greene) Jeps.
- Spergularia Salsuginea (Bunge) Fenzl
- Spergularia Salsuginea (Bunge) Fenzl var. bracteata B.L. Rob.
- Spergularia Sparsiflora (Greene) A. Nelson
- Spergularia Tenuis (Greene) B.L. Rob. var. involucrata B.L. Rob.
- Spergulastrum Lanceolatum Michx.
- Spergulastrum Lanuginosum Michx.
- Spergulastrum Lanuginosum Michx. ssp. saxosum (A. Gray) W.A. Weber
- Spermacoce Ernstii Fosberg & Powell
- Spermacoce Hirta L.
- Spermacoce Keyensis Small
- Spermacoce Mauritiana auct. non Gideon
- Spermacoce Ocymoides auct. non Burm. f.
- Spermacoce Remota Lam.
- Spermacoce Repens auct. non (DC.) Sessé & Moc.
- Spermacoce Riparia Cham. & Schltdl.
- Spermacoce Riparia auct. non Cham. & Schltdl.
- Spermacoce Serrulata P. Beauv.
- Spermacoce Suffrutescens Jacq.
- Spermacoce Tenella Kunth [excluded]
- Spermacoce Tenuior L. var. floridana (Urb.) R.W. Long
- Spermacoce Tenuior auct. non L.
- Spermolepis Patens (Nutt. ex DC.) B.L. Rob.
- Sperry Guava - Eugenia Corozalensis Britton
- Sperry's Milkweed - Asclepias Sperryi Woodson
- Sperry's Onion - Allium Perdulce S.V. Fraser var. sperryi Ownbey
- Sphaeralcea Ambigua A. Gray var. aculeata Jeps.
- Sphaeralcea Ambigua A. Gray var. ambigua
- Sphaeralcea Ambigua A. Gray var. rosacea (Munz & I.M. Johnst.) Kearney
- Sphaeralcea Ambigua A. Gray var. rugosa (Kearney) Kearney
- Sphaeralcea Angusta (A. Gray) Fernald
- Sphaeralcea Angustifolia (Cav.) G. Don ssp. cuspidata (A. Gray) Kearney
- Sphaeralcea Angustifolia (Cav.) G. Don ssp. lobata (Wooton) Kearney
- Sphaeralcea Angustifolia (Cav.) G. Don var. cuspidata A. Gray
- Sphaeralcea Angustifolia (Cav.) G. Don var. lobata (Wooton) Kearney
- Sphaeralcea Angustifolia (Cav.) G. Don var. oblongifolia (A. Gray) Shinners
- Sphaeralcea Cisplatina A. St.-Hil.
- Sphaeralcea Coccinea (Nutt.) Rydb. ssp. dissecta (Nutt. ex Torr. & A. Gray) Kearney
- Sphaeralcea Coccinea (Nutt.) Rydb. var. dissecta (Nutt. ex Torr. & A. Gray) Garrett
- Sphaeralcea Coccinea (Nutt.) Rydb. var. elata (Baker f.) Kearney
- Sphaeralcea Cuspidata (A. Gray) Britton
- Sphaeralcea Digitata (Greene) Rydb. var. angustiloba (A. Gray) Shinners
- Sphaeralcea Digitata (Greene) Rydb. var. tenuipes (Wooton & Standl.) Kearney
- Sphaeralcea Emoryi Torr. ex A. Gray ssp. arida (Rose) Kearney
- Sphaeralcea Emoryi Torr. ex A. Gray ssp. nevadensis Kearney
- Sphaeralcea Emoryi Torr. ex A. Gray ssp. variabilis (Cockerell) Kearney
- Sphaeralcea Emoryi Torr. ex A. Gray var. arida (Rose) Kearney
- Sphaeralcea Emoryi Torr. ex A. Gray var. californica (Parish) Shinners
- Sphaeralcea Emoryi Torr. ex A. Gray var. emoryi
- Sphaeralcea Emoryi Torr. ex A. Gray var. nevadensis (Kearney) Kearney
- Sphaeralcea Emoryi Torr. ex A. Gray var. variabilis (Cockerell) Kearney
- Sphaeralcea Eremicola Jeps.
- Sphaeralcea Fendleri A. Gray var. albescens (Kearney) Kearney
- Sphaeralcea Fendleri A. Gray var. elongata (Kearney) Kearney
- Sphaeralcea Fendleri A. Gray var. tripartita (Wooton & Standl.) Kearney
- Sphaeralcea Fendleri A. Gray var. venusta (Kearney) Kearney
- Sphaeralcea Grossulariifolia (Hook. & Arn.) Rydb. var. fumariensis S.L. Welsh & N.D. Atwood
- Sphaeralcea Grossulariifolia (Hook. & Arn.) Rydb. var. moorei S.L. Welsh
- Sphaeralcea Grossulariifolia (Hook. & Arn.) Rydb. var. pedata (Torr. ex A. Gray) Kearney
- Sphaeralcea Incana Torr. ex A. Gray var. cuneata (Kearney) Kearney
- Sphaeralcea Leptophylla (A. Gray) Rydb. var. janeae S.L. Welsh
- Sphaeralcea Miniata Spach
- Sphaeralcea Munroana (Douglas) Spach var. subrhomboidea (Rydb.) Kearney
- Sphaeralcea Rivularis (Douglas ex Hook.) Torr.
- Sphaeralcea Rusbyi A. Gray var. eremicola (Jeps.) Kearney
- Sphaeralcea Rusbyi A. Gray var. gilensis (Kearney) Kearney
- Sphaeralcea Subhastata J.M. Coult.
- Sphaeralcea Subhastata J.M. Coult. ssp. connata Kearney
- Sphaeralcea Subhastata J.M. Coult. ssp. latifolia Kearney
- Sphaeralcea Subhastata J.M. Coult. ssp. martii (Cockerell) Kearney
- Sphaeralcea Subhastata J.M. Coult. ssp. pumila (Wooton & Standl.) Kearney
- Sphaeralcea Subhastata J.M. Coult. ssp. thyrsoidea Kearney
- Sphaeralcea Subhastata J.M. Coult. var. connata (Kearney) Kearney
- Sphaeralcea Subhastata J.M. Coult. var. latifolia (Kearney) Kearney
- Sphaeralcea Subhastata J.M. Coult. var. martii (Cockerell) Kearney
- Sphaeralcea Subhastata J.M. Coult. var. pumila (Wooton & Standl.) Kearney
- Sphaeralcea Subhastata J.M. Coult. var. thyrsoidea (Kearney) Kearney
- Sphaeralcea Umbellata (Cav.) G. Don
- Sphaerellothecium Abditum Triebel
- Sphaerellothecium Araneosum (Rehm ex Arnold) Zopf
- Sphaerellothecium Lichen - Sphaerellothecium Contextum Triebel
- Sphaerellothecium Lichen - Sphaerellothecium Zopf
- Sphaerellothecium Minutum Hafellner
- Sphaeria Bignoniae Schwein.
- Sphaerocarpos Boehm.
- Sphaerocarpos Cristatus M. Howe
- Sphaerocarpos Donnellii Austin
- Sphaerocarpos Drewei Wigglesworth
- Sphaerocarpos Hians Haynes
- Sphaerocarpos Michelii Bellardi
- Sphaerocarpos Texanus Austin
- Sphaerocionium Lanceolatum (Hook. & Arn.) Copeland
- Sphaeromeria Potentilloides (A. Gray) A. Heller
- Sphaeromeria Potentilloides (A. Gray) A. Heller var. nitrophila (Cronquist) A.H. Holmgren, L
- Sphaeromeria Potentilloides (A. Gray) A. Heller var. potentilloides
- Sphaerophorus Melanocarpus (Sw.) DC.
- Sphaerophorus Tuckermanii Rasanen
- Sphaerophysa - Sphaerophysa Dc.
- Sphaeropteris Cooperi (Hook. ex F. Muell.) R. Tryon
- Sphaeropteris Lunulata (G. Forst.) R.M. Tryon
- Sphaeropteris Nigricans (Mett.) R.M. Tryon
- Sphaerosporoceros Adscendens (Lehm. & Lindenb.) Hässel
- Sphaerostephanos Heterocarpus (Blume) Holttum
- Sphaerostephanos Invisus (G. Forst.) Holttum
- Sphaerostephanos J. Sm.
- Sphaerostephanos Maemonensis (W.H. Wagner & Grether) Holttum
- Sphaerostephanos Perglanduliferus (Alderw.) Holttum
- Sphaerostephanos Taiwanensis (C. Chr.) Holttum ex C.M. Kuo
- Sphaerostephanos Unitus (L.) Holttum
- Sphaerostigma Hallii Davidson
- Sphaerostigma Minor A. Nelson
- Sphaerostigma Pallida Abrams
- Sphaerostigma Strigulosa Fisch. & C.A. Mey.
- Sphaerulina Dolichotera (Nyl.) Vouax
- Sphaerulina Sacc.
- Sphagnum Absonditella Lichen - Absconditella Sphagnorum Vezda & Poelt
- Sphagnum Acutifolium Ehrh. ex Schrad.
- Sphagnum Amblyphyllum (Russow) Zick.
- Sphagnum Annulatum H. Lindb. ex Warnst. var. porosum (Schlieph. & Warnst.) Maass &
- Sphagnum Apiculatum H. Lindb.
- Sphagnum Auriculatum Schimp.
- Sphagnum Auriculatum Schimp. var. inundatum (Russow) M.O. Hill
- Sphagnum Blackberry - Rubus Spectatus L.H. Bailey
- Sphagnum Capillaceum (Weiss.) Schrank
- Sphagnum Capillaceum (Weiss.) Schrank var. tenellum (Schimp.) Andrews
- Sphagnum Capillaceum (Weiss.) Schrank var. tenerum (Sull. & Lesq.) Andrews
- Sphagnum Capillifolium (Ehrh.) Hedw. var. tenellum (Schimp.) H.A. Crum
- Sphagnum Capillifolium (Ehrh.) Hedw. var. tenerum (Sull. & Lesq.) H.A. Crum
- Sphagnum Carlottae R.E. Andrus
- Sphagnum Compactum DC. var. expositum Maass
- Sphagnum Cribrosum Lindb.
- Sphagnum Crispum R.E. Andrus
- Sphagnum Cuspidatum Ehrh. ex Hoffm. var. dusenii C.E.O. Jensen ex Warnst.
- Sphagnum Cuspidatum Ehrh. ex Hoffm. var. plumosum Nees & Hornsch.
- Sphagnum Cuspidatum Ehrh. ex Hoffm. var. serrulatum (Schlieph.) Schlieph.
- Sphagnum Cuspidatum Ehrh. ex Hoffm. var. torreyanum (Sull.) Lesq. & James
- Sphagnum Cuspidatum Ehrh. ex Hoffm. var. torreyi Braithw.
- Sphagnum Dewberry - Rubus Signatus L.H. Bailey
- Sphagnum Dusenii (C.E.O. Jensen ex Warnst.) Russow & Warnst.
- Sphagnum Erythrocalyx sensu Andrews
- Sphagnum Fallax (Klinggr.) Klinggr. var. angustifolium (C.E.O. Jensen ex Russow)
- Sphagnum Fimbriatum Wilson var. arcticum C.E.O. Jensen
- Sphagnum Fimbriatum Wilson var. tenue Grav. ex Röll
- Sphagnum Flexuosum Dozy & Molk. var. fallax (Klinggr.) M.O. Hill ex A.J.E. Sm.
- Sphagnum Flexuosum Dozy & Molk. var. tenue (Klinggr.) Pilous
- Sphagnum Floridanum (Austin) Cardot
- Sphagnum Garberi Lesq. & James
- Sphagnum Imbricatum Hornsch. ex Russow ssp. affine (Renauld & Cardot) Flatberg
- Sphagnum Imbricatum Hornsch. ex Russow ssp. austinii (Sull.) Flatberg
- Sphagnum Imbricatum Hornsch. ex Russow var. affine (Renauld & Cardot) Warnst.
- Sphagnum Imbricatum Hornsch. ex Russow var. arcticum Flatberg
- Sphagnum Imbricatum Hornsch. ex Russow var. flagellare Flatberg
- Sphagnum Jensenii H. Lindb. var. annulatum (H. Lindb. ex Warnst.) Warnst.
- Sphagnum Junghuhnianum Dozy & Molk. ssp. pseudomolle (Warnst.) Suz.
- Sphagnum Lindbergii Schimp. ssp. lenense (H. Lindb.) Podp.
- Sphagnum Lindbergii Schimp. var. microphyllum Warnst.
- Sphagnum Majus (Russow) C.E.O. Jensen ssp. norvegica Flatberg, orth. var.
- Sphagnum Nemoreum Scop. var. subtile Russow
- Sphagnum Nemoreum Scop. var. tenerum (Sull. & Lesq.) Nyholm
- Sphagnum Nemoreum Scop., nom. dub.
- Sphagnum Obesum (Wilson) Warnst.
- Sphagnum Obtusum Warnst. var. dusenii C.E.O. Jensen ex Warnst.
- Sphagnum Papillosum Lindb. var. laeve Warnst.
- Sphagnum Papillosum Lindb. var. sublaeve Warnst.
- Sphagnum Parvifolium (Sendtn. ex Warnst.) Warnst.
- Sphagnum Perfoliatum Sav.-Ljub.
- Sphagnum Plumulosum Röll
- Sphagnum Pulchricoma Müll. Hal.
- Sphagnum Pylaesii Brid. var. sedoides (Brid.) Lindb.
- Sphagnum Recurvum P. Beauv. ssp. angustifolium C.E.O. Jensen ex Russow
- Sphagnum Recurvum P. Beauv. var. amblyphyllum (Russow) Warnst.
- Sphagnum Recurvum P. Beauv. var. brevifolium (Lindb. ex Braithw.) Warnst.
- Sphagnum Recurvum P. Beauv. var. fallax (Klinggr.) Paul
- Sphagnum Recurvum P. Beauv. var. parvifolium Sendtn. ex Warnst.
- Sphagnum Recurvum P. Beauv. var. porosum Schlieph. & Warnst.
- Sphagnum Recurvum P. Beauv. var. tenue Klinggr.
- Sphagnum Robustum (Warnst.) Röll
- Sphagnum Rufescens Nees & Hornsch.
- Sphagnum Sedoides Brid.
- Sphagnum Serratum Austin
- Sphagnum - Sphagnum Affine Renauld & Cardot
- Sphagnum - Sphagnum Angustifolium (C.E.O. Jensen ex Russow) C.E.O. Jensen
- Sphagnum - Sphagnum Annulatum H. Lindb. ex Warnst.
- Sphagnum - Sphagnum Capillifolium (Ehrh.) Hedw.
- Sphagnum - Sphagnum Centrale C.E.O. Jensen
- Sphagnum - Sphagnum Cyclophyllum Sull. & Lesq.
- Sphagnum - Sphagnum Denticulatum Brid.
- Sphagnum - Sphagnum Fallax (Klinggr.) Klinggr.
- Sphagnum - Sphagnum Fimbriatum Wilson
- Sphagnum - Sphagnum Fimbriatum Wilson var. concinnum (Berggr.) Warnst.
- Sphagnum - Sphagnum Fimbriatum Wilson var. fimbriatum
- Sphagnum - Sphagnum Flavicomans (Cardot) Warnst.
- Sphagnum - Sphagnum Flexuosum Dozy & Molk.
- Sphagnum - Sphagnum Flexuosum Dozy & Molk. var. flexuosum
- Sphagnum - Sphagnum Flexuosum Dozy & Molk. var. ramosissimum R.E. Andrus
- Sphagnum - Sphagnum Fuscum (Schimp.) Klinggr.
- Sphagnum - Sphagnum L.
- Sphagnum - Sphagnum Lenense H. Lindb.
- Sphagnum - Sphagnum Majus (Russow) C.E.O. Jensen
- Sphagnum - Sphagnum Majus (Russow) C.E.O. Jensen ssp. norvegica Flatberg
- Sphagnum - Sphagnum Majus (Russow) C.E.O. Jensen ssp. norvegicum Flatberg
- Sphagnum - Sphagnum Molle Sull.
- Sphagnum - Sphagnum Nitidum Warnst.
- Sphagnum - Sphagnum Obtusum Warnst.
- Sphagnum - Sphagnum Perichaetiale Hampe
- Sphagnum - Sphagnum Platyphyllum (Lindb. ex Braithw.) Sull. ex Warnst.
- Sphagnum - Sphagnum Pulchrum (Lindb. ex Braithw.) Warnst.
- Sphagnum - Sphagnum Quinquefarium (Lindb. ex Braithw.) Warnst.
- Sphagnum - Sphagnum Rubellum Wilson
- Sphagnum - Sphagnum Rubroflexuosum R.E. Andrus
- Sphagnum - Sphagnum Splendens Maass
- Sphagnum - Sphagnum Squarrosum Crome
- Sphagnum - Sphagnum Strictum Sull.
- Sphagnum - Sphagnum Subnitens Russow & Warnst.
- Sphagnum - Sphagnum Subobesum Warnst.
- Sphagnum - Sphagnum Subsecundum Nees
- Sphagnum - Sphagnum Subsecundum Nees var. subsecundum
- Sphagnum - Sphagnum Subtile (Russow) Warnst.
- Sphagnum - Sphagnum Tenellum (Brid.) Bory
- Sphagnum - Sphagnum Tenerum Sull. & Lesq.
- Sphagnum - Sphagnum Teres (Schimp.) Ångstr.
- Sphagnum - Sphagnum Viridum Flatberg
- Sphagnum Subfulvum Sjors
- Sphagnum Subsecundum Nees var. carolinianum (R.E. Andrus) H.A. Crum
- Sphagnum Subsecundum Nees var. contortum (Schultz) Hüb.
- Sphagnum Subsecundum Nees var. inundatum (Russow) C.E.O. Jensen
- Sphagnum Subsecundum Nees var. junsaiense (Warnst.) H.A. Crum
- Sphagnum Subsecundum Nees var. platyphyllum (Lindb. ex Braithw.) Cardot
- Sphagnum Subsecundum Nees var. rufescens (Nees & Hornsch.) Hüb.
- Sphagnum Tabulare Sull.
- Sphagnum Warnstorfianum Du Rietz
- Sphenoclea - Sphenoclea Gaertn.
- Sphenolobopsis Pearsonii (Spruce) R.M. Schust.
- Sphenolobopsis R.m. Schust. & N. Kitag.
- Sphenomeris Chinensis (L.) Maxon
- Sphenomeris Chinensis (L.) Maxon ssp. biflora (Kaulf.) Jôtani & Ohba
- Sphenomeris Chusiana (L.) Copeland
- Sphenomeris Clavata (L.) Maxon
- Sphenopholis Intermedia (Rydb.) Rydb. var. pilosa Dore
- Sphenopholis Obtusata (Michx.) Scribn. var. lobata (Trin.) Scribn.
- Sphenopholis Obtusata (Michx.) Scribn. var. major (Torr.) K.S. Erdman
- Sphenopholis Obtusata (Michx.) Scribn. var. pubescens (Scribn. & Merr.) Scribn.
- Sphenosciadium - Sphenosciadium A. Gray
- Sphenostigma Coelestinum (W. Bartram) R.C. Foster
- Sphenostylis - Sphenostylis E. Meyer
- Spherical Blazing Star - Liatris Spheroidea Michx.
- Sphinctospermum - Sphinctospermum Rose
- Sphinctrina Lichen - Sphinctrina Anglica Nyl.
- Sphinctrina Lichen - Sphinctrina Fr.
- Sphinctrina Lichen - Sphinctrina Leucopoda Nyl.
- Sphinctrina Lichen - Sphinctrina Tubiformis A. Massal.
- Sphinctrina Lichen - Sphinctrina Turbinata (Pers. ex Fr.) De Not.
- Sphinctrina Microcephala (Sm.) Körb.
- Sphinctrina Microcephala Nyl.
- Sphinctrinella Calicioides Nadv.
- Spice Lily - Manfreda Maculosa (Hook.) Rose
- Spicebush - Lindera Thunb.
- Spider Biscuitroot - Lomatium Tarantuloides Darrach & Hinchliff
- Spider Brake - Pteris Multifida Poir.
- Spider Lupine - Lupinus Benthamii A. Heller
- Spider Lupine - Lupinus Benthamii A. Heller var. benthamii
- Spider Lupine - Lupinus Benthamii A. Heller var. opimus C.P. Sm.
- Spider Milkweed - Asclepias Asperula (Decne.) Woodson
- Spider Milkweed - Asclepias Asperula (Decne.) Woodson ssp. asperula
- Spider Plant - Chlorophytum Comosum (Thunb.) Jacq.
- Spiderflower - Cleome L.
- Spidergrass - Aristida Ternipes Cav.
- Spidergrass - Aristida Ternipes Cav. var. gentilis (Henr.) Allred
- Spidergrass - Aristida Ternipes Cav. var. ternipes
- Spiderleaf - Ipomoea Tenuiloba Torr.
- Spiderleaf - Ipomoea Tenuiloba Torr. var. lemmonii (A. Gray) Yatsk. & C.T. Mason
- Spiderleaf - Ipomoea Tenuiloba Torr. var. tenuiloba
- Spiderlily - Hymenocallis Salisb.
- Spiderling - Boerhavia L.
- Spiderweb Chloris - Chloris Pycnothrix Trin.
- Spiderwisp - Cleome Gynandra L.
- Spiderwort - Tradescantia L.
- Spiderwort - Tradescantia ×andersoniana W. Ludwig & Rohweder
- Spiesia Lagopus (Nutt.) Kuntze
- Spiesia Oreophila (A. Gray) Kuntze
- Spigelia Gentianoides Chapm. ex A. DC. var. alabamensis K. Gould
- Spigelia Gentianoides auct. non Chapm. ex A. DC.
- Spigelia Lindheimeri A. Gray
- Spike Bentgrass - Agrostis Exarata Trin.
- Spike Dropseed - Sporobolus Contractus Hitchc.
- Spike Fescue - Leucopoa Griseb.
- Spike Fescue - Leucopoa Kingii (S. Watson) W.A. Weber
- Spike Lichen - Calicium Abietinum Pers.
- Spike Lichen - Calicium Adspersum Pers.
- Spike Lichen - Calicium Chlorosporum F. Wilson
- Spike Lichen - Calicium Corynellum (Ach.) Ach.
- Spike Lichen - Calicium Glaucellum Ach.
- Spike Lichen - Calicium Hyperelloides Nyl.
- Spike Lichen - Calicium Lenticulare Ach.
- Spike Lichen - Calicium Leucochlorum Tuck.
- Spike Lichen - Calicium Parvum Tibell
- Spike Lichen - Calicium Pers.
- Spike Lichen - Calicium Quercinum Pers.
- Spike Lichen - Calicium Salicinum Pers.
- Spike Lichen - Calicium Trabinellum (Ach.) Ach.
- Spike Lichen - Calicium Viride Pers.
- Spike Lovegrass - Eragrostis Spicata Vasey
- Spike Muhly - Muhlenbergia Wrightii Vasey ex J.M. Coult.
- Spike Quillwort - Isoetes Prototypus D.M. Britton
- Spike Sedge - Carex Nardina Fr.
- Spike Sedge - Carex Nardina Fr. var. nardina
- Spike Trisetum - Trisetum Spicatum (L.) K. Richt.
- Spiked Beaksedge - Rhynchospora Chinensis Nees & Meyen
- Spiked Beaksedge - Rhynchospora Chinensis Nees & Meyen ssp. chinensis
- Spiked Beaksedge - Rhynchospora Chinensis Nees & Meyen ssp. spiciformis (Hillebr.) T. Koyama
- Spiked Broomrape - Orobanche Multicaulis Brandegee
- Spiked Bur Grass - Tragus Berteronianus Schult.
- Spiked Centaury - Centaurium Spicatum (L.) Fritsch
- Spiked Crested Coralroot - Hexalectris Arizonica (S.Watson) A.H. Kenn. & L.E. Watson
- Spiked Crested Coralroot - Hexalectris Spicata (Walter) Barnhart
- Spiked Crested Coralroot - Hexalectris Spicata (Walter) Barnhart var. spicata
- Spiked Crinkleawn - Trachypogon Spicatus (L. f.) Kuntze
- Spiked False Mannagrass - Torreyochloa Erecta (Hitchc.) Church
- Spiked Hoarypea - Tephrosia Spicata (Walter) Torr. & A. Gray
- Spiked Ipomopsis - Ipomopsis Spicata (Nutt.) V.E. Grant
- Spiked Ipomopsis - Ipomopsis Spicata (Nutt.) V.E. Grant ssp. capitata (A. Gray) V.E. Grant
- Spiked Ipomopsis - Ipomopsis Spicata (Nutt.) V.E. Grant ssp. robruthii Wilken & R.L. Hartm.
- Spiked Ipomopsis - Ipomopsis Spicata (Nutt.) V.E. Grant ssp. spicata
- Spiked Ipomopsis - Ipomopsis Spicata (Nutt.) V.E. Grant ssp. tridactyla (Rydb.) Wilken & R.L. Hartm.
- Spiked Larkspur - Delphinium Stachydeum (A. Gray) Tidestr.
- Spiked Manihot - Manihot Subspicata D.J. Rogers & Appan
- Spiked Muhly - Muhlenbergia Glomerata (Willd.) Trin.
- Spiked Saxifrage - Saxifraga Spicata D. Don
- Spiked Speedwell - Veronica Spicata L.
- Spiked Speedwell - Veronica Spicata L. ssp. incana (L.) Walters
- Spiked Speedwell - Veronica Spicata L. ssp. spicata
- Spiked Spiralflag - Costus Spicatus (Jacq.) Sw.
- Spiked Ticktrefoil - Desmodium Cinerascens A. Gray
- Spiked Western Rosinweed - Calycadenia Spicata (Greene) Greene
- Spiked Wild Indigo - Baptisia Albescens Small
- Spiked Woodrush - Luzula Spicata (L.) DC.
- Spikemoss - Selaginella P. Beauv.
- Spikemoss - Selaginella Pseudovolkensii Hosok.
- Spikemoss - Selaginella Umbrosa Lem. ex Hieron.
- Spikenard - Aralia L.
- Spikeoat - Avenula Hookeri (Scribn.) Holub
- Spikerush - Eleocharis Congesta D. Don
- Spikerush - Eleocharis Obtusetrigona (Lindl. & Nees) Steud.
- Spikerush - Eleocharis Ochrostachys Steud.
- Spikerush - Eleocharis R. Br.
- Spikesedge - Kyllinga Rottb.
- Spiky Mother-in-law's Tongue - Sansevieria Pearsonii N.E. Br.
- Spilanthes Americana (Mutis ex L. f.) Hieron. var. repens (Walter) A.H. Moore
- Spilanthes Americana (Mutis ex L. f.) Hieron. var. stolonifera (DC.) A.H. Moore
- Spilanthes Americana auct. non Hieron. p.p.
- Spilanthes Iodiscaea A.H. Moore
- Spilanthes Pusilla Hook. & Arn.
- Spilanthes - Spilanthes Jacq.
- Spilanthes - Spilanthes Oleracea L.
- Spilanthes Stolonifera DC.
- Spilanthes Uliginosa Sw.
- Spilonema Lichen - Spilonema Bornet
- Spilonema Lichen - Spilonema Revertens Nyl.
- Spinach - Spinacia L.
- Spinach - Spinacia Oleracea L.
- Spindle Tree - Euonymus Patens Rehder
- Spindleroot - Ludwigia Hirtella Raf.
- Spindletree - Euonymus L.
- Spine Acanthus - Acanthus Spinosus L.
- Spinecape - Goodmania Reveal & Ertter
- Spineflower - Chorizanthe R. Br. ex Benth.
- Spineflower - Dodecahema Reveal & Hardham
- Spineflower - Mucronea Benth.
- Spineflower - Systenotheca Reveal & Hardham
- Spineless Hornwort - Ceratophyllum Echinatum A. Gray
- Spineless Horsebrush - Tetradymia Canescens DC.
- Spineless Wattle - Senegalia Muricata (L.) Britton & Rose
- Spinescale Saltbush - Atriplex Spinifera J.F. Macbr.
- Spinifex L.
- Spinning Gum - Eucalyptus Perriniana F. Muell. ex Rodway
- Spinster's Blue Eyed Mary - Collinsia Sparsiflora Fisch. & C.A. Mey.
- Spinster's Blue Eyed Mary - Collinsia Sparsiflora Fisch. & C.A. Mey. var. arvensis (Greene) Jeps.
- Spinster's Blue Eyed Mary - Collinsia Sparsiflora Fisch. & C.A. Mey. var. bruceae (M.E. Jones) Newsom
- Spinster's Blue Eyed Mary - Collinsia Sparsiflora Fisch. & C.A. Mey. var. collina (Jeps.) Newsom
- Spinster's Blue Eyed Mary - Collinsia Sparsiflora Fisch. & C.A. Mey. var. sparsiflora
- Spinulose Woodfern - Dryopteris Carthusiana (Vill.) H.P. Fuchs
- Spinulum Annotinum (L.) A. Haines
- Spiny Amaranth - Amaranthus Spinosus L.
- Spiny Bucida - Bucida Molinetii (G. Maza) Alain
- Spiny Calcareous Moss - Mnium Spinosum (Voit) Schwägr.
- Spiny Caper - Oxystylis Lutea Torr. & Frém.
- Spiny Chloracantha - Chloracantha Spinosa (Benth.) G.L. Nesom
- Spiny Cliffbrake - Pellaea Truncata Goodding
- Spiny Cocklebur - Xanthium Spinosum L.
- Spiny Combretum - Combretum Obovatum F. Hoffm.
- Spiny False Fiddleleaf - Hydrolea Spinosa L.
- Spiny Fameflower - Phemeranthus Spinescens (Torr.) Hershkovitz
- Spiny Fiddlewood - Citharexylum Spinosum L.
- Spiny Greasebush - Glossopetalon Spinescens A. Gray
- Spiny Greasebush - Glossopetalon Spinescens A. Gray var. aridum M.E. Jones
- Spiny Greasebush - Glossopetalon Spinescens A. Gray var. meionandrum (Koehne) Trel.
- Spiny Greasebush - Glossopetalon Spinescens A. Gray var. microphyllum N.H. Holmgren
- Spiny Greasebush - Glossopetalon Spinescens A. Gray var. spinescens
- Spiny Hackberry - Celtis Ehrenbergiana (Klotzsch) Liebm.
- Spiny Hedgehog Cactus - Echinocereus Dasyacanthus Engelm.
- Spiny Holdback - Caesalpinia Spinosa (Molina) Kuntze
- Spiny Hopsage - Grayia Spinosa (Hook.) Moq.
- Spiny Kidneywood - Eysenhardtia Spinosa Engelm.
- Spiny Logwood - Xylosma Pachyphylla (Krug & Urb.) Urb.
- Spiny Menodora - Menodora Spinescens A. Gray
- Spiny Milkvetch - Astragalus Kentrophyta A. Gray
- Spiny Milkvetch - Astragalus Kentrophyta A. Gray var. danaus (Barneby) Barneby
- Spiny Milkvetch - Astragalus Kentrophyta A. Gray var. jessiae (M. Peck) Barneby
- Spiny Milkvetch - Astragalus Kentrophyta A. Gray var. kentrophyta
- Spiny Milkvetch - Astragalus Kentrophyta A. Gray var. ungulatus M.E. Jones
- Spiny Milkwort - Polygala Subspinosa S. Watson
- Spiny Naiad - Najas Marina L.
- Spiny Phlox - Phlox Hoodii Richardson
- Spiny Phlox - Phlox Hoodii Richardson ssp. hoodii
- Spiny Plumeless Thistle - Carduus Acanthoides L.
- Spiny Restharrow - Ononis Spinosa L.
- Spiny Rush - Juncus Acutus L.
- Spiny Sowthistle - Sonchus Asper (L.) Hill
- Spiny Spiderflower - Cleome Spinosa Jacq.
- Spiny Spikemoss - Selaginella Acanthonota Underw.
- Spiny Threecornerjack - Emex Spinosa (L.) Campd.
- Spiny Treefern - Cyathea Pungens (Willd.) Domin
- Spiny-spore Quillwort - Isoetes Tenella Léman
- Spinycape - Aristocapsa Reveal & Hardham
- Spinyfruit Buttercup - Ranunculus Muricatus L.
- Spinyfruit Raspwort - Gonocarpus Acanthocarpus (Brongn.) Orchard
- Spinyhair Blazingstar - Mentzelia Tricuspis A. Gray
- Spinysepal Eryngo - Eryngium Spinosepalum Mathias
- Spinystar - Escobaria Vivipara (Nutt.) Buxbaum
- Spinystar - Escobaria Vivipara (Nutt.) Buxbaum var. buoflama (P.C. Fisch.) N.P. Taylor
- Spinystar - Escobaria Vivipara (Nutt.) Buxbaum var. radiosa (Engelm.) D.R. Hunt
- Spinystar - Escobaria Vivipara (Nutt.) Buxbaum var. rosea (Clokey) D.R. Hunt
- Spinystar - Escobaria Vivipara (Nutt.) Buxbaum var. vivipara
- Spinytooth Clover - Trifolium Mucronatum Willd. ex Spreng. ssp. lacerum (Greene) J.M. Gillett
- Spiraea Alba Du Roi var. septentrionalis (Fernald) Seymour
- Spiraea Albiflora (Miq.) Zabel
- Spiraea Arbuscula Greene
- Spiraea Aruncus L.
- Spiraea Beauverdiana C.K. Schneid. var. stevenii C.K. Schneid.
- Spiraea Beauverdiana auct. non C.K. Schneid.
- Spiraea Betulifolia Pall. ssp. corymbosa (Raf.) Roy L. Taylor & MacBryde
- Spiraea Betulifolia Pall. ssp. lucida (Douglas ex Greene) Roy L. Taylor & MacBryde
- Spiraea Betulifolia Pall. var. corymbosa (Raf.) Maxim.
- Spiraea Betulifolia Pall. var. lucida (Douglas ex Greene) C.L. Hitchc.
- Spiraea Betulifolia Pall. var. rosea A. Gray
- Spiraea Bullata Maxim.
- Spiraea Caespitosa Nutt.
- Spiraea Californica Torr.
- Spiraea Densiflora Nutt. ex Greenm.
- Spiraea Densiflora Nutt. ex Greenm. ssp. splendens (Baumann ex K. Koch) Abrams
- Spiraea Densiflora Nutt. ex Greenm. var. splendens (Baumann ex K. Koch) C.L. Hitchc
- Spiraea Discolor Pursh
- Spiraea Douglasii Hook. ssp. menziesii (Hook.) Calder & Roy L. Taylor
- Spiraea Douglasii Hook. var. roseata (Rydb.) C.L. Hitchc.
- Spiraea Flexuosa Fisch. ex Cambess.
- Spiraea Gemmata Zabel
- Spiraea Hendersonii (Canby) Piper
- Spiraea Japonica L. f. var. alpina Maxim.
- Spiraea Japonica L. f. var. bullata (Maxim.) Makino
- Spiraea Latifolia (Aiton) Borkh.
- Spiraea Latifolia (Aiton) Borkh. var. septentrionalis Fernald
- Spiraea Media Schmidt
- Spiraea Menziesii Hook.
- Spiraea Nipponica Maxim.
- Spiraea Nipponica Maxim. f. rotundifolia (G. Nicholson) Makino
- Spiraea Opulifolia L.
- Spiraea Prunifolia Siebold & Zucc. var. plena C.K. Schneid.
- Spiraea Sargentiana Rehder
- Spiraea Sorbifolia L.
- Spiraea Subvillosa Rydb.
- Spiraea Tomentosa L. var. rosea (Raf.) Fernald
- Spiraea Tomentosa L. var. tomentosa
- Spiraea Tomentulosa Rydb.
- Spiraea Trichocarpa Nakai
- Spiraea Ulmaria L.
- Spiraea Virginiana Britton var. serrulata Rehder
- Spiraea Wilsonii Duthie
- Spiraeanthus Cordifolia Kunth [excluded]
- Spiraeanthus Maxim.
- Spiral Ditchgrass - Ruppia Cirrhosa (Petagna) Grande
- Spiral Dog's-tongue - Pseudelephantopus Spirilis (Less.) Cronquist
- Spiral Flag - Costus Villosissimus Jacq.
- Spiral Ginger - Costus Pulverulentus C. Presl
- Spiral Ginger - Costus Scaber Ruiz & Pav.
- Spiral Oxystegus Moss - Oxystegus Spiralis (Grout) H.A. Crum & L.E. Anderson
- Spiral Pondweed - Potamogeton Spirillus Tuck.
- Spiral Sorrel - Oxalis Spiralis G. Don
- Spiralgrass - Tuctoria J. Reeder
- Spiranthes Adnata (Sw.) Benth. ex Fawc.
- Spiranthes Amabilis Ames
- Spiranthes Beckii Lindl.
- Spiranthes Bicolor (Ker Gawl.) Lindl. [excluded]
- Spiranthes Brevilabris Lindl. var. brevilabris
- Spiranthes Brevilabris Lindl. var. floridana (Wherry) Luer
- Spiranthes Cernua (L.) Rich. var. incurva Jennings
- Spiranthes Cernua (L.) Rich. var. ochroleuca (Rydb.) Ames
- Spiranthes Cernua (L.) Rich. var. odorata (Nutt.) Correll
- Spiranthes Cinnabarina (Llave & Lex.) Hemsl.
- Spiranthes Confusa (Garay) Kartesz & Gandhi
- Spiranthes Costaricensis Rchb. f.
- Spiranthes Cranichoides (Griseb.) Cogn.
- Spiranthes Durangensis Ames & C. Schweinf.
- Spiranthes Elata (Sw.) Rich.
- Spiranthes Fawcettii Cogn.
- Spiranthes Gracilis (Bigelow) Beck
- Spiranthes Gracilis (Bigelow) Beck var. brevilabris (Lindl.) Correll
- Spiranthes Gracilis (Bigelow) Beck var. floridana (Wherry) Correll
- Spiranthes Grayi Ames
- Spiranthes Lanceolata (Aubl.) Léon
- Spiranthes Lanceolata (Aubl.) Léon var. luteoalba (Rchb. f.) Luer
- Spiranthes Lanceolata (Aubl.) Léon var. paludicola Luer
- Spiranthes Lineata Lindl.
- Spiranthes Lucayana (Britton) Cogn.
- Spiranthes Michuacana (Llave & Lex.) Hemsl.
- Spiranthes Orchioides (Sw.) A. Rich.
- Spiranthes Parasitica auct. non A. Rich. & Galeotti
- Spiranthes Polyantha auct. non Rchb. f.
- Spiranthes Romanzoffiana Cham. var. diluvialis (Sheviak) S.L. Welsh
- Spiranthes Romanzoffiana Cham. var. porrifolia (Lindl.) Ames & Correll
- Spiranthes Rubrocallosa B.L. Rob. & Greenm.
- Spiranthes Speciosa (Jacq.) A. Rich.
- Spiranthes Stricta Rydb.
- Spiranthes Tortilis (Sw.) Rich.
- Spiranthes Tuberosa Raf. var. grayi (Ames) Fernald
- Spiranthes Unalascensis Spreng.
- Spiranthes ×intermedia auct. non Ames
- Spiranthes ×steigeri Correll
- Spirea - Spiraea L.
- Spirea - Spiraea ×billiardii Hérincq (pro sp.)
- Spirea - Spiraea ×hitchcockii Hess & Stoynoff
- Spirea - Spiraea ×pyramidata Greene (pro sp.)
- Spirea - Spiraea ×subcanescens Rydb. (pro sp.)
- Spirea - Spiraea ×vanhouttei (Briot) Carrière
- Spiritweed - Aegiphila Jacq.
- Spiritweed - Eryngium Foetidum L.
- Spirodela Oligorrhiza (Kurz) Hegelm.
- Spirodela Polyrhiza (L.) Schleiden, orth. var.
- Spirodela Polyrrhiza (L.) Schleid. var. masonii Daubs
- Spirodela Punctata (G. Mey.) C.H. Thomp.
- Spironema Fragrans Lindl.
- Spironema Robbinsii Sanvalle
- Spitsberg Ionaspis Lichen - Ionaspis Spitsbergensis H. Magn.
- Spitsberg Orange Lichen - Caloplaca Spitsbergensis H. Magn.
- Spitzbergen's Buttercup - Ranunculus ×spitzbergensis (Nathorst) Hadac.
- Splachnobryum Bernoullii Müll. Hal.
- Splachnobryum Kieneri R.S. Williams
- Splachnobryum Moss - Splachnobryum Müll. Hal.
- Splachnobryum Moss - Splachnobryum Obtusum (Brid.) Müll. Hal.
- Splachnoid Dung Moss - Tayloria Splachnoides (Schleich. ex Schwägr.) Hook.
- Splachnum Dung Moss - Splachnum Hedw.
- Splachnum Dung Moss - Splachnum Vasculosum Hedw.
- Splachnum Dung Moss - Splachnum Vasculosum Hedw. var. vasculosum
- Splachnum Heterophyllum Drumm.
- Splachnum Melanocaulon (Wahlenb.) Schwägr.
- Splachnum Ovatum Dicks. ex Hedw.
- Splashzone Moss - Scouleria Hook.
- Spleen Amaranth - Amaranthus Dubius Mart. ex Thell.
- Spleenwort - Asplenium L.
- Spleenwort - Asplenium ×alternifolium Wulfen (pro sp.)
- Spleenwort - Asplenium ×biscaynianum (D.C. Eaton) A.A. Eaton (pro sp.)
- Spleenwort - Asplenium ×boydstoniae (Walter) Short
- Spleenwort - Asplenium ×clermontiae Syme
- Spleenwort - Asplenium ×curtissii Underw. (pro sp.)
- Spleenwort - Asplenium ×ebenoides R.R. Scott (pro sp.)
- Spleenwort - Asplenium ×flagrum W.H. Wagner & D.D. Palmer
- Spleenwort - Asplenium ×gravesii Maxon (pro sp.)
- Spleenwort - Asplenium ×herb-wagneri W.C. Taylor & Mohlenbr.
- Spleenwort - Asplenium ×heteroresiliens W.H. Wagner (pro sp.)
- Spleenwort - Asplenium ×inexpectatum (E.L. Braun ex Friesner) Morton
- Spleenwort - Asplenium ×kentuckiense T.N. McCoy (pro sp.)
- Spleenwort - Asplenium ×kokeense W.H. Wagner
- Spleenwort - Asplenium ×morganii W.H. Wagner
- Spleenwort - Asplenium ×shawneense (R.C. Moran) H.E. Ballard
- Spleenwort - Asplenium ×sphenocookii W.H. Wagner
- Spleenwort - Asplenium ×trudellii Wherry (pro sp.)
- Spleenwort - Asplenium ×virginicum Maxon
- Spleenwort - Asplenium ×waikomoi W.H. Wagner & D.D. Palmer
- Spleenwort - Asplenium ×wherryi D.M. Sm.
- Spleenwort Cyanea - Cyanea Aspleniifolia (H. Mann) Hillebr.
- Spleenwort Dwarf Polypody - Grammitis Aspleniifolia (L.) Proctor
- Spleenwort Maiden Fern - Thelypteris Retroflexa (L.) Proctor & Lourteig
- Splendid Bristlegrass - Setaria Sphacelata (Schumach.) Stapf & C.E. Hubb. ex M.B. Moss var. splendida (Stap
- Splendid Feather Moss - Hylocomium Splendens (Hedw.) Schimp.
- Splendid Mariposa Lily - Calochortus Splendens Douglas ex Benth.
- Splendid Woodland-gilia - Saltugilia Splendens (Douglas ex H. Mason & A.D. Grant) L.A. Johnson
- Splendid Woodland-gilia - Saltugilia Splendens (Douglas ex H. Mason & A.D. Grant) L.A. Johnson ssp. splendens
- Splitawn Sedge - Carex Tumulicola Mack.
- Splitbeard Bluestem - Andropogon Ternarius Michx.
- Splitbeard Bluestem - Andropogon Ternarius Michx. var. cabanisii (Hack.) Fernald & Grisc.
- Splitbeard Bluestem - Andropogon Ternarius Michx. var. ternarius
- Splithair Indian Paintbrush - Castilleja Schizotricha Greenm.
- Splitleaf Brickellbush - Brickellia Laciniata A. Gray
- Splitleaf Cyanea - Cyanea Cylindrocalyx (Rock) Lammers
- Splitleaf Cyanea - Cyanea Grimesiana Gaudich.
- Splitleaf Cyanea - Cyanea Grimesiana Gaudich. ssp. grimesiana
- Splitleaf Cyanea - Cyanea Grimesiana Gaudich. ssp. obatae (H. St. John) Lammers
- Splitleaf Gilia - Giliastrum Incisum (Benth.) J.M. Porter
- Splitleaf Groundsel - Packera Dimorphophylla (Greene) W.A. Weber & Á. Löve
- Splitleaf Groundsel - Packera Dimorphophylla (Greene) W.A. Weber & Á. Löve var. dimorphophylla
- Splitleaf Groundsel - Packera Dimorphophylla (Greene) W.A. Weber & Á. Löve var. intermedia (T.M. Barkley) D.K
- Splitleaf Indian Paintbrush - Castilleja Rhexiifolia Rydb.
- Splitlip Hempnettle - Galeopsis Bifida Boenn.
- Spodiopogon Aureus Hook. & Arn.
- Spodiopogon Trin.
- Spokane False Goldenaster - Heterotheca Barbata (Rydb.) Semple
- Spondias Cytherea Sonnerat
- Spondias Lutea L.
- Spondias Pinnata (L. f.) Kurz
- Sponge Gourd - Luffa Aegyptiaca Mill.
- Spongeplant - Limnobium Rich.
- Spontaneous Barley - Hordeum Spontaneum K. Koch
- Spoon Pondweed - Potamogeton ×spathuliformis (J.W. Robbins) Morong (pro sp.)
- Spoon Primrose-willow - Ludwigia Spathulata Torr. & A. Gray
- Spoonleaf - Bouchea Spathulata Torr.
- Spoonleaf Buckwheat - Eriogonum Spathulatum A. Gray
- Spoonleaf Cyanea - Cyanea Kahiliensis (H. St. John) Lammers
- Spoonleaf Cyanea - Cyanea Spathulata (Hillebr.) A. Heller
- Spoonleaf Cyrtandra - Cyrtandra Spathulata H. St. John
- Spoonleaf Peperomia - Peperomia Magnoliifolia (Jacq.) A. Dietr.
- Spoonleaf Purple Everlasting - Gamochaeta Purpurea (L.) Cabrera
- Spoonleaf Rockcress - Arabis Fendleri (S. Watson) Greene var. spatifolia (Rydb.) Rollins
- Spoonleaf Sundew - Drosera Intermedia Hayne
- Spoonleaf Sundew - Drosera Spatulata Labill.
- Spoonleaf Treebine - Cissus Obovata Vahl
- Spoonleaf Yellow Loosestrife - Lysimachia Mauritiana Lam.
- Spoonsepal Spineflower - Chorizanthe Obovata Goodman
- Spoonshape Barbara's Buttons - Marshallia Obovata (Walter) Beadle & F.E. Boynt.
- Spoonshape Barbara's Buttons - Marshallia Obovata (Walter) Beadle & F.E. Boynt. var. obovata
- Spoonshape Barbara's Buttons - Marshallia Obovata (Walter) Beadle & F.E. Boynt. var. scaposa Channell
- Spoonwort - Cochlearia Officinalis L. [excluded]
- Sporastatia Cinerea (Schaerer) Körb.
- Sporastatia Lichen - Sporastatia A. Massal.
- Sporastatia Lichen - Sporastatia Polyspora (Nyl.) Grummann
- Sporastatia Lichen - Sporastatia Testudinea (Ach.) A. Massal.
- Sporobolus Africanus (Poir.) Robyns & Tournay
- Sporobolus Airoides (Torr.) Torr. var. wrightii (Munro ex Scribn.) Gould
- Sporobolus Alopecuroides (Piller & Mitterp.) P.M. Peterson
- Sporobolus Alterniflorus (Loisel.) P.M. Peterson & Saarela
- Sporobolus Anglicus (C.E. Hubbard) P.M. Peterson & Saarela
- Sporobolus Angustus Buckley
- Sporobolus Arcuatus (K.E. Rogers) P.M. Peterson
- Sporobolus Arenicola P.M. Peterson
- Sporobolus Argutus (Nees) Kunth
- Sporobolus Asper (P. Beauv.) Kunth
- Sporobolus Asper (P. Beauv.) Kunth var. canovirens (Nash) Shinners
- Sporobolus Asper (P. Beauv.) Kunth var. clandestinus (Biehler) Shinners
- Sporobolus Asper (P. Beauv.) Kunth var. drummondii (Trin.) Vasey
- Sporobolus Asper (P. Beauv.) Kunth var. hookeri (Trin.) Vasey
- Sporobolus Asper (P. Beauv.) Kunth var. macer (Trin.) Shinners
- Sporobolus Asper (P. Beauv.) Kunth var. pilosus (Vasey) Hitchc.
- Sporobolus Asperifolius (Nees & Meyen ex Trin.) Nees
- Sporobolus Attenuatus Nash
- Sporobolus Australasicus Domin
- Sporobolus Berterianus (Trin.) Hitchc. & Chase
- Sporobolus Brevipilis (Torr.) P.M. Peterson
- Sporobolus Canovirens Nash
- Sporobolus Clandestinus (Biehler) Hitchc. var. canovirens (Nash) Steyerm. & Kucera
- Sporobolus Compositus (Poir.) Merr. var. clandestinus (Biehler) Wipff & S.D. Jones
- Sporobolus Confusus auct. non (Fourn.) Vasey
- Sporobolus Coromandelianus auct. non (Retz.) Kunth
- Sporobolus Cryptandrus (Torr.) A. Gray ssp. fuscicola (Hook.) E.K. Jones & Fassett
- Sporobolus Cryptandrus (Torr.) A. Gray var. fuscicola (Hook.) Pohl
- Sporobolus Cryptandrus (Torr.) A. Gray var. occidentalis E.K. Jones & Fassett
- Sporobolus Cryptandrus (Torr.) A. Gray var. strictus Scribn.
- Sporobolus Cynosuroides (L.) P.M. Peterson & Saarela
- Sporobolus Densiflorus (Brongn.) P.M. Peterson & Saarela
- Sporobolus Diander (Retz.) P. Beauv., orth. var.
- Sporobolus Drummondii (Trin.) Vasey
- Sporobolus Farinosus Hosok.
- Sporobolus Fertilis (Steud.) Clayton
- Sporobolus Fimbriatus (Trin.) Nees var. latifolius Stent
- Sporobolus Foliosus (Trin.) P.M. Peterson & Saarela
- Sporobolus Gracilis (Trin.) Merr.
- Sporobolus Helvolus (Trin.) T. Durand & Schinz
- Sporobolus Hookerianus P.M. Peterson & Saarela
- Sporobolus Indicus (L.) R. Br. var. flaccidus (Roem. & Schult.) Veldkamp
- Sporobolus Ioclados (Trin.) Nees var. usitatus (Stent) Chippind.
- Sporobolus Jacquemontii Kunth
- Sporobolus Lampranthus Pilg.
- Sporobolus Longifolius (Torr.) Alph. Wood
- Sporobolus Macer (Trin.) Hitchc.
- Sporobolus Maritimus (M.A. Curtis) P.M. Peterson & Saarela
- Sporobolus Megalospermus (F. Muell. ex Benth.) P.M. Peterson
- Sporobolus Michauxianus (Hitchc.) P.M. Peterson & Saarela
- Sporobolus Microspermum (Lag.) Hitchc., orth. var.
- Sporobolus Muralis (Raddi) Hitchc. & Chase
- Sporobolus Neglectus Nash var. ozarkanus (Fernald) Steyerm. & Kucera
- Sporobolus Nervosus Hochst.
- Sporobolus Niliaca (Fig. & De Not.) P.M. Peterson
- Sporobolus Ozarkanus Fernald
- Sporobolus Patens auct. non Swallen
- Sporobolus Pilosus Vasey
- Sporobolus Poiretii (Roem. & Schult.) Hitchc.
- Sporobolus Pulvinatus Swallen
- Sporobolus Pumilus (Roth) P.M. Peterson & Saarela
- Sporobolus Ramulosus (Kunth) Kunth
- Sporobolus Rigidus (Buckley) P.M. Peterson
- Sporobolus Rigidus (Buckley) P.M. Peterson var. magnus (Scribn. & Merr.) P.M. Peter
- Sporobolus Rigidus (Buckley) P.M. Peterson var. rigidus
- Sporobolus Schoenoides (L.) P.M. Peterson
- Sporobolus Spartinus (Trin.) P.M. Peterson & Saarela
- Sporobolus Tenacissimus auct.
- Sporobolus Torreyanus (Schult.) Nash
- Sporobolus Uniflorus (Muhl.) Scribn. & Merr.
- Sporobolus Vaginiflorus (Torr. ex A. Gray) Alph. Wood var. inaequalis Fernald
- Sporobolus Vaginiflorus (Torr. ex A. Gray) Alph. Wood var. neglectus (Nash) Scribn.
- Sporobolus Vaseyi P.M. Peterson
- Sporobolus ×eatonianus P.M. Peterson & Saarela
- Sporobolus ×townsendii (H. Groves & J. Groves) P.M. Peterson & Saarela
- Sporopodium Lichen - Sporopodium Mont.
- Sporopodium Lichen - Sporopodium Phyllocharis (Mont.) A. Massal.
- Spotflower - Acmella Rich. ex Pers.
- Spotless Balm - Dicerandra Immaculata Lakela
- Spotless Balm - Dicerandra Immaculata Lakela var. savannarum R.B. Huck
- Spotless Watermeal - Wolffia Arrhiza (L.) Horkel ex Wimm.
- Spotted African Cornlily - Ixia Maculata L.
- Spotted Asian Poppy - Roemeria Refracta DC.
- Spotted Bean - Phaseolus Maculatus Scheele
- Spotted Beebalm - Monarda Fruticulosa Epling
- Spotted Beebalm - Monarda Punctata L.
- Spotted Beebalm - Monarda Punctata L. ssp. immaculata Pennell
- Spotted Beebalm - Monarda Punctata L. ssp. punctata
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. arkansana (E.M. McClint. & Epling) Shinner
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. correllii B.L. Turner
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. coryi (E.M. McClint. & Epling) Shinners
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. intermedia (E.M. McClint. & Epling) Waterf
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. lasiodonta A. Gray
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. occidentalis (Epling) Palmer & Steyerm.
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. punctata
- Spotted Beebalm - Monarda Punctata L. ssp. punctata var. villicaulis (Pennell) Palmer & Steyerm.
- Spotted Bellflower - Campanula Punctata Lam.
- Spotted Buckwheat - Eriogonum Maculatum A. Heller
- Spotted Calla Lily - Zantedeschia Albomaculata (Hook.) Baill.
- Spotted Evening Primrose - Oenothera Canescens Torr. & Frém.
- Spotted Felt Lichen - Sticta (schreb.) Ach.
- Spotted Felt Lichen - Sticta Fuliginosa (Hoffm.) Ach.
- Spotted Felt Lichen - Sticta Limbata (Sm.) Ach.
- Spotted Felt Lichen - Sticta Sylvatica (Huds.) Ach.
- Spotted Fritillary - Fritillaria Atropurpurea Nutt.
- Spotted Geranium - Geranium Maculatum L.
- Spotted Goldenthistle - Scolymus Maculatus L.
- Spotted Gum - Eucalyptus Maculata Hook.
- Spotted Hawkweed - Hieracium Maculatum Sm.
- Spotted Henbit - Lamium Maculatum L.
- Spotted Hideseed - Eucrypta Chrysanthemifolia (Benth.) Greene
- Spotted Hideseed - Eucrypta Chrysanthemifolia (Benth.) Greene var. bipinnatifida (Torr.) Constance
- Spotted Hideseed - Eucrypta Chrysanthemifolia (Benth.) Greene var. chrysanthemifolia
- Spotted Joe Pye Weed - Eutrochium Maculatum (L.) E.E. Lamont
- Spotted Joe Pye Weed - Eutrochium Maculatum (L.) E.E. Lamont var. bruneri (A. Gray) E.E. Lamont
- Spotted Joe Pye Weed - Eutrochium Maculatum (L.) E.E. Lamont var. foliosum (Fernald) E.E. Lamont
- Spotted Joe Pye Weed - Eutrochium Maculatum (L.) E.E. Lamont var. maculatum
- Spotted Knapweed - Centaurea Stoebe L.
- Spotted Knapweed - Centaurea Stoebe L. ssp. micranthos (Gugler) Hayek
- Spotted Lady's Slipper - Cypripedium Guttatum Sw.
- Spotted Lady's Slipper - Cypripedium Yatabeanum Makino
- Spotted Ladysthumb - Polygonum Persicaria L.
- Spotted Lupine - Lupinus Maculatus Rydb.
- Spotted Medick - Medicago Arabica (L.) Huds.
- Spotted Mock Orange - Philadelphus Maculatus (C.L. Hitchc.) Hu
- Spotted Peperomia - Peperomia Maculosa (L.) Hook.
- Spotted Phacelia - Phacelia Maculata Alph. Wood
- Spotted Pondweed - Potamogeton Pulcher Tuck.
- Spotted Sandmat - Chamaesyce Maculata (L.) Small
- Spotted Signal Grass - Brachiaria Nigropedata (Munro ex Ficalho & Hiern) Stapf
- Spotted Snapweed - Impatiens Balsamina L.
- Spotted St. Johnswort - Hypericum Maculatum Crantz
- Spotted St. Johnswort - Hypericum Maculatum Crantz ssp. obtusiusculum (Tourlet) Hayek
- Spotted St. Johnswort - Hypericum Punctatum Lam.
- Spotted Stickseed - Hackelia Patens (Nutt.) I.M. Johnst.
- Spotted Stickseed - Hackelia Patens (Nutt.) I.M. Johnst. var. patens
- Spotted Wakerobin - Trillium Maculatum Raf.
- Spotted Water Hemlock - Cicuta Maculata L.
- Spotted Water Hemlock - Cicuta Maculata L. var. angustifolia Hook.
- Spotted Water Hemlock - Cicuta Maculata L. var. bolanderi (S. Watson) G. Mulligan
- Spotted Water Hemlock - Cicuta Maculata L. var. maculata
- Spotted Water Hemlock - Cicuta Maculata L. var. victorinii (Fernald) B. Boivin
- Spottedheart - Stictocardia Tiliifolia (Desr.) Hallier f.
- Sprague's Eggyolk Lichen - Candelariella Spraguei (Tuck.) Zahlbr.
- Spraguea Monosperma (Greene) Rydb.
- Spraguea Umbellata Torr.
- Spraguea Umbellata Torr. var. caudicifera A. Gray
- Sprangletop - Leptochloa P. Beauv.
- Sprawling Dewberry - Rubus Cubitans Blanch.
- Sprawling Hoarypea - Tephrosia Hispidula (Michx.) Pers.
- Sprawling Schiedea - Schiedea Hookeri A. Gray
- Sprawling Signalgrass - Urochloa Reptans (L.) Stapf
- Sprawling Wirevine - Muehlenbeckia Axillaris (Hook. f.) Walp.
- Spreadfruit Goldenbanner - Thermopsis Divaricarpa A. Nelson
- Spreading Airplant - Tillandsia Utriculata L.
- Spreading Alkaliweed - Cressa Truxillensis Kunth
- Spreading Amaranth - Amaranthus Crassipes Schltdl.
- Spreading Amaranth - Amaranthus Crassipes Schltdl. var. crassipes
- Spreading Amaranth - Amaranthus Crassipes Schltdl. var. warnockii Henrickson
- Spreading Asphead - Aspicarpa Longipes A. Gray
- Spreading Beaksedge - Rhynchospora Divergens Chapm. ex M.A. Curtis
- Spreading Bedstraw - Galium Humifusum M. Bieb.
- Spreading Bellflower - Campanula Patula L.
- Spreading Bladderpod - Lesquerella Gracilis (Hook.) S. Watson
- Spreading Bladderpod - Lesquerella Gracilis (Hook.) S. Watson ssp. gracilis
- Spreading Blazing Star - Liatris Patens G.L. Nesom & Kral
- Spreading Blue-eyed Grass - Sisyrinchium Iridifolium Kunth
- Spreading Bluegrass - Poa Pratensis L. ssp. irrigata (Lindm.) H. Lindb.
- Spreading Buckwheat - Eriogonum Effusum Nutt.
- Spreading Buckwheat - Eriogonum Effusum Nutt. var. effusum
- Spreading Buckwheat - Eriogonum Helichrysoides (Gandog.) Rydb.
- Spreading Bulrush - Scirpus Divaricatus Elliott
- Spreading Chervil - Chaerophyllum Procumbens (L.) Crantz
- Spreading Chervil - Chaerophyllum Procumbens (L.) Crantz var. procumbens
- Spreading Chinchweed - Pectis Prostrata Cav.
- Spreading Cleisostoma - Cleisostoma Porrigens (Fukuy.) Garay
- Spreading Cotoneaster - Cotoneaster Divaricatus Rehder & E.H. Wilson
- Spreading Dewberry - Rubus Jacens Blanch.
- Spreading Dogbane - Apocynum Androsaemifolium L.
- Spreading Eryngo - Eryngium Diffusum Torr.
- Spreading False Pennyroyal - Hedeoma Diffusa Greene
- Spreading False Pimpernel - Lindernia Diffusa (L.) Wettst.
- Spreading False Prairie-clover - Marina Diffusa (Moric.) Barneby
- Spreading Fanpetals - Sida Abutifolia Mill.
- Spreading Fissurewort - Halimolobos Diffusa (A. Gray) O.E. Schulz
- Spreading Fleabane - Erigeron Divergens Torr. & A. Gray
- Spreading Gooseberry - Ribes Divaricatum Douglas
- Spreading Gooseberry - Ribes Divaricatum Douglas var. divaricatum
- Spreading Groundsmoke - Gayophytum Diffusum Torr. & A. Gray
- Spreading Groundsmoke - Gayophytum Diffusum Torr. & A. Gray ssp. diffusum
- Spreading Groundsmoke - Gayophytum Diffusum Torr. & A. Gray ssp. parviflorum F.H. Lewis & Szweykowski
- Spreading Hawthorn - Crataegus Disperma Ashe
- Spreading Hedgeparsley - Torilis Arvensis (Huds.) Link
- Spreading Hedgeparsley - Torilis Arvensis (Huds.) Link ssp. arvensis
- Spreading Hedgeparsley - Torilis Arvensis (Huds.) Link ssp. heterophylla (Guss.) A. Thell
- Spreading Leastdaisy - Chaetopappa Effusa (A. Gray) Shinners
- Spreading Liverseed Grass - Urochloa Decumbens (Stapf) R. Webster
- Spreading Minerslettuce - Montia Diffusa (Nutt.) Greene
- Spreading Moonpod - Selinocarpus Diffusus A. Gray
- Spreading Nailwort - Paronychia Depressa (Torr. & A. Gray) Nutt. ex A. Nelson
- Spreading Navarretia - Navarretia Fossalis Moran
- Spreading Nehe - Lipochaeta Venosa Sherff
- Spreading Panicgrass - Paspalidium Distans (Trin.) Hughes
- Spreading Pellitory - Parietaria Judaica L.
- Spreading Phlox - Phlox Diffusa Benth.
- Spreading Phlox - Phlox Diffusa Benth. ssp. diffusa
- Spreading Phlox - Phlox Diffusa Benth. ssp. longistylis Wherry
- Spreading Phlox - Phlox Diffusa Benth. ssp. scleranthifolia (Rydb.) Wherry
- Spreading Phlox - Phlox Diffusa Benth. ssp. subcarinata Wherry
- Spreading Pygmyleaf - Loeflingia Squarrosa Nutt.
- Spreading Pygmyleaf - Loeflingia Squarrosa Nutt. ssp. artemisiarum Barneby & Twisselmann
- Spreading Pygmyleaf - Loeflingia Squarrosa Nutt. ssp. cactorum Barneby & Twisselmann
- Spreading Pygmyleaf - Loeflingia Squarrosa Nutt. ssp. squarrosa
- Spreading Rockcress - Arabis Patens Sull.
- Spreading Rush - Juncus Patens E. Mey.
- Spreading Sandmat - Chamaesyce Humistrata (Engelm. ex A. Gray) Small
- Spreading Sandwort - Arenaria Lanuginosa (Michx.) Rohrb.
- Spreading Sandwort - Arenaria Lanuginosa (Michx.) Rohrb. ssp. lanuginosa
- Spreading Sandwort - Arenaria Lanuginosa (Michx.) Rohrb. ssp. lanuginosa var. lanuginosa
- Spreading Sandwort - Arenaria Lanuginosa (Michx.) Rohrb. ssp. lanuginosa var. longipedunculata Duncan
- Spreading Sandwort - Arenaria Lanuginosa (Michx.) Rohrb. ssp. saxosa (A. Gray) Maguire
- Spreading Schiedea - Schiedea Diffusa A. Gray
- Spreading Sedge - Carex Laxiculmis Schwein.
- Spreading Sedge - Carex Laxiculmis Schwein. var. copulata (L.H. Bailey) Fernald
- Spreading Sedge - Carex Laxiculmis Schwein. var. laxiculmis
- Spreading Snakeherb - Dyschoriste Schiedeana (Nees) Kuntze var. decumbens (A. Gray) Henrickson
- Spreading Snakeroot - Ageratina Riparia (Regel) R.M. King & H. Rob.
- Spreading Sneezeweed - Centipeda Minima (L.) A. Braun & Asch.
- Spreading Spiderflower - Cleome Diffusa Banks ex DC.
- Spreading Spleenwort - Asplenium Patens Kaulf.
- Spreading Sprangletop - Leptochloa Divaricatissima S.T. Blake
- Spreading Stickseed - Hackelia Diffusa (Lehm.) I.M. Johnst.
- Spreading Stickseed - Hackelia Diffusa (Lehm.) I.M. Johnst. var. diffusa
- Spreading Sweetjuice - Glinus Radiatus (Ruiz & Pav.) Rohrb.
- Spreading Thelypodiopsis - Thelypodiopsis Divaricata (Rollins) S.L. Welsh & Reveal
- Spreading Threeawn - Aristida Cognata Trin. & Rupr.
- Spreading Wallflower - Erysimum Repandum L.
- Spreading Wheatgrass - Elymus Scribneri (Vasey) M.E. Jones
- Spreading Windmill Grass - Chloris Divaricata R. Br.
- Spreading Woodfern - Dryopteris Expansa (C. Presl) Fraser-Jenkins & Jermy
- Spreading Yellow False Foxglove - Aureolaria Patula (Chapm.) Pennell
- Spreading Yellowcress - Rorippa Sinuata (Nutt.) Hitchc.
- Spreadingpod Rockcress - Arabis ×divaricarpa A. Nelson (pro sp.)
- Spreadpetal Dendrobium - Dendrobium Patentifiliforme Hosok.
- Spreadwing - Eurytaenia Torr. & A. Gray
- Sprengel's Plaubelia Moss - Plaubelia Sprengelii (Schwägr.) R.H. Zander
- Sprengel's Sedge - Carex Sprengelii Dewey ex Spreng.
- Sprenger's Asparagus Fern - Asparagus Aethiopicus L.
- Spring Avens - Geum Vernum (Raf.) Torr. & A. Gray
- Spring Biatora Lichen - Biatora Vernalis (L.) Fr.
- Spring Blue Eyed Mary - Collinsia Verna Nutt.
- Spring Cinquefoil - Potentilla Neumanniana Rchb.
- Spring Club Lichen - Multiclavula Vernalis (Schwein.) R. Petersen
- Spring Coralroot - Corallorhiza Wisteriana Conrad
- Spring Creek Bladderpod - Lesquerella Perforata Rollins
- Spring Draba - Draba Verna L.
- Spring Forget-me-not - Myosotis Verna Nutt.
- Spring Fumewort - Corydalis Solida (L.) Clairv.
- Spring Gooseberry - Ribes Watsonianum Koehne
- Spring Hill Flax - Linum Macrocarpum C.M. Rogers
- Spring Lady's Tresses - Spiranthes Vernalis Engelm. & A. Gray
- Spring Lessingia - Lessingia Tenuis (A. Gray) Coville
- Spring Madia - Madia Elegans D. Don ex Lindl. ssp. vernalis D.D. Keck
- Spring Milletgrass - Milium Vernale M. Bieb.
- Spring Mountain Aster - Ionactis Caelestis Leary & G.L. Nesom
- Spring Mountain Milkvetch - Astragalus Remotus (M.E. Jones) Barneby
- Spring Phacelia - Phacelia Verna Howell
- Spring Pheasant's Eye - Adonis Vernalis L.
- Spring Pygmycudweed - Evax Verna Raf.
- Spring Pygmycudweed - Evax Verna Raf. var. drummondii (Torr. & A. Gray) Kartesz & Gandhi
- Spring Pygmycudweed - Evax Verna Raf. var. verna
- Spring Snowflake - Leucojum Vernum L.
- Spring Speedwell - Veronica Verna L.
- Spring Spiderlily - Hymenocallis Liriosme (Raf.) Shinners
- Spring Thistle - Cirsium Vernale (Osterh.) Cockerell
- Spring Vetch - Vicia Lathyroides L.
- Spring-gold - Crocidium Hook.
- Spring-vetch - Lathyrus Vernus (L.) Bernh.
- Springbeauty - Claytonia L.
- Springblossom - Jaborosa Integrifolia Lam.
- Springdale Rockdaisy - Perityle Tenella (M.E. Jones) J.F. Macbr.
- Springfield's Beardgrass - Bothriochloa Springfieldii (Gould) Parodi
- Springflowering Goldenrod - Solidago Verna M.A. Curtis ex Torr. & A. Gray
- Springloving Centaury - Centaurium Namatophilum Reveal, C.R. Broome & Beatley
- Springparsley - Cymopterus Raf.
- Springstar - Tristagma Poepp.
- Springstar - Tristagma Uniflorum (Lindl.) Traub
- Springtape - Sagittaria Kurziana Glück
- Springtime Dewberry - Rubus Scambens L.H. Bailey
- Springville Clarkia - Clarkia Springvillensis Vasek
- Sprouting Broccoli - Brassica Oleracea L. var. italica Plenck
- Sprouting Leaf Willow - Salix Stolonifera Coville
- Spruce Muskeg Sedge - Carex Lugens T. Holm
- Spruce - Picea A. Dietr.
- Spruce Pine - Pinus Glabra Walter
- Sprucefir Fleabane - Erigeron Eximius Greene
- Sprucemont Flax - Linum Subteres (Trel.) Winkl.
- Sprucetop Grama - Bouteloua Chondrosioides (Kunth) Benth. ex S. Watson
- Spurge - Euphorbia Gaudichaudii Boiss.
- Spurge - Euphorbia L.
- Spurge - Euphorbia ×gayeri Boros & Soó ex Soó
- Spurgecreeper - Dalechampia Scandens L.
- Spurgelaurel - Daphne Laureola L.
- Spurless Touch-me-not - Impatiens Ecornuta Gerry Moore, Zika & Rushworth
- Spurred Butterfly Pea - Centrosema Virginianum (L.) Benth.
- Spurred Gentian - Halenia Borkh.
- Spurred Snapdragon - Sairocarpus Cornutus (Benth.) D.A. Sutton
- Spurry Buckwheat - Eriogonum Spergulinum A. Gray
- Spurry Buckwheat - Eriogonum Spergulinum A. Gray var. pratense (S. Stokes) J.T. Howell
- Spurry Buckwheat - Eriogonum Spergulinum A. Gray var. spergulinum
- Spurry - Spergula L.
- Squalid Bruised Lichen - Toninia Squalida (Ach.) A. Massal.
- Squamarina Crassa (Huds.) Poelt
- Square Goose Neck Moss - Rhytidiadelphus Squarrosus (Hedw.) Warnst.
- Square Pleurochaete Moss - Pleurochaete Squarrosa (Brid.) Lindb.
- Squarebud Daisy - Tetragonotheca Texana Engelm. & A. Gray ex A. Gray
- Squareflower - Paronychia Erecta (Chapm.) Shinners
- Squareflower - Paronychia Erecta (Chapm.) Shinners var. corymbosa (Small) Chaudhri
- Squareflower - Paronychia Erecta (Chapm.) Shinners var. erecta
- Squareseed Spurge - Euphorbia Exstipulata Engelm.
- Squarestem Butterflybush - Buddleja Saligna Willd.
- Squarestem - Chrysothemis Pulchella (Donn ex Sims) Decne.
- Squarestem - Melanthera Rohr
- Squarestem Spikerush - Eleocharis Quadrangulata (Michx.) Roem. & Schult.
- Squarrose Knapweed - Centaurea Virgata Lam.
- Squarrose Knapweed - Centaurea Virgata Lam. ssp. squarrosa (Willd.) Gugler
- Squarrose Sedge - Carex Squarrosa L.
- Squashberry - Viburnum Edule (Michx.) Raf.
- Squirrel Corn - Dicentra Canadensis (Goldie) Walp.
- Squirrel's Tail - Justicia Betonica L.
- Squirreltail - Elymus Elymoides (Raf.) Swezey
- Squirreltail - Elymus Elymoides (Raf.) Swezey ssp. brevifolius (J.G. Sm.) Barkworth
- Squirreltail - Elymus Elymoides (Raf.) Swezey ssp. californicus (J.G. Sm.) Barkworth
- Squirreltail - Elymus Elymoides (Raf.) Swezey ssp. elymoides
- Squirreltail - Elymus Elymoides (Raf.) Swezey ssp. hordeoides (Suksd.) Barkworth
- Squirreltail Fescue - Vulpia Elliotea (Raf.) Fernald
- Squirting Cucumber - Ecballium A. Rich.
- Squirting Cucumber - Ecballium Elaterium (L.) A. Rich.
- Sri Lanka Privet - Ligustrum Robustum (Roxb.) Blume var. walkeri (Decne.) P.S. Green
- St. Andrew's Cross - Hypericum Hypericoides (L.) Crantz
- St. Andrew's Cross - Hypericum Hypericoides (L.) Crantz ssp. hypericoides
- St. Andrew's Cross - Hypericum Hypericoides (L.) Crantz ssp. multicaule (Michx. ex Willd.) N. Robson
- St. Anthony Dunes Evening Primrose - Oenothera Psammophila (A. Nelson & J.F. Macbr.) W.L. Wagner, Stockhouse & Klein
- St. Anthony's Turnip - Ranunculus Bulbosus L.
- St. Augustine Grass - Stenotaphrum Secundatum (Walter) Kuntze
- St. Augustine Grass - Stenotaphrum Trin.
- St. Catherine's Lace - Eriogonum Giganteum S. Watson
- St. Catherine's Lace - Eriogonum Giganteum S. Watson var. giganteum
- St. Eustatius Threeawn - Aristida Suringarii Henr.
- St. Francis Cabbage - Stanfordia Californica S. Watson
- St. Jacob Texosporium Lichen - Texosporium Santi-jacobi (Tuck.) Nadv.
- St. John's Bread - Ceratonia Siliqua L.
- St. John's Melicope - Melicope Saint-johnii (Hume) T.G. Hartley & B.C. Stone
- St. John's Phyllostegia - Phyllostegia Micrantha H. St. John
- St. John's Rollandia - Cyanea St.-johnii (Hosaka) Lammers, Givnish & Systma
- St. John's Rosemallow - Hibiscus Kokio Hillebr. ex Wawra ssp. saintjohnianus (Roe) D.M. Bates
- St. Johnswort - Hypericum L.
- St. Johnswort - Hypericum Pulchrum L.
- St. Johnswort - Hypericum ×moserianum Luquet ex André
- St. Lawrence Bladderfern - Cystopteris Laurentiana (Weath.) Blasdell
- St. Lawrence Dewberry - Rubus Paganus L.H. Bailey
- St. Lawrence Waterhorehound - Lycopus Laurentianus Rolland-Germain
- St. Mark's False Foxglove - Agalinis Pulchella Pennell
- St. Marks Yelloweyed Grass - Xyris Panacea L.C. Anderson & Kral
- St. Marys Peak Bladderpod - Lesquerella Humilis Rollins
- St. Paul's Wort - Sigesbeckia L.
- St. Peterswort - Hypericum Crux-andreae (L.) Crantz
- St. Thomas Bean - Entada Phaseoloides (L.) Merr.
- St. Thomas Lidpod - Operculina Turpethum (L.) Silva Manso
- St. Thomas Lidpod - Operculina Turpethum (L.) Silva Manso var. turpethum
- St. Thomas Lidpod - Operculina Turpethum (L.) Silva Manso var. ventricosa (Bertero) Austin & Staples
- St. Thomas Pricklyash - Zanthoxylum Thomasianum (Krug & Urb.) Krug & Urb. ex P. Wilson
- St. Thomas Staggerbush - Lyonia Rubiginosa (Pers.) G. Don
- St. Thomas Staggerbush - Lyonia Rubiginosa (Pers.) G. Don var. rubiginosa
- St. Thomas Tree - Bauhinia Tomentosa L.
- Stachydeoma Angulata Tharp
- Stachys Agraria auct. non Cham. & Schltdl.
- Stachys Ajugoides Benth. var. ajugoides
- Stachys Ajugoides Benth. var. rigida Jeps. & Hoover
- Stachys Ambigua (A. Gray) Britton
- Stachys Arenicola Britton
- Stachys Asperrima Rydb.
- Stachys Atlantica Britton
- Stachys Borealis Rydb.
- Stachys Ciliata Douglas ex Benth.
- Stachys Ciliata Epling
- Stachys Cooleyae A. Heller
- Stachys Cretica L. [excluded]
- Stachys Emersonii Piper
- Stachys Germanica L. var. italica (Mill.) Briq.
- Stachys Glabra Riddell
- Stachys Grandiflora (Stephan ex Willd.) Benth., nom. illeg.
- Stachys Grayana House
- Stachys Hirta L.
- Stachys Hispida Pursh
- Stachys Homotricha (Fernald) Rydb.
- Stachys Hyssopifolia Michx. var. ambigua A. Gray
- Stachys Hyssopifolia Michx. var. lythroides (Small) J.B. Nelson
- Stachys Italica Mill.
- Stachys Lythroides Small
- Stachys Nuttallii Shuttlw. ex Benth.
- Stachys Olympica Poir.
- Stachys Palustris L. ssp. arenicola (Britton) Gill
- Stachys Palustris L. ssp. pilosa (Nutt.) Epling
- Stachys Palustris L. var. elliptica Clos
- Stachys Palustris L. var. hispida (Pursh) B. Boivin
- Stachys Palustris L. var. homotricha Fernald
- Stachys Palustris L. var. macrocalyx Jennings
- Stachys Palustris L. var. nipigonensis Jennings
- Stachys Palustris L. var. petiolata Clos
- Stachys Palustris L. var. phaneropoda Weath.
- Stachys Palustris L. var. pilosa (Nutt.) Fernald
- Stachys Palustris L. var. puberula Jennings
- Stachys Palustris L. var. segetum (Mutel) Grogn.
- Stachys Riddellii House
- Stachys Rigida Nutt. ex Benth. ssp. lanata Epling
- Stachys Rigida Nutt. ex Benth. ssp. quercetorum (A. Heller) Epling
- Stachys Rigida Nutt. ex Benth. ssp. rivularis (A. Heller) Epling
- Stachys Salvioides Small
- Stachys Scopulorum Greene
- Stachys Sieboldii Miq.
- Stachys Subcordata Rydb.
- Stachys Tenuifolia Willd. var. aspera (Michx.) Fernald
- Stachys Tenuifolia Willd. var. hispida (Pursh) Fernald
- Stachys Tenuifolia Willd. var. latidens (Small ex Britton) J.B. Nelson
- Stachys Tenuifolia Willd. var. perlonga Fernald
- Stachys Tenuifolia Willd. var. platyphylla Fernald
- Stachys Teucriifolia Rydb.
- Stachys Teucriiformis Rydb.
- Stachys Tuberifera Naudin
- Stachytarpheta Dichotoma (Ruiz & Pav.) Vahl
- Stachytarpheta Dichotoma auct. non (Ruiz & Pav.) Vahl
- Stachytarpheta Indica Vahl
- Stachytarpheta Speciosa Pohl ex Schauer [excluded]
- Stackhousia Intermedia F.M. Bailey
- Stackhousia Sm.
- Staggerbush - Lyonia Nutt.
- Staggers Grass - Melica Decumbens Thunb.
- Staggerweed - Stachys Arvensis (L.) L.
- Staghorn Cholla - Cylindropuntia Versicolor (Engelm. ex J.M. Coult.) F.M. Knuth
- Staghorn Cinquefoil - Potentilla Bimundorum Soják
- Staghorn Clubmoss - Lycopodiella Cernua (L.) Pic. Serm.
- Staghorn Clubmoss - Lycopodiella Cernua (L.) Pic. Serm. var. cernua
- Staghorn Clubmoss - Lycopodiella Cernua (L.) Pic. Serm. var. curvata (Sw.) Kartesz & Gandhi
- Staghorn Fern - Platycerium Desv.
- Staghorn Fern - Platycerium Superbum de Jonch. & Hennipman
- Staghorn Sumac - Rhus Typhina L.
- Stahl's Staggerbush - Lyonia Rubiginosa (Pers.) G. Don var. stahlii (Urb.) W.S. Judd
- Stahl's Stopper - Eugenia Stahlii (Kiaersk.) Krug & Urb.
- Stahl's Valamuerto - Senna Pendula (Humb. & Bonpl. ex Willd.) Irwin & Barneby var. stahlii (Urb.) I
- Stahlia - Stahlia Bello
- Staining Collomia - Collomia Tinctoria Kellogg
- Stalked Bulrush - Scirpus Pedicellatus Fernald
- Stalked Bur Grass - Tragus Racemosus (L.) All.
- Stalked Fleabane - Erigeron Algidus Jeps.
- Stalked Maidenhair - Adiantum Petiolatum Desv.
- Stalked Moonwort - Botrychium Pedunculosum W.H. Wagner
- Stalked Popcornflower - Plagiobothrys Stipitatus (Greene) I.M. Johnst.
- Stalked Popcornflower - Plagiobothrys Stipitatus (Greene) I.M. Johnst. var. micranthus (Piper) I.M. Johnst.
- Stalked Popcornflower - Plagiobothrys Stipitatus (Greene) I.M. Johnst. var. stipitatus
- Stalked Saltbush - Atriplex Argentea Nutt. ssp. argentea var. caput-medusae (Eastw.) Fosberg
- Stalked Spikemoss - Selaginella Substipitata Spring
- Stalked Wild Petunia - Ruellia Pedunculata Torr. ex A. Gray
- Stalked Wild Petunia - Ruellia Pedunculata Torr. ex A. Gray ssp. pedunculata
- Stalked Wild Petunia - Ruellia Pedunculata Torr. ex A. Gray ssp. pinetorum (Fernald) R.W. Long
- Stalked-flower Johnnyberry - Miconia Theaezans (Bonpl.) Cogn.
- Stalkflower - Nesaea Longipes A. Gray
- Stalkgrain Sedge - Carex Stipata Muhl. ex Willd. var. maxima Chapm.
- Stalkgrass - Pharus L.
- Stalkleaf Murainagrass - Ischaemum Timorense Kunth
- Stalkless Yellowcress - Rorippa Sessiliflora (Nutt.) Hitchc.
- Stalkpod Locoweed - Oxytropis Podocarpa A. Gray
- Standing Milkvetch - Astragalus Laxmannii Jacq. var. tananaicus (Hultén) Barneby & S.L. Welsh
- Standing-cypress - Ipomopsis Rubra (L.) Wherry
- Standish's Honeysuckle - Lonicera Standishii Jacques
- Standley's Bloodleaf - Iresine Heterophylla Standl.
- Standley's Draba - Draba Standleyi J.F. Macbr. & Payson
- Standley's Goosefoot - Chenopodium Standleyanum Aellen
- Standley's Spikemoss - Selaginella Densa Rydb. var. standleyi (Maxon) R. Tryon
- Stanfield's Beebalm - Monarda Stanfieldii Small
- Stanford Orange Lichen - Caloplaca Stanfordensis H. Magn.
- Stanford Tortula Moss - Tortula Stanfordensis Steere
- Stanford's Manzanita - Arctostaphylos Stanfordiana Parry
- Stanford's Manzanita - Arctostaphylos Stanfordiana Parry ssp. stanfordiana
- Stanford's Wart Lichen - Verrucaria Stanfordii Herre
- Stanfordia - Stanfordia S. Watson
- Stanhopea - Stanhopea J. Frost ex Hook.
- Stanley Creek Draba - Draba Trichocarpa Rollins
- Stanleya Annua M.E. Jones
- Stanleya Bipinnata Greene
- Stanleya Integrifolia James ex Torr.
- Stanleya Pinnata (Pursh) Britton ssp. inyoensis Munz & Roos
- Stanleya Pinnata (Pursh) Britton var. gibberosa Rollins
- Stanleya Pinnata (Pursh) Britton var. typica Rollins
- Stanleya Rara A. Nelson
- Stanleya Viridiflora Nutt. var. confertiflora B.L. Rob.
- Stanleya Washitana Muhl. ex DC., nom. utique rej.
- Stanleyella Wrightii (A. Gray) Rydb.
- Stanleyella Wrightii (A. Gray) Rydb. var. tenella (M.E. Jones) Payson
- Stansbury Cliffrose - Purshia Stansburiana (Torr.) Henrickson
- Stansbury's Rockdaisy - Perityle Stansburyi (A. Gray) J.F. Macbr.
- Stansell's Fleabane - Erigeron Stanselliae K.L. Chambers
- Stapelia Nobilis N.E. Br.
- Stapelia - Stapelia L.
- Stapelia Variegata L.
- Stapfia Colusana Burtt Davy
- Star Apple - Chrysophyllum Cainito L.
- Star Campylium Moss - Campylium Stellatum (Hedw.) C.E.O. Jensen
- Star Campylium Moss - Campylium Stellatum (Hedw.) C.E.O. Jensen var. protensum (Brid.) Bryhn
- Star Campylium Moss - Campylium Stellatum (Hedw.) C.E.O. Jensen var. stellatum
- Star Chickweed - Stellaria Pubera Michx.
- Star Cloak Fern - Notholaena Standleyi Maxon
- Star Clover - Trifolium Stellatum L.
- Star Coccocarpia Lichen - Coccocarpia Stellata Tuck.
- Star Duckweed - Lemna Trisulca L.
- Star Gentian - Gentiana Cruciata L.
- Star Gilia - Gilia Stellata A. Heller
- Star Jasmine - Jasminum Multiflorum (Burm. f.) Andrews
- Star Magnolia - Magnolia Stellata (Siebold & Zucc.) Maxim.
- Star Milkvine - Matelea Biflora (Raf.) Woodson
- Star Of Bethlehem - Gagea Fistulosa (Ramond ex DC.) Ker Gawl., nom. illeg.
- Star Of Bethlehem - Ornithogalum L.
- Star Of Bethlehem - Ornithogalum Umbellatum L.
- Star Orchid - Epidendrum L.
- Star Orchid - Epidendrum ×obrienianum Rolfe
- Star Peak Fleabane - Erigeron Salishii G.W. Douglas & Packer
- Star Phacelia - Phacelia Stellaris Brand
- Star Reindeer Lichen - Cladina Stellaris (Opiz) Brodo
- Star Reindeer Lichen - Cladina Stellaris (Opiz) Brodo var. aberrans (Abbayes) Ahti
- Star Sedge - Carex Echinata Murray
- Star Sedge - Carex Echinata Murray ssp. echinata
- Star Sedge - Carex Echinata Murray ssp. phyllomanica (W. Boott) Reznicek
- Star Tickseed - Coreopsis Pubescens Elliott
- Star Tickseed - Coreopsis Pubescens Elliott var. debilis (Sherff) E.B. Sm.
- Star Tickseed - Coreopsis Pubescens Elliott var. pubescens
- Star Tickseed - Coreopsis Pubescens Elliott var. robusta A. Gray ex Eames
- Star-grass - Hypoxis Kilimanjarica Baker
- Star-grass - Hypoxis L.
- Star-mustard - Coincya Monensis (L.) Greuter & Burdet
- Star-mustard - Coincya Monensis (L.) Greuter & Burdet ssp. recurvata (All.) Leadley
- Star-mustard - Coincya Rouy
- Staranise Tree - Illicium Verum Hook. f.
- Starbur - Acanthospermum Schrank
- Starch Grape Hyacinth - Muscari Neglectum Guss. ex Ten.
- Starfern - Hemionitis Palmata L.
- Starflower Brodiaea - Brodiaea Stellaris S. Watson
- Starflower Pincushions - Scabiosa Stellata L.
- Starflower - Trientalis Borealis Raf.
- Starflower - Trientalis Borealis Raf. ssp. borealis
- Starflower - Trientalis L.
- Stargrass - Cynodon Plectostachyus (K. Schum.) Pilg.
- Starhair Groundcherry - Physalis Viscosa L.
- Starhorn - Hygrophila Corymbosa (Blume) Lindau
- Starke's Brachythecium Moss - Brachythecium Starkei (Brid.) Schimp.
- Starke's Kiaeria Moss - Kiaeria Starkei (F. Weber & D. Mohr) I. Hagen
- Starke's Pottia Moss - Pottia Starkeana (Hedw.) Müll. Hal.
- Starkea Pinnata Nutt.
- Starleaf Begonia - Begonia Heracleifolia Cham. & Schltdl.
- Starlet Spineflower - Chorizanthe Stellulata Benth.
- Starlily - Leucocrinum Nutt. ex A. Gray
- Starrush Whitetop - Rhynchospora Colorata (L.) H. Pfeiffer
- Starry Bedstraw - Galium Stellatum Kellogg
- Starry Bedstraw - Galium Stellatum Kellogg ssp. eremicum (Hilend & J.T. Howell) Ehrend.
- Starry False Lily Of The Valley - Maianthemum Stellatum (L.) Link
- Starry Rosette Lichen - Physcia Stellaris (L.) Nyl.
- Starry Rosinweed - Silphium Asteriscus L.
- Starry Rosinweed - Silphium Asteriscus L. var. angustatum A. Gray
- Starry Rosinweed - Silphium Asteriscus L. var. asteriscus
- Starry Rosinweed - Silphium Asteriscus L. var. laevicaule DC.
- Starry Spikemoss - Selaginella Stellata Spring
- Starscale Fern - Pleopeltis Astrolepis (Liebm.) Fourn.
- Starved Fleabane - Erigeron Miser A. Gray
- Starved Panicgrass - Dichanthelium Depauperatum (Muhl.) Gould
- Starveling Milkvetch - Astragalus Jejunus S. Watson
- Starveling Milkvetch - Astragalus Jejunus S. Watson var. articulatus Dorn
- Starveling Milkvetch - Astragalus Jejunus S. Watson var. jejunus
- Starvine - Brandegea Cogn.
- Starviolet - Hedyotis L.
- Starwort - Stellaria L.
- Stately Maiden Fern - Thelypteris Grandis A.R. Sm.
- Stately Rose Gentian - Sabatia Formosa Buckley
- Statice Interior Raup
- Statice Limonium L.
- Statice - Limonium Leptostachyum (Boiss.) Kuntz
- Statice Perezii Stapf
- Statice Sinuata L.
- Statice Welwitschii (Boiss.) Samp.
- Staurothele Ambrosiana (A. Massal.) Zschacke
- Staurothele Areolata (Ach.) Lettau
- Staurothele Circinata Tuck.
- Staurothele Clopima (Wahlenb.) Th. Fr.
- Staurothele Clopima sensu Th. Fr.
- Staurothele Effigurata J.W. Thomson
- Staurothele Elenkinii Oksner
- Staurothele Fuscocuprea (Nyl.) Zschacke
- Staurothele Glacialis Herre
- Staurothele Hazslinskyi (Körb.) Blomb. & Forss.
- Staurothele Hymenogonia (Nyl.) Th. Fr.
- Staurothele Monicae (Zahlbr.) Wetmore
- Staurothele Orispruinosa J.W. Thomson
- Staurothele Perradiata Lynge
- Staurothele Polygonia de Lesd.
- Staurothele Rufa (A. Massal.) Zschacke
- Staurothele Rugosa J.W. Thomson
- Staurothele Sessilis H. Magn.
- Staurothele Succedens (Rehm) Arnold
- Staurothele Umbrina (Wahlenb.) Tuck.
- Staurothele Verruculosa J.W. Thomson
- Stebbin's Bluegrass - Poa Stebbinsii Soreng
- Stebbins' Barley - ×elyhordeum Stebbinsianum (Bowden) Bowden
- Stebbins' Desertdandelion - Malacothrix Stebbinsii W.S. Davis & P.H. Raven
- Stebbins' Desertparsley - Lomatium Stebbinsii Schlessman & Constance
- Stebbins' False Bindweed - Calystegia Stebbinsii Brummitt
- Stebbins' Hedgenettle - Stachys Stebbinsii G. Mulligan & D. Munro
- Stebbins' Lewisia - Lewisia Stebbinsii Gankin & Hildreth
- Stebbins' Phacelia - Phacelia Stebbinsii Constance & Heckard
- Stebbins' Tarweed - Harmonia Stebbinsii (T.W. Nelson & J.P. Nelson) B.G. Baldw.
- Stebbinsoseris Decipiens (K.L. Chambers) Chambers, nom. illeg.
- Stebbinsoseris Heterocarpa (Nutt.) K.L. Chambers, nom. illeg.
- Steele's Dewberry - Rubus Steelei L.H. Bailey
- Steele's Eupatorium - Eutrochium Steelei (E.E. Lamont) E.E. Lamont
- Steen Mountain Thistle - Cirsium Peckii L.F. Hend.
- Steens Indian Paintbrush - Castilleja Pilosa (S. Watson) Rydb. var. steenensis (Pennell) N.H. Holmgren
- Steens Mountain Cushion Buckwheat - Eriogonum Ovalifolium (Gand.) Reveal & Mansfield var. rubidum
- Steeplebush - Spiraea Tomentosa L.
- Steere's Pylaisiella Moss - Pylaisiella Steerei Ando & Higuchi
- Steere's Sphagnum - Sphagnum Steerei R.E. Andrus
- Steerecleus Moss - Steerecleus H. Rob.
- Steerecleus Moss - Steerecleus Serrulatus (Hedw.) H. Rob.
- Stegnosperma - Stegnosperma Benth.
- Stegonia Latifolia (Schwägr.) Vent. ex Broth. var. pilifera (Brid.) Broth.
- Stegonia Moss - Stegonia Pilifera (Brid.) H.A. Crum & L.E. Anderson
- Stegonia Moss - Stegonia Vent.
- Steinchisma Laxum (Sw.) Zuloaga
- Steiner's Lecidea Lichen - Lecidea Steineri Hertel
- Steinia Lichen - Steinia Geophana (Nyl.) Stein
- Steinia Lichen - Steinia Körb.
- Steironema Ciliatum (L.) Baudo
- Steironema Gramineum Greene
- Steironema Heterophyllum (Michx.) Baudo
- Steironema Hybridum (Michx.) Raf. ex B.D. Jacks.
- Steironema Intermedium Kearney
- Steironema Laevigatum Howell
- Steironema Lanceolatum (Walter) A. Gray
- Steironema Lanceolatum (Walter) A. Gray var. hybridum (Michx.) A. Gray
- Steironema Pumilum Greene
- Steironema Quadriflorum (Sims) Hitchc.
- Steironema Radicans (Hook.) A. Gray
- Steironema Tonsum (Alph. Wood) E.P. Bicknell ex Britton
- Stelechocarpus - Stelechocarpus (blume) Hook. f. & Thomson
- Stellar Calcareous Moss - Mnium Stellare Hedw.
- Stellar Hau Kuahiwi - Hibiscadelphus Stellatus H. Oppenh., Bustamente & Perlman
- Stellaria Apetala Ucria ex Roem.
- Stellaria Apetala auct. non Ucria ex Roem.
- Stellaria Aquatica (L.) Scop.
- Stellaria Arenicola Raup
- Stellaria Atrata (J.W. Moore) B. Boivin
- Stellaria Biflora L.
- Stellaria Bongardiana Fernald, nom. inq.
- Stellaria Borealis Bigelow ssp. bongardiana (Fernald) Piper & Beattie
- Stellaria Borealis Bigelow var. bongardiana Fernald
- Stellaria Borealis Bigelow var. borealis
- Stellaria Borealis Bigelow var. crispa (Cham. & Schltdl.) Fenzl ex Torr. & A. Gray
- Stellaria Borealis Bigelow var. floribunda Fernald
- Stellaria Borealis Bigelow var. isophylla Fernald
- Stellaria Borealis Bigelow var. simcoei (Howell) Fernald
- Stellaria Borealis Bigelow var. sitchana (Steud.) Fernald
- Stellaria Brachypetala Bong. var. bongardiana (Fernald) Fernald, nom. inq.
- Stellaria Calycantha (Ledeb.) Bong. ssp. interior Hultén
- Stellaria Calycantha (Ledeb.) Bong. var. bongardiana (Fernald) Fernald
- Stellaria Calycantha (Ledeb.) Bong. var. floribunda (Fernald) Fernald
- Stellaria Calycantha (Ledeb.) Bong. var. isophylla (Fernald) Fernald
- Stellaria Calycantha (Ledeb.) Bong. var. latifolia B. Boivin
- Stellaria Calycantha (Ledeb.) Bong. var. laurentiana Fernald
- Stellaria Calycantha (Ledeb.) Bong. var. simcoei (Howell) Fernald
- Stellaria Calycantha (Ledeb.) Bong. var. sitchana (Steud.) Fernald
- Stellaria Cerastioides L., orth. var.
- Stellaria Cerastoides L.
- Stellaria Dichotoma L. var. americana Porter ex B.L. Rob.
- Stellaria Dulcis Gervais
- Stellaria Edwardsii R. Br.
- Stellaria Edwardsii R. Br. var. arctica (Schischkin) Hultén
- Stellaria Fennica auct. non (Murb.) Perf.
- Stellaria Glauca With.
- Stellaria Gonomischa B. Boivin
- Stellaria Graminea L. var. latifolia Peterm.
- Stellaria Hultenii B. Boivin
- Stellaria Humifusa Rottb. var. oblongifolia Fenzl
- Stellaria Humifusa Rottb. var. suberecta B. Boivin
- Stellaria Jamesiana Torr.
- Stellaria Labradorica Schrenk
- Stellaria Laeta Richardson
- Stellaria Laeta Richardson var. altocaulis (Hultén) B. Boivin
- Stellaria Lagunensis M.E. Jones
- Stellaria Laxmannii Fisch.
- Stellaria Longifolia Muhl. ex Willd. var. laeta (Richardson) S. Watson
- Stellaria Longipes Goldie ssp. monantha (Hultén) W.A. Weber
- Stellaria Longipes Goldie ssp. stricta (Richardson) W.A. Weber
- Stellaria Longipes Goldie var. altocaulis (Hultén) C.L. Hitchc.
- Stellaria Longipes Goldie var. arenicola (Raup) B. Boivin
- Stellaria Longipes Goldie var. edwardsii (R. Br.) A. Gray
- Stellaria Longipes Goldie var. laeta (Richardson) S. Watson
- Stellaria Longipes Goldie var. longipes
- Stellaria Longipes Goldie var. monantha (Hultén) S.L. Welsh
- Stellaria Longipes Goldie var. subvestita (Greene) Polunin
- Stellaria Media (L.) Vill. var. glaberrima G. Beck, sensu Fernald
- Stellaria Media (L.) Vill. var. procera Klett & Richt.
- Stellaria Monantha Hultén
- Stellaria Monantha Hultén ssp. atlantica Hultén
- Stellaria Monantha Hultén var. altocaulis Hultén
- Stellaria Monantha Hultén var. atlantica (Hultén) B. Boivin
- Stellaria Muscorum Fassett
- Stellaria Neglecta Weihe
- Stellaria Nuttallii Torr. & A. Gray
- Stellaria Pallida (Dumort.) Crép.
- Stellaria Palmeri (Rydb.) Tidestr.
- Stellaria Paludicola Fernald & B.G. Schub.
- Stellaria Praecox A. Nelson
- Stellaria Pubera Michx. var. sylvatica (Beguinot) Weath.
- Stellaria Simcoei (Howell) C.L. Hitchc.
- Stellaria Sitchana Steud.
- Stellaria Sitchana Steud. var. bongardiana (Fernald) Hultén
- Stellaria Stricta Richardson
- Stellaria Subvestita Greene
- Stellaria Sylvatica (Beguinot) Maguire
- Stellaria Tennesseensis (C. Mohr) Strausbaugh & Core
- Stellaria Uliginosa Murray
- Stellaria Uniflora Walter
- Stellaria Valida (Goodding) J.M. Coult. & A. Nelson
- Stellaria Viridula (Piper) H. St. John
- Stellaria Washingtoniana B.L. Rob.
- Stellaria Weberi B. Boivin
- Stellariomnium Blyttii (Bruch & Schimp.) M.C. Bowers
- Stellariomnium Stellare (Hedw.) M.C. Bowers
- Stellate Orthotrichum Moss - Orthotrichum Stellatum Brid.
- Stellate Sedge - Carex Albicans Willd. ex Spreng. var. australis (L.H. Bailey) J. Rettig
- Stem Raillardella - Raillardella Scaposa (A. Gray) A. Gray
- Stemless Beardtongue - Penstemon Acaulis L.O. Williams
- Stemless Dwarf Lupine - Lupinus Caespitosus Nutt.
- Stemless Dwarf Lupine - Lupinus Caespitosus Nutt. var. caespitosus
- Stemless Dwarf-cudweed - Hesperevax Acaulis (Kellogg) Greene
- Stemless Dwarf-cudweed - Hesperevax Acaulis (Kellogg) Greene var. acaulis
- Stemless Dwarf-cudweed - Hesperevax Acaulis (Kellogg) Greene var. ambusticola Morefield
- Stemless Dwarf-cudweed - Hesperevax Acaulis (Kellogg) Greene var. robustior Morefield
- Stemless Evening Primrose - Oenothera Triloba Nutt.
- Stemless Four-nerve Daisy - Tetraneuris Acaulis (Pursh) Greene
- Stemless Four-nerve Daisy - Tetraneuris Acaulis (Pursh) Greene var. acaulis
- Stemless Four-nerve Daisy - Tetraneuris Acaulis (Pursh) Greene var. epunctata (A. Nelson) Kartesz & Gandhi
- Stemless Four-nerve Daisy - Tetraneuris Acaulis (Pursh) Greene var. nana (S.L. Welsh) Kartesz & Gandhi
- Stemless Indian Parsley - Aletes Acaulis (Torr.) J.M. Coult. & Rose
- Stemless Ironweed - Vernonia Acaulis (Walter) Gleason
- Stemless Mock Goldenweed - Stenotus Acaulis (Nutt.) Nutt.
- Stemless Spiderwort - Tradescantia Subacaulis Bush
- Stemless Thistle - Onopordum Acaulon L.
- Stemless Townsend Daisy - Townsendia Exscapa (Richardson) Porter
- Stemmermann's' Clubmoss - Huperzia Stemmermanniae (A.C. Medeiros & W.H. Wagner) Kartesz
- Stemmodontia Calycina (Rich.) O.E. Schulz
- Stemmy Four-nerve Daisy - Tetraneuris Scaposa (DC.) Greene
- Stemmy Four-nerve Daisy - Tetraneuris Scaposa (DC.) Greene var. argyrocaulon (K.F. Parker) K.F. Parker
- Stemmy Four-nerve Daisy - Tetraneuris Scaposa (DC.) Greene var. linearis (Nutt.) Parker
- Stemmy Four-nerve Daisy - Tetraneuris Scaposa (DC.) Greene var. scaposa
- Stemodia Arizonica Pennell
- Stemodia Tomentosa (Mill.) Greenm. & C.H. Thomp.
- Stemonurus Blume
- Stemsucker - Pilostyles Guill.
- Stenactis Annua (L.) Nees
- Stenactis Strigosa (Muhl. ex Willd.) DC.
- Stenandrium Fasciculare auct. non (Benth.) Wassh.
- Stenandrium Floridanum (A. Gray) Small
- Stenanthella Occidentalis (A. Gray) Rydb.
- Stenanthium Densum (Desr.) Zomlefer & Judd
- Stenanthium Leimanthoides (A. Gray) Zomlefer & Judd
- Stenanthium Robustum S. Watson
- Stenhammar's Pore Lichen - Pertusaria Stenhammari Hellb.
- Stenocarpus R. Br.
- Stenocarpus Sinuatus (A. Cunn.) Endl. [excluded]
- Stenocereus Hystrix (Haw.) Buxbaum
- Stenocereus Peruvianus auct. non Kiesling, nom. illeg.
- Stenocereus - Stenocereus (a. Berger) Riccob.
- Stenochlaena Amydrophlebia Slosson ex Maxon
- Stenochlaena Kunzeana C. Presl ex Underw.
- Stenochlaena Sorbifolia (L.) J. Sm.
- Stenochlaena - Stenochlaena J. Sm.
- Stenocybe Byssacea (Fr.) Körb.
- Stenocybe Clavata Tibell
- Stenocybe Euspora (Nyl.) Anzi
- Stenocybe Lichen - Stenocybe (nyl.) Körb.
- Stenocybe Lichen - Stenocybe Major (Nyl.) Körb.
- Stenocybe Lichen - Stenocybe Minutissima (G. Merr.) Zahlbr.
- Stenocybe Lichen - Stenocybe Pullatula (Ach.) Stein
- Stenocybe Lichen - Stenocybe Tremulicola Norrlin ex Nyl.
- Stenogyne Affinis Forbes
- Stenogyne Affinis Forbes var. degeneri Sherff
- Stenogyne Affinis Forbes var. retrorsa O. Deg. & Sherff
- Stenogyne Angustifolia A. Gray var. hillebrandii Sherff
- Stenogyne Angustifolia A. Gray var. mauiensis Sherff
- Stenogyne Angustifolia A. Gray var. meeboldii Sherff
- Stenogyne Angustifolia A. Gray var. salicifolia Sherff
- Stenogyne Angustifolia A. Gray var. spathulata Sherff
- Stenogyne Biflora (Sherff) H. St. John
- Stenogyne Calaminthoides A. Gray var. oxydonta Sherff
- Stenogyne Calaminthoides A. Gray var. subrotunda Sherff
- Stenogyne Calaminthoides A. Gray var. waimeana Sherff
- Stenogyne Crenata A. Gray
- Stenogyne Crenata A. Gray var. muricata O. Deg. & Sherff
- Stenogyne Diffusa A. Gray
- Stenogyne Diffusa A. Gray var. glabra Wawra
- Stenogyne Glabrata (Hillebr.) Sherff
- Stenogyne Hirsutula H. St. John
- Stenogyne Kaalae Wawra var. coriacea O. Deg. & Sherff
- Stenogyne Kaalae Wawra var. latisepala Sherff
- Stenogyne Kamehamehae Wawra var. albiflora Sherff
- Stenogyne Kauaulaensis K.R. Wood & H. Oppenh.
- Stenogyne Kealiae Wawra var. angustata O. Deg. & Sherff, nom. inq.
- Stenogyne Macrantha Benth. var. amicarum O. Deg. & Sherff
- Stenogyne Macrantha Benth. var. gracilis Sherff
- Stenogyne Macrantha Benth. var. grayi H. Mann
- Stenogyne Macrantha Benth. var. latifolia Hillebr.
- Stenogyne Mollis (Sherff) H. St. John
- Stenogyne Purpurea H. Mann var. brevipedunculata Wawra
- Stenogyne Purpurea H. Mann var. forbesii Sherff
- Stenogyne Purpurea H. Mann var. leptophylla Sherff
- Stenogyne Rotundifolia A. Gray var. oblonga Sherff
- Stenogyne Rugosa Benth. var. mollis Sherff
- Stenogyne Rugosa Benth. var. subulata Sherff
- Stenogyne Scandens Sherff
- Stenogyne Scrophularioides Benth. var. biflora Sherff
- Stenogyne Scrophularioides Benth. var. nelsonii (Benth.) Sherff
- Stenogyne Scrophularioides Benth. var. remyi Sherff
- Stenogyne Scrophularioides Benth. var. skottsbergii Sherff
- Stenogyne Serpens Hillebr.
- Stenogyne Sessilis Benth. var. hexantha Sherff
- Stenogyne Sessilis Benth. var. hexanthoides O. Deg. & Sherff
- Stenogyne Sessilis Benth. var. lanaiensis Sherff
- Stenogyne Sessilis Benth. var. wilkesii Sherff
- Stenogyne Sherffii O. Deg.
- Stenogyne Sororia Sherff
- Stenogyne - Stenogyne Benth.
- Stenogyne Vagans Hillebr.
- Stenolobium Caeruleum Benth.
- Stenolobium Stans (L.) Seem.
- Stenomesson - Stenomesson Herb.
- Stenomesson Variegatum (Ruiz & Pav.) J.F. Macbr.
- Stenophyllus Barbatus (Rottb.) Britton
- Stenophyllus Capillaris (L.) Britton
- Stenophyllus Carteri Britton ex Small
- Stenophyllus Ciliatifolius (Elliott) C. Mohr
- Stenophyllus Coarctatus (Elliott) Britton
- Stenophyllus Curassavicus Britton
- Stenophyllus Portoricensis Britton
- Stenophyllus Stenophyllus (Elliott) Britton, nom. inval.
- Stenophyllus Warei (Torr.) Britton
- Stenorrhynchos Michuacanus (Llave & Lex.) Schltr., orth. var.
- Stenorrhynchos Orchioides (Sw.) Lindl.
- Stenorrhynchos Speciosus (Jacq.) Rich. ex Spreng., database artifact
- Stenosiphon - Stenosiphon Spach
- Stenosiphon Virgatus Spach
- Stenostomum Acutatum DC.
- Stenostomum Coriaceum (Vahl) Griseb.
- Stenostomum Lucidum (Sw.) C.F. Gaertn.
- Stenostomum Obtusifolium (Urb.) Britton & P. Wilson
- Stenostomum Portoricense Britton & P. Wilson
- Stenostomum Sintenisii (Urb.) Britton & P. Wilson
- Stenotaphrum Micranthum (Desv.) C.E.Hubb.
- Stenotopsis Interior (Coville) Rydb.
- Stenotopsis Linearifolia (DC.) Rydb.
- Stenotopsis Linearifolia (DC.) Rydb. var. interior (Coville) H.M. Hall
- Stenotus Acaulis (Nutt.) Nutt. var. acaulis
- Stenotus Acaulis (Nutt.) Nutt. var. glabratus (D.C. Eaton) Kartesz & Gandhi
- Stenotus Andersonii Rydb.
- Stenotus Lanuginosus (A. Gray) Greene var. andersonii (Rydb.) H.M. Hall
- Stenotus Lanuginosus (A. Gray) Greene var. lanuginosus
- Stenotus Macleanii (Brandegee) A. Heller
- Stenotus Stenophyllus (A. Gray) Greene
- Stephanandra - Stephanandra Siebold & Zucc.
- Stephanomeria Carotifera Hoover
- Stephanomeria Cinerea (S.F. Blake) S.F. Blake
- Stephanomeria Coronaria Greene
- Stephanomeria Exigua Nutt. ssp. pentachaeta D.C. Eaton
- Stephanomeria Exigua Nutt. var. coronaria (Greene) Jeps.
- Stephanomeria Exigua Nutt. var. deanei J.F. Macbr.
- Stephanomeria Exigua Nutt. var. pentachaeta (D.C. Eaton) H.M. Hall
- Stephanomeria Lygodesmoides M.E. Jones
- Stephanomeria Minor (Hook.) Nutt. var. uintensis (Goodrich & S.L. Welsh) Kartesz, da
- Stephanomeria Myrioclada D.C. Eaton
- Stephanomeria Neomexicana (Greene) Cory
- Stephanomeria Pauciflora (Torr.) A. Nelson var. parishii (Jeps.) Munz
- Stephanomeria Pauciflora (Torr.) A. Nelson var. pauciflora
- Stephanomeria Spinosa (Nutt.) S. Tomb
- Stephanomeria Tenuifolia (Raf.) H.M. Hall
- Stephanomeria Tenuifolia (Raf.) H.M. Hall var. myrioclada (D.C. Eaton) Cronquist
- Stephanomeria Tenuifolia (Raf.) H.M. Hall var. uintaensis Goodrich & S.L. Welsh
- Stephanomeria Tenuifolia (Raf.) H.M. Hall var. uintensis Goodrich & S.L. Welsh, database
- Stephanomeria Virgata Benth. var. tomentosa (Greene) Munz
- Stephen's Stork's Bill - Erodium Stephenianum Willd.
- Stephens' Penstemon - Penstemon Stephensii Brandegee
- Stepladder Ginger - Costus Malortieanus H. Wendl.
- Steptoe Valley Beardtongue - Penstemon Immanifestus N.H. Holmgren
- Sterculia Ceramica R. Br.
- Sterculia Platanifolia L. f.
- Sterculia - Sterculia L.
- Sterculia - Sterculia Setigera Delile
- Sterculia - Sterculia Tragacantha Lindl.
- Sterculia - Sterculia Urens Roxb.
- Stereocaulon Albicans Th. Fr.
- Stereocaulon Arbuscula Nyl.
- Stereocaulon Capitellatum H. Magn.
- Stereocaulon Coralloides Fr.
- Stereocaulon Denudatum Flörke
- Stereocaulon Evoutoides (H. Magn.) Frey
- Stereocaulon Microscopicum (Vill.) Frey
- Stereocaulon Pseudoarbuscula Asah.
- Stereocaulon Quisquilare (Leers) Hoffm.
- Stereocaulon Subalbicans Lamb
- Stereophyllum Donnellii (Austin) Cardot ex Par.
- Stereophyllum Leucostegum (Brid.) Mitt.
- Stereophyllum Moss - Stereophyllum Mitt.
- Stereophyllum Moss - Stereophyllum Radiculosum (Hook.) Mitt.
- Stereophyllum Wrightii (Sull.) Renauld & Cardot
- Stern's Medlar - Mespilus Canescens Phipps
- Stethoma Comata (L.) Britton
- Stethoma Pectoralis (Jacq.) Raf.
- Stethoma Verticillaris (Nees) Britton, nom. utique rej.
- Steudel's Morning-glory - Ipomoea Steudelii Millsp.
- Steudner's Clover - Trifolium Steudneri Schweinf.
- Steven's Sedge - Carex Norvegica Retz. ssp. stevenii (T. Holm) A.E. Murray
- Stevens' Fiddleleaf - Nama Stevensii C.L. Hitchc.
- Stevens' Lambsquarters - Chenopodium Album L. var. stevensii Aellen
- Stevens' Panicgrass - Panicum Stevensianum Hitchc. & Chase
- Stevia Rhombifolia Kunth
- Stevia Salicifolia Cav. var. stenophylla (A. Gray) B.L. Rob.
- Stevia Serrata Cav. var. haplopappa B.L. Rob.
- Stevia Serrata Cav. var. ivifolia (Willd.) B.L. Rob.
- Stevia Stenophylla A. Gray
- Steviopsis Fendleri (A. Gray) B.L. Turner
- Stewardson's Stopper - Eugenia Stewardsonii Britton
- Stewart's Crucifixionthorn - Holacantha Stewartii C.H. Mull.
- Stewart's Gilia - Gilia Stewartii I.M. Johnst.
- Stewart's Little Walnut - Juglans Microcarpa Berl. var. stewartii (I.M. Johnst.) W. Manning
- Stewartia Pentagyna L'Hér.
- Stewartia - Stewartia L.
- Steyermark's Milkwort - Polygala Rimulicola Steyerm.
- Steyermark's Milkwort - Polygala Rimulicola Steyerm. var. rimulicola
- Steyermark's Trimezia - Trimezia Steyermarkii R.C. Foster
- Stickbush - Clerodendrum Chinense (Osb.) Mabberley
- Stickpea - Calliandra Benth.
- Stickpea - Calliandra Haematocephala Hassk.
- Stickseed - Hackelia Opiz
- Stickseed - Lappula Moench
- Sticky Blue Eyed Mary - Collinsia Rattanii A. Gray
- Sticky Blue Eyed Mary - Collinsia Rattanii A. Gray ssp. glandulosa (Howell) Pennell
- Sticky Blue Eyed Mary - Collinsia Rattanii A. Gray ssp. rattanii
- Sticky Brittlebush - Encelia Resinifera C. Clark
- Sticky Brittlebush - Encelia Resinifera C. Clark ssp. tenuifolia C. Clark
- Sticky Buckwheat - Eriogonum Viscidulum J.T. Howell
- Sticky Catchfly - Silene Caroliniana Walter
- Sticky Catchfly - Silene Caroliniana Walter ssp. caroliniana
- Sticky Centaury - Centaurium Glanduliferum (Correll) B.L. Turner
- Sticky Chickweed - Cerastium Glomeratum Thuill.
- Sticky Chinese Houses - Collinsia Tinctoria Hartw. ex Benth.
- Sticky Cinquefoil - Potentilla Glandulosa Lindl.
- Sticky Cinquefoil - Potentilla Glandulosa Lindl. ssp. glabrata (Rydb.) D.D. Keck
- Sticky Cinquefoil - Potentilla Glandulosa Lindl. ssp. glandulosa
- Sticky Cinquefoil - Potentilla Glandulosa Lindl. ssp. globosa D.D. Keck
- Sticky Cinquefoil - Potentilla Glandulosa Lindl. ssp. pseudorupestris (Rydb.) D.D. Keck
- Sticky Cinquefoil - Potentilla Glandulosa Lindl. ssp. reflexa (Greene) D.D. Keck
- Sticky Currant - Ribes Viscosissimum Pursh
- Sticky Desertsunflower - Geraea Viscida (A. Gray) S.F. Blake
- Sticky Dicranella Moss - Dicranella Stickinensis Grout
- Sticky Drymary - Drymaria Viscosa S. Watson
- Sticky Fagonbush - Fagonia Pachyacantha Rydb.
- Sticky False Gilyflower - Allophyllum Glutinosum (Benth.) A.D. Grant & V.E. Grant
- Sticky False Pimpernel - Lindernia Viscosa (Hornem.) Merr.
- Sticky Fanpetals - Sida Glutinosa Comm. ex Cav.
- Sticky Flatsedge - Cyperus Trachysanthos Hook. & Arn.
- Sticky Florestina - Florestina Tripteris DC.
- Sticky Germander - Teucrium Glandulosum Kellogg
- Sticky Gilia - Aliciella Pinnatifida (Nutt. ex A. Gray) J.M. Porter
- Sticky Goldenweed - Pyrrocoma Lucida (D.D. Keck) Kartesz & Gandhi
- Sticky Hedgehyssop - Gratiola Brevifolia Raf.
- Sticky Indian Paintbrush - Castilleja Viscidula A. Gray
- Sticky Jointvetch - Aeschynomene Viscidula Michx.
- Sticky Leaf Arnica - Arnica Ovata Greene
- Sticky Liveforever - Dudleya Viscida (S. Watson) Moran
- Sticky Lovegrass - Eragrostis Glutinosa (Sw.) Trin.
- Sticky Monkeyflower - Mimulus Viscidus Congd.
- Sticky Monkeyflower - Mimulus Viscidus Congd. ssp. constrictus (A.L. Grant) Munz
- Sticky Monkeyflower - Mimulus Viscidus Congd. ssp. viscidus
- Sticky Nightshade - Solanum Sisymbriifolium Lam.
- Sticky Oxeye - Heteranthemis Viscidehirta Schott
- Sticky Panicgrass - Homolepis Glutinosa (Sw.) F. Zuloaga & Soderstr.
- Sticky Phacelia - Phacelia Glandulifera Piper
- Sticky Phacelia - Phacelia Lenta Piper
- Sticky Phlox - Phlox Viscida E.E. Nelson
- Sticky Pincushionplant - Navarretia Viscidula Benth.
- Sticky Pincushionplant - Navarretia Viscidula Benth. ssp. purpurea (Greene) H. Mason
- Sticky Pincushionplant - Navarretia Viscidula Benth. ssp. viscidula
- Sticky Polemonium - Polemonium Viscosum Nutt.
- Sticky Purple Geranium - Geranium Viscosissimum Fisch. & C.A. Mey. ex C.A. Mey.
- Sticky Purple Geranium - Geranium Viscosissimum Fisch. & C.A. Mey. ex C.A. Mey. var. incisum (Torr. & A. Gray) N
- Sticky Purple Geranium - Geranium Viscosissimum Fisch. & C.A. Mey. ex C.A. Mey. var. viscosissimum
- Sticky Ragwort - Senecio Viscosus L.
- Sticky Rosinweed - Silphium Glutinosum J. Allison
- Sticky Sage - Salvia Glutinosa L.
- Sticky Sandspurry - Spergularia Macrotheca (Hornem.) Heynh.
- Sticky Sandspurry - Spergularia Macrotheca (Hornem.) Heynh. var. leucantha (Greene) B.L. Rob.
- Sticky Sandspurry - Spergularia Macrotheca (Hornem.) Heynh. var. longistyla R.P. Rossb.
- Sticky Sandspurry - Spergularia Macrotheca (Hornem.) Heynh. var. macrotheca
- Sticky Saw-wort - Saussurea Viscida Hultén
- Sticky Skullcap - Scutellaria Resinosa Torr.
- Sticky Snakeroot - Ageratina Adenophora (Spreng.) R.M. King & H. Rob.
- Sticky Snakeweed - Gutierrezia Texana (DC.) Torr. & A. Gray var. glutinosa (S. Schauer) M.A. Lane
- Sticky Sprangletop - Leptochloa Viscida (Scribn.) Beal
- Sticky Tansyaster - Machaeranthera Viscida (Wooton & Standl.) R.L. Hartm.
- Sticky Tofieldia - Triantha Glutinosa (Michx.) Baker
- Sticky Tofieldia - Triantha Occidentalis (S. Watson) Gates ssp. brevistyla (C.L. Hitchc.) Packer
- Sticky Tofieldia - Triantha Occidentalis (S. Watson) Gates ssp. montana (C.L. Hitchc.) Packer
- Sticky Wattle - Acacia Howittii F. Muell.
- Sticky Waxweed - Cuphea Glutinosa Cham. & Schltdl.
- Sticky Western Rosinweed - Calycadenia Multiglandulosa DC.
- Sticky Whiteleaf Manzanita - Arctostaphylos Viscida Parry
- Sticky Whiteleaf Manzanita - Arctostaphylos Viscida Parry ssp. pulchella (Howell) P.V. Wells
- Sticky Whiteleaf Manzanita - Arctostaphylos Viscida Parry ssp. viscida
- Stickybud Pritchardia - Pritchardia Viscosa Rock
- Stickyseed - Blennosperma Less.
- Stickystem Pearlwort - Sagina Maxima A. Gray
- Stickystem Pearlwort - Sagina Maxima A. Gray ssp. crassicaulis (S. Watson) Crow
- Stickystem Pearlwort - Sagina Maxima A. Gray ssp. maxima
- Stickystem Penstemon - Penstemon Glandulosus Douglas
- Stickystem Penstemon - Penstemon Glandulosus Douglas var. chelanensis (D.D. Keck) Cronquist
- Stickystem Penstemon - Penstemon Glandulosus Douglas var. glandulosus
- Stickywilly - Galium Aparine L.
- Sticta Anthraspis Ach.
- Sticta Aurata Ach.
- Sticta Canariensis (Bory) Bory ex Delise
- Sticta Crocata (L.) Ach.
- Sticta Erosa (Eschw.) Tuck.
- Sticta Hallii Tuck.
- Sticta Linita Ach.
- Sticta Oregana Tuck.
- Sticta Pulmonaria (L.) Biroli
- Sticta Verrucosa (Huds.) Fink
- Stictocardia Campanulata auct. non (L.) Merr.
- Stictocardia - Stictocardia Hallier f.
- Stiff Beargrass - Nomaphila Stricta (Vahl) Nees
- Stiff Blue-eyed Grass - Sisyrinchium Demissum Greene
- Stiff Bluestar - Amsonia Rigida Shuttlw. ex Small
- Stiff Bristle Fern - Trichomanes Rigidum Sw.
- Stiff Buttonweed - Diodia Apiculata (Willd. ex Roem. & Schult.) K. Schum.
- Stiff Clubmoss - Lycopodium Annotinum L.
- Stiff Cowbane - Oxypolis Rigidior (L.) Raf.
- Stiff Dogwood - Cornus Foemina Mill.
- Stiff Fendlerbush - Fendlera Rigida I.M. Johnst.
- Stiff Flower Star Orchid - Epidendrum Rigidum Jacq.
- Stiff Goldenrod - Oligoneuron Rigidum (L.) Small
- Stiff Goldenrod - Oligoneuron Rigidum (L.) Small var. glabratum (E.L. Braun) G.L. Nesom
- Stiff Goldenrod - Oligoneuron Rigidum (L.) Small var. humile (Porter) G.L. Nesom
- Stiff Goldenrod - Oligoneuron Rigidum (L.) Small var. rigidum
- Stiff Greenthread - Thelesperma Filifolium (Hook.) A. Gray
- Stiff Greenthread - Thelesperma Filifolium (Hook.) A. Gray var. filifolium
- Stiff Greenthread - Thelesperma Filifolium (Hook.) A. Gray var. intermedium (Rydb.) Shinners
- Stiff Hedgenettle - Stachys Recta L.
- Stiff Maiden Fern - Thelypteris Sclerophylla (Poepp. ex Spreng.) Morton
- Stiff Marsh Bedstraw - Galium Tinctorium (L.) Scop.
- Stiff Parmotrema Lichen - Parmotrema Rigidum (Lynge) Hale
- Stiff Pea - Lathyrus Rigidus T.G. White
- Stiff Phlox - Phlox Rigida Benth.
- Stiff Sedge - Carex Biltmoreana Mack.
- Stiff Shoestring Fern - Vittaria Elongata Sw.
- Stiff Star-grass - Hypoxis Rigida Chapm.
- Stiff Sunflower - Helianthus Pauciflorus Nutt.
- Stiff Sunflower - Helianthus Pauciflorus Nutt. ssp. pauciflorus
- Stiff Sunflower - Helianthus Pauciflorus Nutt. ssp. subrhomboideus (Rydb.) O. Spring & E. Schilling
- Stiff Tickseed - Coreopsis Palmata Nutt.
- Stiff Ticktrefoil - Desmodium Obtusum (Muhl. ex Willd.) DC.
- Stiff Tonguefern - Elaphoglossum Rigidum (Aubl.) Urb.
- Stiff Willowherb - Epilobium Rigidum Hausskn.
- Stiff Yellow Flax - Linum Medium (Planch.) Britton
- Stiff Yellow Flax - Linum Medium (Planch.) Britton var. medium
- Stiff Yellow Flax - Linum Medium (Planch.) Britton var. texanum (Planch.) Fernald
- Stiff Yellow Indian Paintbrush - Castilleja Lutescens (Greenm.) Rydb.
- Stiffbranch Bird's Beak - Cordylanthus Rigidus (Benth.) Jeps.
- Stiffbranch Bird's Beak - Cordylanthus Rigidus (Benth.) Jeps. ssp. brevibracteatus (A. Gray) Munz
- Stiffbranch Bird's Beak - Cordylanthus Rigidus (Benth.) Jeps. ssp. rigidus
- Stiffbranch Bird's Beak - Cordylanthus Rigidus (Benth.) Jeps. ssp. setigerus T.I. Chuang & Heckard
- Stiffhair Waxweed - Cuphea Strigulosa Kunth
- Stiffleaf Cheesewood - Pittosporum Crassifolium Banks & Sol. ex A. Cunn.
- Stiffleaf False Foxglove - Agalinis Strictifolia (Benth.) Pennell
- Stiffleaf False Goldenaster - Heterotheca Stenophylla (A. Gray) Shinners
- Stiffleaf False Goldenaster - Heterotheca Stenophylla (A. Gray) Shinners var. angustifolia (Rydb.) Semple
- Stiffleaf False Goldenaster - Heterotheca Stenophylla (A. Gray) Shinners var. stenophylla
- Stiffleaf Penstemon - Penstemon Aridus Rydb.
- Stiffleaf Scratchdaisy - Croptilon Rigidifolium (E.B. Sm.) E.B. Sm.
- Stiffpoint Jacob's-ladder - Polemonium Cuspidatum Siebold & Zucc.
- Stiffstem Flax - Linum Rigidum Pursh
- Stiffstem Flax - Linum Rigidum Pursh var. rigidum
- Stiffstem Flax - Linum Rigidum Pursh var. simulans C.M. Rogers
- Stiffstem Saxifrage - Saxifraga Hieraciifolia Waldst. & Kit. ex Willd.
- Stiffstem Saxifrage - Saxifraga Hieraciifolia Waldst. & Kit. ex Willd. var. angusticapsula Hultén
- Stiffstem Saxifrage - Saxifraga Hieraciifolia Waldst. & Kit. ex Willd. var. hieraciifolia
- Stiffstem Saxifrage - Saxifraga Hieraciifolia Waldst. & Kit. ex Willd. var. rufopilosa Hultén
- Stigmaphyllon Cordifolium Nied.
- Stigmaphyllon Ledifolium (Kunth) Small
- Stigmaphyllon Lingulatum (Poir.) Small
- Stigmaphyllon Ovatum (Cav.) Nied.
- Stigmaphyllon Periplocifolium (Desf. ex DC.) A. Juss.
- Stigmaphyllon Rubrinervum Alain
- Stigmaphyllon Tomentosum (Desf.) Nied.
- Stigmidium Atryneae (Arnold) Hafellner
- Stigmidium Congestum (Körb.) Triebel
- Stigmidium Ephebes (Henssen) D. Hawksw.
- Stigmidium Fuscatae (Arnold) R. Sant.
- Stigmidium Lichen - Stigmidium Marinum (Deakin) Swinscow
- Stigmidium Lichen - Stigmidium Psorae (Anzi) Hafellner
- Stigmidium Lichen - Stigmidium Trevis.
- Stigmidium Parva (Henssen) ?, ined.?
- Stigmidium Tabacinae (Arnold) Triebel
- Stilling's Disc Lichen - Buellia Stillingiana J. Steiner
- Stillingia Angustifolia (Müll. Arg.) Engelm. ex S. Watson
- Stillingia Salicifolia (Torr.) Raf.
- Stillingia Spathulata (Müll. Arg.) Small
- Stillingia Sylvatica L. var. linearifolia (Torr.) Müll. Arg.
- Stillingia Sylvatica L. var. salicifolia Torr.
- Stillingia Tenuis Small
- Stillman's Needlegrass - Achnatherum Stillmanii (Bol.) Barkworth
- Stillman's Tickseed - Coreopsis Stillmanii (A. Gray) S.F. Blake
- Stingbush - Eucnide Zucc.
- Stinging Annual Lupine - Lupinus Hirsutissimus Benth.
- Stinging Nettle - Urtica Dioica L.
- Stinging Nettle - Urtica Dioica L. ssp. dioica
- Stinging Nettle - Urtica Dioica L. ssp. holosericea (Nutt.) Thorne
- Stinging Phacelia - Phacelia Malvifolia Cham.
- Stinging Serpent - Cevallia Lag.
- Stinging Serpent - Cevallia Sinuata Lag.
- Stingingnettle - Hesperocnide Torr.
- Stink Currant - Ribes Bracteosum Douglas ex Hook.
- Stinkbells - Fritillaria Agrestis Greene
- Stinkgrass - Eragrostis Cilianensis (All.) Vign. ex Janchen
- Stinkgrass - Melinis P. Beauv.
- Stinking Brickellbush - Brickellia Rusbyi A. Gray
- Stinking Camphorweed - Pluchea Foetida (L.) DC.
- Stinking Camphorweed - Pluchea Foetida (L.) DC. var. foetida
- Stinking Camphorweed - Pluchea Foetida (L.) DC. var. imbricata Kearney
- Stinking Chamomile - Anthemis Cotula L.
- Stinking Goosefoot - Chenopodium Vulvaria L.
- Stinking Hawksbeard - Crepis Foetida L.
- Stinking Hawksbeard - Crepis Foetida L. var. foetida
- Stinking Hawksbeard - Crepis Foetida L. var. rhoeadifolia (M. Bieb.) Celak.
- Stinking Iris - Iris Foetidissima L.
- Stinking Juniper - Juniperus Foetidissima Willd.
- Stinking Milkvetch - Astragalus Praelongus Sheldon
- Stinking Milkvetch - Astragalus Praelongus Sheldon var. lonchopus Barneby
- Stinking Milkvetch - Astragalus Praelongus Sheldon var. praelongus
- Stinking Roger - Osteospermum Calendulaceum L. f.
- Stinking Strawflower - Helichrysum Foetidum (L.) Cass.
- Stinking Willie - Senecio Jacobaea L.
- Stinkingfish - Tetrazygia Angustifolia (Sw.) DC.
- Stinkingtoe - Hymenaea Courbaril L.
- Stinknet - Oncosiphon Piluliferum (L. f.) Källersjö
- Stinkvine - Paederia Foetida L.
- Stinkweed - Cleomella Dc.
- Stinkwood - Piscidia Carthagenensis Jacq.
- Stinkwort - Dittrichia Graveolens (L.) Greuter
- Stipa Arabica Trin. & Rupr.
- Stipa Arida M.E. Jones
- Stipa Aristella L.
- Stipa Avenacea L.
- Stipa Avenacioides Nash
- Stipa Barbata Desf.
- Stipa Bloomeri Bol.
- Stipa Brachychaeta Godr.
- Stipa Bromoides (L.) Dorfl.
- Stipa Caduca (Beal) Scribn.
- Stipa Californica Merr. & Burtt Davy
- Stipa Canadensis Poir.
- Stipa Capensis Thunb.
- Stipa Capillata L.
- Stipa Caragana Trin.
- Stipa Caucasica Schmalh. ssp. desertorum (Roshev.) Tzvelev
- Stipa Cernua Stebbins & R.M. Love
- Stipa Chaetophora (Griseb.) Columbus & J.P. Smith
- Stipa Clandestina Hack.
- Stipa Columbiana Macoun var. nelsonii (Scribn.) H. St. John
- Stipa Columbiana Macoun, nom. utique rej.
- Stipa Comata Trin. & Rupr.
- Stipa Comata Trin. & Rupr. ssp. intonsa Piper
- Stipa Comata Trin. & Rupr. var. comata
- Stipa Comata Trin. & Rupr. var. falcata B. Boivin p.p.
- Stipa Comata Trin. & Rupr. var. intermedia Scribn. & Tweedy
- Stipa Comata Trin. & Rupr. var. suksdorfii H. St. John
- Stipa Contracta (B.L. Johnson) W.A. Weber
- Stipa Coronata Thurb.
- Stipa Coronata Thurb. var. depauperata (M.E. Jones) Hitchc.
- Stipa Coronata Thurb. var. parishii (Vasey) Hitchc.
- Stipa Curtiseta (Hitchc.) Barkworth
- Stipa Curvifolia Swallen
- Stipa Desertorum (Roshev.) Ikonn.
- Stipa Diegoensis Swallen
- Stipa Divaricata Columbus & J.P. Smith
- Stipa Dregeana Steud.
- Stipa Elmeri Piper & Brodie ex Scribn.
- Stipa Eminens Cav.
- Stipa Exigua (Thurb.) Columbus & J.P. Smith
- Stipa Falcata Hughes
- Stipa Fimbriata Kunth
- Stipa Fontanesii Parl.
- Stipa Formicarum Delile
- Stipa Gigantea Link
- Stipa Glareosa P.A. Smirn.
- Stipa Haussknechtii Boiss.
- Stipa Hendersonii (Vasey) Muhl.
- Stipa Holosericea Trin. & Rupr.
- Stipa Holosericea Trin. & Rupr. ssp. fontanesii (Parl.) Tzvelev
- Stipa Hyalina Nees
- Stipa Hymenoides Roem. & Schult.
- Stipa Hypogona Hack.
- Stipa Joannis Celak.
- Stipa Juncea auct.
- Stipa Kingii Bol.
- Stipa L.
- Stipa Lagascae Roem. & Schult.
- Stipa Latiglumis Swallen
- Stipa Lemmonii (Vasey) Scribn.
- Stipa Lemmonii (Vasey) Scribn. var. jonesii Scribn.
- Stipa Lemmonii (Vasey) Scribn. var. lemmonii
- Stipa Lemmonii (Vasey) Scribn. var. pubescens Crampton
- Stipa Lepida Hitchc.
- Stipa Lepida Hitchc. var. andersonii (Vasey) Hitchc.
- Stipa Lessingiana Trin. & Rupr.
- Stipa Lettermanii Vasey
- Stipa Leucotricha Trin. & Rupr.
- Stipa Littoralis Phil.
- Stipa Lobata Swallen
- Stipa Manicata E. Desv.
- Stipa Mauritanica (Poir.) Columbus & J.P. Smith
- Stipa Megapotamica Spreng. ex Trin.
- Stipa Miliacea (L.) Hoover
- Stipa Minor (Vasey) Scribn.
- Stipa Neesiana Trin. & Rupr.
- Stipa Nelsonii Scribn.
- Stipa Nelsonii Scribn. ssp. dorei Barkworth & Maze
- Stipa Nelsonii Scribn. var. dorei (Barkworth & Maze) Dorn
- Stipa Nelsonii Scribn. var. longiaristata Barkworth & Maze
- Stipa Neomexicana (Thurb. ex J.M. Coult.) Scribn.
- Stipa Nevadensis B.L. Johnson
- Stipa Occidentalis Thurb.
- Stipa Occidentalis Thurb. var. californica (Merr. & Burtt Davy) C.L. Hitchc.
- Stipa Occidentalis Thurb. var. minor sensu C.L. Hitchc., non (Vasey) C.L. Hitchc.
- Stipa Occidentalis Thurb. var. nelsonii (Scribn.) C.L. Hitchc.
- Stipa Occidentalis Thurb. var. pubescens (Vasey) Maze, Roy L. Taylor & MacBryde
- Stipa Offneri Breistr.
- Stipa Orientalis Trin.
- Stipa Papposa Nees, nom. illeg.
- Stipa Parishii Vasey
- Stipa Perplexa (Hoge & Barkworth) Wipff & S.D. Jones
- Stipa Pinetorum M.E. Jones
- Stipa Porteri Rydb.
- Stipa Pringlei (Beal) Scribn.
- Stipa Psylantha Speg.
- Stipa Pulcherrima K. Koch
- Stipa Pulchra Hitchc.
- Stipa Purpurata (Phil.) Columbus & J.P. Smith
- Stipa Richardsonii Link
- Stipa Robusta (Vasey) Scribn.
- Stipa Sareptana A.K. Becker
- Stipa Scribneri Vasey
- Stipa Shoshoneana Curto & Douglass M. Hend.
- Stipa Spartea Trin.
- Stipa Spartea Trin. var. curtiseta Hitchc.
- Stipa Speciosa Trin. & Rupr.
- Stipa Spicata L. f.
- Stipa Splendens Trin.
- Stipa Stenophylla (Czern. ex Lindem.) Trautv.
- Stipa Stillmanii Bol.
- Stipa Szovitziana Trin. & Rupr.
- Stipa Tenuis Phil.
- Stipa Tenuissima Trin.
- Stipa Thurberiana Piper
- Stipa Tirsa Steven
- Stipa Tortilis Desf.
- Stipa Trichotoma Nees
- Stipa Ucrainica P.A. Smirn.
- Stipa Vaseyi Scribn.
- Stipa Viridula Trin.
- Stipa Webberi (Thurb.) B.L. Johnson
- Stipa Williamsii Scribn.
- Stipagrostis Ciliata (Desf.) De Winter
- Stipagrostis Lanata (Forssk.) De Winter
- Stipagrostis Nees
- Stipagrostis Obtusa (Delile) Nees
- Stipagrostis Pennata (Trin.) De Winter
- Stipagrostis Pennata (Trin.) De Winter ssp. pennata
- Stipagrostis Plumosa (L.) Munro ex T. Anderson
- Stipagrostis Uniplumis (Licht.) De Winter
- Stipagrostis Uniplumis (Licht.) De Winter var. neesii (Trin. & Rupr.) De Winter
- Stipitate Lichinella Lichen - Lichinella Stipatula Nyl.
- Stipitate Skin Lichen - Leptogium Stipitatum Vain.
- Stiporyzopsis Bloomeri (Bol.) B.L. Johnson
- Stipulate Leaf-flower - Phyllanthus Stipulatus (Raf.) G.L. Webster
- Stipulated Cinquefoil - Potentilla Stipularis L.
- Stipule Fanpetals - Sida Stipularis Cav.
- Stipulicida Filiformis Nash
- Stipulicida Lacerata (C.W. James) D.B. Poind., K.E. Bennett, & Weakley
- Stipulicida - Stipulicida Michx.
- Stirton's Bryum Moss - Bryum Stirtonii Schimp.
- Stirtonia Lichen - Stirtonia A.l. Sm.
- Stirtonia Lichen - Stirtonia Alba (Müll. Arg.) ?, ined.?
- Stitchwort - Minuartia L.
- Stizolobium Aterrimum Piper & Tracy
- Stizolobium Cinereum Piper & Tracy
- Stizolobium Deeringianum Bort
- Stizolobium Niveum (Roxb.) Kuntze
- Stizolobium Pruriens (L.) Medik.
- Stizolobium Pruritum (Wight) Piper
- Stizolobium Velutinum (Hassk.) Piper & Tracy
- Stock - Matthiola W.t. Aiton
- Stockflower Fanpetals - Sida Longipes A. Gray
- Stokes' Aster - Stokesia Laevis (Hill) Greene
- Stokesia - Stokesia L'hér.
- Stokesiella Brittoniae (Grout) H. Rob.
- Stokesiella Oregana (Sull.) H. Rob.
- Stokesiella Praelonga (Hedw.) H. Rob.
- Stokesiella Praelonga (Hedw.) H. Rob. var. californicum (Grout) H.A. Crum & L.E. Ander
- Stokesiella Praelonga (Hedw.) H. Rob. var. stokesii (Turner) H.A. Crum
- Stolon Draba - Draba Sobolifera Rydb.
- Stolon Sandwort - Minuartia Stolonifera T.W. Nelson & J.P. Nelson
- Stolon Stonecrop - Sedum Stoloniferum S.G. Gmel.
- Stolon Waterdropwort - Oenanthe Javanica (Blume) DC. ssp. stolonifera (Wall. ex DC.) Murata
- Stolonbearing Hawthorn - Crataegus Iracunda Beadle
- Stoloniferous Pussytoes - Antennaria Dioica (L.) Gaertn.
- Stomoisia Cornuta (Michx.) Raf.
- Stomoisia Juncea (Vahl) Barnhart
- Stomoisia Virgatula (Barnhart) Barnhart
- Stone Bramble - Rubus Saxatilis L.
- Stone Mountain Beaksedge - Rhynchospora Globularis (Chapm.) Small var. saxicola (Small) Kük.
- Stone Mountainmint - Pycnanthemum Curvipes (Greene) E. Grant & Epling
- Stone River Bladderpod - Lesquerella Stonensis Rollins
- Stone Rubberweed - Hymenoxys Lapidicola S.L. Welsh & Neese, nom. inq.
- Stonecrop Gilia - Aliciella Sedifolia (Brandegee) J.M. Porter
- Stonecrop - Hylotelephium H. Ohba
- Stonecrop Phacelia - Phacelia Saxicola A. Gray
- Stonecrop - Rhodiola L.
- Stonecrop - Sedum L.
- Stoneroot - Collinsonia Verticillata Baldw.
- Stoneseed - Lithospermum L.
- Stonewood - Callistemon Salignus (Sm.) Sweet
- Stool Iris - Iris Aphylla L.
- Stopper - Eugenia L.
- Storehousebush - Cudrania Tricuspidata (Carrière) Bureau ex Lavallée
- Stork's Bill - Erodium L'hér. ex Aiton
- Stork's Bill - Erodium Serpyllifolia Hose
- Storm Saxifrage - Saxifraga Tempestiva Elvander & Denton
- Storm Sedge - Carex Onusta Mack.
- Stout Goldenrod - Solidago Squarrosa Nutt.
- Stout Phacelia - Phacelia Robusta (J.F. Macbr.) I.M. Johnst.
- Stout Rush - Juncus Nodatus Coville
- Stout Smartweed - Polygonum Robustius (Small) Fernald
- Stoutstem Threadplant - Nemacladus Rigidus Curran
- Straggler Daisy - Calyptocarpus Vialis Less.
- Straggling St. Johnswort - Hypericum Dolabriforme Vent.
- Straggly Gooseberry - Ribes Divaricatum Douglas var. pubiflorum Koehne
- Straight Bladderpod - Physaria Rectipes (Wooton & Standl) O'Kane & Al-Shehbaz
- Straight Lineleaf Fern - Antrophyum Lanceolatum (L.) Kaulf.
- Straightbeak Buttercup - Ranunculus Orthorhynchus Hook.
- Straightbeak Buttercup - Ranunculus Orthorhynchus Hook. var. orthorhynchus
- Straightleaf Rush - Juncus Orthophyllus Coville
- Straitjackets - Micropsis Dc.
- Strand Tangantangan - Schleinitzia Fosbergii L.I.Nevling & Ch.J.Niezgoda
- Strand Tangantangan - Schleinitzia Warb.
- Strangospora Lichen - Strangospora A. Massal.
- Strangospora Lichen - Strangospora Microhaema (Norman) R. Anderson
- Strangospora Lichen - Strangospora Moriformis (Ach.) Stein
- Strangospora Lichen - Strangospora Ochrophora (Nyl.) R. Anderson
- Strangospora Lichen - Strangospora Pinicola (A. Massal.) Körb.
- Strangulate Orthotrichum Moss - Orthotrichum Strangulatum P. Beauv.
- Stranvaesia Niitakayamensis (Hayata) Hayata
- Strap Airplant - Catopsis Griseb.
- Strapfern - Campyloneurum C. Presl
- Strapleaf Willow - Salix Ligulifolia (C.R. Ball) C.R. Ball ex C.K. Schneid.
- Strapwort - Corrigiola Litoralis L.
- Stratiotes Alismoides L.
- Straw Foxglove - Digitalis Lutea L.
- Strawberry Cactus - Mammillaria Dioica K. Brandegee
- Strawberry Cinquefoil - Potentilla Fragiformis Willd. ex Schltdl.
- Strawberry Clover - Trifolium Fragiferum L.
- Strawberry - Fragaria L.
- Strawberry - Fragaria ×ananassa (Weston) Duchesne ex Rozier (pro sp.)
- Strawberry - Fragaria ×ananassa (Weston) Duchesne ex Rozier ssp. ananassa
- Strawberry - Fragaria ×ananassa (Weston) Duchesne ex Rozier ssp. cuneifolia (Nutt. ex Howell) St
- Strawberry - Fragaria ×bringhurstii Staudt
- Strawberry Groundcherry - Physalis Alkekengi L.
- Strawberry Guava - Psidium Cattleianum Sabine
- Strawberry Hedgehog Cactus - Echinocereus Stramineus (Engelm.) F. Seitz
- Strawberry Raspberry - Rubus Illecebrosus Focke
- Strawberry Saxifrage - Saxifragopsis Fragarioides (Greene) Small
- Strawberry Tree - Arbutus Unedo L.
- Strawberry-pear - Hylocereus Trigonus (Haw.) Saff.
- Strawberry-tomato - Physalis Grisea (Waterf.) M. Martínez
- Strawberryleaf Cinquefoil - Potentilla Sterilis (L.) Garcke
- Strawberryleaf Raspberry - Rubus Pedatus Sm.
- Strawberrytree - Muntingia Calabura L.
- Strawcolored Flatsedge - Cyperus Strigosus L.
- Strawflower - Bracteantha Anderb. & Heagi
- Strawflower - Helichrysum Mill.
- Streaked Bur Ragweed - Ambrosia Linearis (Rydb.) Payne
- Stream Bogmoss - Mayaca Fluviatilis Aubl.
- Stream Currant - Ribes Oxyacanthoides L. ssp. cognatum (Greene) Sinnott
- Stream Orchid - Epipactis Gigantea Douglas ex Hook.
- Stream-bed Cyanea - Cyanea Habenata (H. St. John) Lammers
- Streambank Bird's-foot Trefoil - Lotus Oblongifolius (Benth.) Greene
- Streambank Bird's-foot Trefoil - Lotus Oblongifolius (Benth.) Greene var. cupreus (Greene) Ottley
- Streambank Bird's-foot Trefoil - Lotus Oblongifolius (Benth.) Greene var. oblongifolius
- Streambank Bittercress - Cardamine Micranthera Rollins
- Streambank Blazingstar - Mentzelia Incisa Urb. & Gilg
- Streambank Bulrush - Schoenoplectus Triqueter (L.) Palla
- Streambank Colicwood - Myrsine Fernseei (Mez) Hosaka
- Streambank Copperleaf - Acalypha Bisetosa Bertol. ex Spreng.
- Streambank Cyanea - Cyanea Longissima (Rock) H. St. John
- Streambank Flowering Fern - Anemia Hirta (L.) Sw.
- Streambank Lipfern - Cheilanthes Paupercula (Kunze) Mett.
- Streambank Mock Orange - Philadelphus Hirsutus Nutt.
- Streambank Rabbitsfoot Grass - Polypogon Elongatus Kunth
- Streambank Spiderlily - Hymenocallis Rotata (Ker Gawl.) Herb.
- Streambank Springbeauty - Claytonia Parviflora Douglas ex Hook.
- Streambank Springbeauty - Claytonia Parviflora Douglas ex Hook. ssp. grandiflora John M. Mill. & K.L. Chambers
- Streambank Springbeauty - Claytonia Parviflora Douglas ex Hook. ssp. parviflora
- Streambank Springbeauty - Claytonia Parviflora Douglas ex Hook. ssp. utahensis (Rydb.) John M. Mill. & K.L. Cha
- Streambank Springbeauty - Claytonia Parviflora Douglas ex Hook. ssp. viridis (Davidson) John M. Mill. & K.L. Ch
- Streambank Wild Hollyhock - Iliamna Rivularis (Douglas ex Hook.) Greene
- Streambank Wild Hollyhock - Iliamna Rivularis (Douglas ex Hook.) Greene var. diversa (A. Nelson) Wiggins
- Streambank Wild Hollyhock - Iliamna Rivularis (Douglas ex Hook.) Greene var. rivularis
- Streambed Bristlegrass - Setaria Leucopila (Scribn. & Merr.) K. Schum.
- Streambed Nehe - Lipochaeta Tenuis O. Deg. & Sherff
- Streambed Phyllostegia - Phyllostegia Vestita Benth.
- Streamside Bryum Moss - Bryum Riparium I. Hagen
- Streamside Bur Cucumber - Sicyos Ampelophyllus Wooton & Standl.
- Streamside Fleabane - Erigeron Glabellus Nutt.
- Streamside Fleabane - Erigeron Glabellus Nutt. var. glabellus
- Streamside Fleabane - Erigeron Glabellus Nutt. var. pubescens Hook.
- Streamside Hygroamblystegium Moss - Hygroamblystegium Fluviatile (Hedw.) Loeske
- Streamside Leptodictyum Moss - Leptodictyum Riparium (Hedw.) Warnst.
- Streamside Map Lichen - Rhizocarpon Riparium Rasanen
- Streamside Orthotrichum Moss - Orthotrichum Rivulare Turner
- Streamside Phlox - Phlox Pilosa L. ssp. riparia Wherry
- Streamside Schistidium Moss - Schistidium Rivulare (Brid.) Podp.
- Streamside Schistidium Moss - Schistidium Rivulare (Brid.) Podp. var. rivulare
- Streamside Sphagnum - Sphagnum Riparium Ångstr.
- Streamside Swordfern - Nephrolepis Rivularis (Vahl) Mett. ex Krug
- Streblotrichum Convolutum (Hedw.) P. Beauv.
- Streblus Sandwicensis (O. Deg.) H. St. John
- Streblus - Streblus Anthropophagorum (Seem.) Corner
- Streblus - Streblus Lour.
- Streptanthella Longirostris (S. Watson) Rydb. var. derelicta J.T. Howell
- Streptanthella - Streptanthella Rydb.
- Streptanthus Amplexicaulis (S. Watson) Jeps.
- Streptanthus Amplexicaulis (S. Watson) Jeps. var. barbarae J.T. Howell
- Streptanthus Arcuatus Nutt.
- Streptanthus Arizonicus S. Watson
- Streptanthus Arizonicus S. Watson var. luteus Kearney & Peebles
- Streptanthus Brazoensis Buckley
- Streptanthus Breweri A. Gray var. breweri
- Streptanthus Breweri A. Gray var. hesperidis (Jeps.) Jeps.
- Streptanthus Californicus (S. Watson) Greene
- Streptanthus Campestris S. Watson var. bernardinus (Greene) I.M. Johnst.
- Streptanthus Coulteri (S. Watson) Greene var. lemmonii (S. Watson) Jeps.
- Streptanthus Crassicaulis Torr.
- Streptanthus Glandulosus Hook. var. albidus (Greene) Jeps.
- Streptanthus Glandulosus Hook. var. niger (Greene) Munz
- Streptanthus Glandulosus Hook. var. pulchellus (Greene) Jeps.
- Streptanthus Glaucus (S. Watson) Jeps.
- Streptanthus Heterophyllus Nutt.
- Streptanthus Inflatus (S. Watson) Greene
- Streptanthus Lemmonii (S. Watson) Jeps., non Watson, nom. illeg.
- Streptanthus Longifolius Benth.
- Streptanthus Micranthus A. Gray
- Streptanthus Obtusifolius Hook.
- Streptanthus Parryi Greene
- Streptanthus Petiolaris A. Gray
- Streptanthus Pilosus (S. Watson) Jeps.
- Streptanthus Secundus Greene
- Streptanthus Tortuosus Kellogg var. oblongus Jeps.
- Streptanthus Validus (Greene) Cory
- Streptopus Amplexifolius (L.) DC. ssp. americanus (Schult. & Schult. f.) Á. Löve & D. Löv
- Streptopus Amplexifolius (L.) DC. ssp. papillatus (Ohwi) Á. Löve & D. Löve
- Streptopus Amplexifolius (L.) DC. var. americanus Schult. & Schult. f.
- Streptopus Amplexifolius (L.) DC. var. denticulatus Fassett
- Streptopus Amplexifolius (L.) DC. var. grandiflorus Fassett
- Streptopus Amplexifolius (L.) DC. var. oreopolus (Fernald) Fassett
- Streptopus Curvipes Vail
- Streptopus Fassettii Á. Löve & D. Löve
- Streptopus Lanuginosus Michx.
- Streptopus Roseus Michx.
- Streptopus Roseus Michx. ssp. curvipes (Vail) Hultén
- Streptopus Roseus Michx. ssp. longipes (Fernald) Á. Löve & D. Löve
- Streptopus Roseus Michx. var. curvipes (Vail) Fassett
- Streptopus Roseus Michx. var. longipes (Fernald) Fassett
- Streptopus Roseus Michx. var. perspectus Fassett
- Streptopus Streptopoides (Ledeb.) Frye & Rigg ssp. brevipes (Baker) Calder & Roy L. Taylo
- Streptosolen - Streptosolen Miers
- Stretchberry - Forestiera Pubescens Nutt.
- Stretchberry - Forestiera Pubescens Nutt. var. glabrifolia Shinners
- Stretchberry - Forestiera Pubescens Nutt. var. pubescens
- Striated Broom - Cytisus Striatus (Hill) Rothm.
- Strickland's Umbrellawort - Tauschia Stricklandii (J.M. Coult. & Rose) Mathias & Constance
- Strict Blue-eyed Grass - Sisyrinchium Montanum Greene
- Strict Blue-eyed Grass - Sisyrinchium Montanum Greene var. crebrum Fernald
- Strict Blue-eyed Grass - Sisyrinchium Montanum Greene var. montanum
- Strict Forget-me-not - Myosotis Stricta Link ex Roem. & Schult.
- Strict Primrose - Primula Stricta Hornem.
- Striga Lutea Lour.
- Strigose Beard Lichen - Usnea Strigosa (Ach.) Eaton
- Strigose Beard Lichen - Usnea Strigosa (Ach.) Eaton ssp. major (Michx.) I. Tav.
- Strigose Beard Lichen - Usnea Strigosa (Ach.) Eaton ssp. rubiginea (Michx.) I. Tav.
- Strigose Beard Lichen - Usnea Strigosa (Ach.) Eaton ssp. strigosa
- Strigose Bird's-foot Trefoil - Lotus Strigosus (Nutt.) Greene
- Strigose Bird's-foot Trefoil - Lotus Strigosus (Nutt.) Greene var. hirtellus (Greene) Ottley
- Strigose Bird's-foot Trefoil - Lotus Strigosus (Nutt.) Greene var. strigosus
- Strigose Bird's-foot Trefoil - Lotus Strigosus (Nutt.) Greene var. tomentellus (Greene) Isely
- Strigose Sicklegrass - Parapholis Strigosa (Dumort.) C.E. Hubbard
- Strigula Affinis (A. Massal.) R.C. Harris
- Strigula Burmudana (Nyl.) R.C. Harris
- Strigula Connivens R.C. Harris
- Strigula Elegans (Fée) Müll. Arg.
- Strigula Griseonitens R.C. Harris
- Strigula Hypothallina R.C. Harris
- Strigula Laceribracae R.C. Harris
- Strigula Lichen - Strigula Complanata (Fée) Mont.
- Strigula Lichen - Strigula Fr.
- Strigula Lichen - Strigula Nitidula Mont.
- Strigula Lichen - Strigula Phaea (Ach.) R.C. Harris
- Strigula Lichen - Strigula Stigmatella (Ach.) R.C. Harris
- Strigula Lichen - Strigula Submuriformis (R.C. Harris) R.C. Harris
- Strigula Lichen - Strigula Sychnogonioides (Nitschke) R.C. Harris
- Strigula Lichen - Strigula Viridiseda (Nyl.) R.C. Harris
- Strigula Smaragdula Fr.
- Strigula Subelegans Vain.
- Stringleaf Clubmoss - Huperzia Filiformis (Sw.) Holub
- Stringy Stonecrop - Sedum Sarmentosum Bunge
- Striped Abobe Lily - Fritillaria Striata Eastw.
- Striped Barbados Lily - Hippeastrum Striatum (Lam.) H.E. Moore
- Striped Bladderwort - Utricularia Striata Leconte ex Torr.
- Striped Brake - Pteris Plumula Desv.
- Striped Corn Catchfly - Silene Conica L.
- Striped Cottonthorn - Tetradymia Argyraea Munz & Roos
- Striped Cream Violet - Viola Striata Aiton
- Striped Garlic - Allium Cuthbertii Small
- Striped Gentian - Gentiana Villosa L.
- Striped Hawksbeard - Crepis Zacintha (L.) Babc.
- Striped Knotweed - Polygonum Striatulum B.L. Rob.
- Striped Maple - Acer Pensylvanicum L.
- Striped Prince's Pine - Chimaphila Maculata (L.) Pursh
- Striped Rosemallow - Hibiscus Striatus Cav.
- Striped Rosemallow - Hibiscus Striatus Cav. ssp. lambertianus (Kunth) Blanch. ex Proct.
- Striped Toadflax - Linaria Repens (L.) Mill.
- Striped Twinsorus Fern - Diplazium Striatum (L.) C. Presl
- Stripeseed - Piriqueta Aubl.
- Strobilanthes Anisophylla (G. Lodd.) T. Anderson
- Strobilanthes Blume
- Strobus Strobus (L.) Small, nom. inval.
- Stroganowia - Stroganowia Kar. & Kir.
- Strombocarpa Odorata A. Gray
- Strong Bladderpod - Lesquerella Valida Greene
- Strong Quillwort - Isoetes Valida (Engelm.) Clute
- Strongbark - Bourreria P. Br.
- Strongylodon Lucidus (G. Forst.) Seem.
- Strongylodon - Strongylodon Vogel
- Strophanthus - Strophanthus Dc.
- Strophanthus - Strophanthus Sarmentosus DC.
- Strophocaulos Arvensis (L.) Small
- Strophostyles Helvula (L.) Elliott var. missouriensis (S. Watson) Britton, orth. var.
- Strophostyles Helvula (L.) Elliott, orth. var.
- Strophostyles Pauciflora (Benth.) S. Watson
- Strophostyles Umbellata (Muhl. ex Willd.) Britton var. paludigena Fernald
- Struchium - Struchium P. Br.
- Strumpfia - Strumpfia Jacq.
- Struthiopteris Exaltata (Fée) Broadh.
- Struthiopteris Lineata (Sw.) Broadh.
- Struthiopteris Polypodioides (Sw.) Trevis.
- Struthiopteris Spicant (L.) Weiss
- Struthiopteris Underwoodiana Broadh.
- Strychnine - Strychnos Toxifera Schomb. ex Benth.
- Strychnine Tree - Strychnos Nux-vomica L.
- Strychnos - Strychnos L.
- Stryphnodendron - Stryphnodendron Adstringens (Mart.) Cov.
- Stryphnodendron - Stryphnodendron Barbadetimam (Vell. Conc.) Mart.
- Stryphnodendron - Stryphnodendron Mart.
- Stuckenia Filiformis (Pers.) Börner ssp. alpinus (Blytt) Haynes, D.H. Les & M. Kral,
- Stuckenia Filiformis (Pers.) Börner var. alpina (Blytt) Dorn
- Stuckenia Filiformis (Pers.) Börner var. occidentalis (J.W. Robbins) Dorn
- Stuckenia Pectinatus (L.) Börner, database artifact
- Stuckenia Striatus (Ruiz & Pav.) Holub, database artifact
- Stuckenia Vaginatus (Turcz.) Holub, database artifact
- Stunted She-oak - Allocasuarina Nana (Sieber ex Spreng.) L.A.S. Johnson
- Sturdy Bulrush - Bolboschoenus Robustus (Pursh) Soják
- Sturdy Sedge - Carex Alma L.H. Bailey
- Sturt's Cassia - Cassia Sturtii R. Br.
- Sturt's Desert Rose - Gossypium Sturtianum J.H. Willis
- Stylisma Angustifolia (Nash) House
- Stylisma Pattersonii (Fernald & B.G. Schub.) G.N. Jones
- Stylisma Trichosanthes (Michx.) House
- Stylocline Acaulis Kellogg
- Stylocline Amphibola (A. Gray) J.T. Howell
- Stylocline Amphiloba (A. Gray) J.T. Howell, database artifact
- Stylocline Filaginea (A. Gray) A. Gray
- Stylocline Filaginea (A. Gray) A. Gray var. depressa Jeps.
- Stylodon Carolinensis (Walter) Small
- Stylodon - Stylodon Raf.
- Stylogyne - Stylogyne A. DC.
- Stylopappus Elatus Nutt.
- Stylophorum - Stylophorum Nutt.
- Stylophyllum Albidum Rose
- Stylophyllum Edule (Nutt.) Britton & Rose
- Stylophyllum Hassei Rose
- Stylophyllum Insulare Rose
- Stylophyllum Nudicaule Abrams
- Stylophyllum Orcuttii Rose
- Stylophyllum Parishii Britton
- Stylophyllum Traskiae Rose
- Stylophyllum Virens Rose
- Stylophyllum Viscidum (S. Watson) Britton & Rose
- Stylosanthes Biflora (L.) Britton, Sterns & Poggenb. var. hispidissima (Michx.) Polla
- Stylosanthes Capitata Vogel
- Stylosanthes Floridana S.F. Blake
- Stylosanthes Gracilis Kunth
- Stylosanthes Guianensis (Aubl.) Sw.
- Stylosanthes Guianensis (Aubl.) Sw. var. guianensis
- Stylosanthes Guianensis (Aubl.) Sw. var. subviscosa Benth.
- Stylosanthes Guineensis Schumach.
- Stylosanthes Juncea Micheli
- Stylosanthes Montevidensis Vogel
- Stylosanthes Mucronata Willd.
- Stylosanthes Riparia Kearney
- Stylosanthes Riparia Kearney var. setifera Fernald
- Stylosanthes Sundaica Taub.
- Stylypus Vernus Raf.
- Styphelia Douglasii (A. Gray) F. Muell. ex Skottsb.
- Styphelia Mariannensis (Kaneh.) Kaneh. & Hatus.
- Styphelia - Styphelia Sm.
- Styphelia Tameiameiae (Cham. & Schltdl.) F. Muell. var. brownii (A. Gray) H. St. John
- Styphelia Tameiameiae (Cham. & Schltdl.) F. Muell. var. hexandra Fosberg & Hosaka
- Styrax Americanus Lam. var. pulverulentus (Michx.) Perkins ex Rehder
- Styrax Californicus Torr.
- Styrax Californicus Torr. var. fulvescens Eastw.
- Styrax Officinalis L. [excluded]
- Styrax Officinalis L. ssp. fulvescens (Eastw.) R.M. Beauch.
- Styrax Officinalis L. var. californicus (Torr.) Rehder
- Styrax Officinalis L. var. fulvescens (Eastw.) Munz & I.M. Johnst.
- Styrax Officinalis L. var. redivivus (Torr.) Howard
- Styrax Platanifolius Engelm. var. stellatus Cory
- Styrax Platanifolius Engelm. var. texanus (Cory) B.L. Turner
- Styrax Platanifolius Engelm. var. youngiae (Cory) B.L. Turner
- Styrax Pulverulentus Michx.
- Styrax - Styrax Benzoin Dryand.
- Styrax Texanus Cory
- Styrax Youngiae Cory
- Suaeda Americana (Pers.) Fernald
- Suaeda Californica S. Watson var. pubescens Jeps.
- Suaeda Californica S. Watson var. taxifolia (Standl.) Munz
- Suaeda Depressa (Pursh) S. Watson var. erecta S. Watson
- Suaeda Depressa auct. non (Pursh) S. Watson
- Suaeda Duripes I.M. Johnst.
- Suaeda Fruticosa auct. non Forssk.
- Suaeda Intermedia S. Watson
- Suaeda Maritima (L.) Dumort. var. americana (Pers.) B. Boivin
- Suaeda Minutiflora S. Watson
- Suaeda Nigra J.F. Macbr.
- Suaeda Nigrescens I.M. Johnst.
- Suaeda Nigrescens I.M. Johnst. var. glabra I.M. Johnst.
- Suaeda Occidentalis (S. Watson) S. Watson
- Suaeda Prostrata Pall.
- Suaeda Ramosissima (Standl.) I.M. Johnst.
- Suaeda Richii Fernald
- Suaeda Taxifolia (Standl.) Standl. ssp. brevifolia (Standl.) Abrams
- Suaeda Torreyana S. Watson
- Suaeda Torreyana S. Watson var. ramosissima (Standl.) Munz
- Subalpine Aster - Eurybia Merita (A. Nelson) G.L. Nesom
- Subalpine Bedstraw - Galium Hypotrichium A. Gray ssp. subalpinum (Hilend & J.T. Howell) Ehrend.
- Subalpine Cryptantha - Cryptantha Crymophila I.M. Johnst.
- Subalpine Draba - Draba Subalpina Goodman & C.L. Hitchc.
- Subalpine Eyebright - Euphrasia Mollis (Ledeb.) Wettst.
- Subalpine Fir - Abies Lasiocarpa (Hook.) Nutt.
- Subalpine Fir - Abies Lasiocarpa (Hook.) Nutt. var. lasiocarpa
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. callianthemus (Greene) Cronquist
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. callianthemus (Greene) Cronquist va
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. callianthemus (Greene) Cronquist va
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. peregrinus
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. peregrinus var. dawsonii Greene
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. peregrinus var. peregrinus
- Subalpine Fleabane - Erigeron Peregrinus (Banks ex Pursh) Greene ssp. peregrinus var. thompsonii (S.F. Bl
- Subalpine Goldenbush - Ericameria Zionis (L.C. Anderson) G.L. Nesom
- Subalpine Gumweed - Grindelia Subalpina Greene
- Subalpine Gumweed - Grindelia Subalpina Greene var. erecta (A. Nelson) Steyerm.
- Subalpine Gumweed - Grindelia Subalpina Greene var. subalpina
- Subalpine Larch - Larix Lyallii Parl.
- Subalpine Larkspur - Delphinium Barbeyi (Huth) Huth
- Subalpine Lupine - Lupinus Arcticus S. Watson ssp. subalpinus (Piper & B.L. Rob.) D. Dunn
- Subalpine Mariposa Lily - Calochortus Subalpinus Piper
- Subalpine Monkeyflower - Mimulus Tilingii Regel var. caespitosus (Greene) A.L. Grant
- Subalpine Stonecrop - Sedum Lanceolatum Torr. ssp. subalpinum (Blank.) R.T. Clausen
- Subarctic Ladyfern - Athyrium Filix-femina (L.) Roth ssp. angustum (Willd.) R.T. Clausen
- Subarctic Ladyfern - Athyrium Filix-femina (L.) Roth ssp. cyclosorum (Rupr.) C. Chr.
- Submersed Rimmed Lichen - Aspicilia Submersa (Lamy) Hue
- Submersed Wart Lichen - Verrucaria Submersella Servit
- Subterranean Clover - Trifolium Subterraneum L.
- Subterranean Clover - Trifolium Subterraneum L. ssp. brachycalycinum Katzn. & Morley
- Subterranean Clover - Trifolium Subterraneum L. var. yanninicum (Katzn. & Morley) Zohary
- Subterranean Indian Breadroot - Pediomelum Hypogaeum (Nutt. ex Torr. & A. Gray) Rydb.
- Subterranean Indian Breadroot - Pediomelum Hypogaeum (Nutt. ex Torr. & A. Gray) Rydb. var. hypogaeum
- Subterranean Indian Breadroot - Pediomelum Hypogaeum (Nutt. ex Torr. & A. Gray) Rydb. var. scaposum (A. Gray) Mahler
- Subterranean Indian Breadroot - Pediomelum Hypogaeum (Nutt. ex Torr. & A. Gray) Rydb. var. subulatum (Bush) J. Grimes
- Subterranean Vetch - Vicia Sativa L. ssp. amphicarpa (L.) Batt.
- Subtropical Common Reed - Phragmites Australis (Cav.) Trin. ex Steud. ssp. berlandieri (E. Fourn.) Saltonst. &
- Subularia Aquatica L. ssp. americana G. Mulligan & Calder
- Subularia Aquatica L. ssp. mexicana G.A. Mulligan & Calder, ined.?
- Succisa Australis (Wulfen) Rchb.
- Succisa - Succisa Haller
- Succisella - Succisella G. Beck
- Succulent Owl's-clover - Castilleja Campestris (Benth.) T.I. Chuang & Heckard ssp. succulenta (Hoover) T.I. Chu
- Succulent Spiderwort - Tradescantia Crassula Link & Otto
- Suckley's Endolepis - Endolepis Dioica (Nutt.) Standl.
- Suckleya - Suckleya A. Gray
- Suckling Clover - Trifolium Dubium Sibth.
- Sudan Crowfoot Grass - Dactyloctenium Germinatum Hack.
- Sudan Raphia Palm - Raphia Sudanica A. Chev.
- Sudangrass - Sorghum Bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet & Harlan
- Sudetic Lousewort - Pedicularis Sudetica Willd.
- Sudetic Lousewort - Pedicularis Sudetica Willd. ssp. albolabiata Hultén
- Sudetic Lousewort - Pedicularis Sudetica Willd. ssp. interioides Hultén
- Sudetic Lousewort - Pedicularis Sudetica Willd. ssp. interior (Hultén) Hultén
- Sudetic Lousewort - Pedicularis Sudetica Willd. ssp. scopulorum (A. Gray) Hultén
- Sudex - Sorghum Bicolor var. bicolor × bicolor var. sudanense [unnamed hybrid]
- Suffocating Clover - Trifolium Suffocatum L.
- Suffrutescent Sandwort - Arenaria Congesta Nutt. var. suffrutescens (A. Gray) B.L. Rob.
- Sugar Apple - Annona Squamosa L.
- Sugar Maple - Acer Saccharum Marshall
- Sugar Maple - Acer Saccharum Marshall var. saccharum
- Sugar Maple - Acer Saccharum Marshall var. schneckii Rehder
- Sugar Palm - Arenga Pinnata (Wurmb) Merr.
- Sugar Pine Dwarf Mistletoe - Arceuthobium Californicum Hawksw. & Wiens
- Sugar Pine - Pinus Lambertiana Douglas
- Sugar Quillwort - Isoetes Saccharata Engelm.
- Sugar Sumac - Rhus Ovata S. Watson
- Sugarberry - Celtis Laevigata Willd.
- Sugarberry - Celtis Laevigata Willd. var. brevipes (S. Watson) Sarg.
- Sugarberry - Celtis Laevigata Willd. var. laevigata
- Sugarcane Plumegrass - Saccharum Giganteum (Walter) Pers.
- Sugarcane - Saccharum L.
- Sugarcane - Saccharum Officinarum L.
- Sugarstick - Allotropa Torr. & A. Gray
- Sugarstick - Allotropa Virgata Torr. & A. Gray ex A. Gray
- Suisun Marsh Aster - Symphyotrichum Lentum (Greene) G.L. Nesom
- Suisun Thistle - Cirsium Hydrophilum (Greene) Jeps.
- Suisun Thistle - Cirsium Hydrophilum (Greene) Jeps. var. hydrophilum
- Suksdorf Woodsorrel - Oxalis Suksdorfii Trel.
- Suksdorf's Brome - Bromus Suksdorfii Vasey
- Suksdorf's Buttercup - Ranunculus Suksdorfii A. Gray
- Suksdorf's Desertparsley - Lomatium Suksdorfii (S. Watson) J.M. Coult. & Rose
- Suksdorf's Hawthorn - Crataegus Suksdorfii (Sarg.) Kruschke
- Suksdorf's Indian Paintbrush - Castilleja Suksdorfii A. Gray
- Suksdorf's Large Camas - Camassia Leichtlinii (Baker) S. Watson ssp. suksdorfii (Greenm.) Gould
- Suksdorf's Lupine - Lupinus Suksdorfii B.L. Rob.
- Suksdorf's Milkvetch - Astragalus Pulsiferae A. Gray var. suksdorfii (Howell) Barneby
- Suksdorf's Monkeyflower - Mimulus Suksdorfii A. Gray
- Suksdorf's Silene - Silene Suksdorfii B.L. Rob.
- Suksdorf's Spikerush - Eleocharis Suksdorfiana P. Beauv.
- Suksdorfia - Suksdorfia A. Gray
- Sulcaria Lichen - Sulcaria Badia Brodo & D. Hawksw.
- Sulcaria Lichen - Sulcaria Bystrek
- Sulcaria Lichen - Sulcaria Isidiifera Brodo
- Sulla - Hedysarum Coronarium L.
- Sullivan City Flax - Linum Lundellii C.M. Rogers
- Sullivant's Coolwort - Sullivantia Sullivantii (Torr. & A. Gray) Britton
- Sullivant's Entodon Moss - Entodon Sullivantii (Müll. Hal.) Lindb.
- Sullivant's Fontinalis Moss - Fontinalis Sullivantii Lindb.
- Sullivant's Macrocoma Moss - Macrocoma Sullivantii (Müll. Hal.) Grout
- Sullivant's Pleuridium Moss - Pleuridium Sullivantii Austin
- Sullivantia Ohionis Torr. & A. Gray ex A. Gray
- Sullivantia Purpusii (Brand) Rosend.
- Sullivantia Renifolia Rosend.
- Sulphur Bamboo - Phyllostachys Sulphurea (Carrière) A. Rivière & C. Rivière
- Sulphur Beardtongue - Penstemon Attenuatus Douglas ex Lindl. var. palustris (Pennell) Cronquist
- Sulphur Buttercup - Ranunculus Sulphureus Sol. ex C.J. Phipps
- Sulphur Cinquefoil - Potentilla Recta L.
- Sulphur Clover - Trifolium Ochroleucum Huds.
- Sulphur Cosmos - Cosmos Sulphureus Cav.
- Sulphur Cup Lichen - Cladonia Sulphurina (Michx.) Fr.
- Sulphur Hot Springs Buckwheat - Eriogonum Argophyllum Reveal
- Sulphur Indian Paintbrush - Castilleja Sulphurea Rydb.
- Sulphur Knapweed - Centaurea Sulphurea Willd.
- Sulphur Lichen - Fulgensia A. Massal. & De Not.
- Sulphur Lichen - Fulgensia Fulgens (Sw.) Elenkin
- Sulphur Lupine - Lupinus Sulphureus Douglas ex Hook.
- Sulphur Marsh Marigold - Caltha Leptosepala DC. ssp. leptosepala var. sulfurea C.L. Hitchc.
- Sulphur Parmotrema Lichen - Parmotrema Sulphuratum (Nees & Flotow) Hale
- Sulphur Penstemon - Penstemon Attenuatus Douglas ex Lindl.
- Sulphur Penstemon - Penstemon Attenuatus Douglas ex Lindl. var. attenuatus
- Sulphur Sedge - Carex Lutea LeBlond
- Sulphur-flower Buckwheat - Eriogonum Polyanthum Benth.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. argus Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. aureum (Gandog.) Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. bahiiforme (Torr. & A. Gray) Jeps.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. chlorothamnus Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. cladophorum Gandog.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. cognatum (Greene) Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. covillei (Small) Munz & Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. deserticum Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. devestivum Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. dichrocephalum Gandog.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. ellipticum (Nutt.) Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. furcosum Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. hypoleium (Piper) C.L. Hitchc.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. majus Hook.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. modocense (Greene) S. Stokes
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. nevadense Gandog.
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. porteri (Small) S. Stokes
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. speciosum (E. Drew) S. Stokes
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. subaridum S. Stokes
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. umbellatum
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. vernum Reveal
- Sulphur-flower Buckwheat - Eriogonum Umbellatum Torr. var. versicolor S. Stokes
- Sumac - Rhus L.
- Sumatran Sawsedge - Mapania Sumatrana (Miq.) Benth.
- Summer Coralroot - Corallorhiza Maculata (Raf.) Raf.
- Summer Coralroot - Corallorhiza Maculata (Raf.) Raf. var. maculata
- Summer Coralroot - Corallorhiza Maculata (Raf.) Raf. var. occidentalis (Lindl.) Ames
- Summer Coralroot - Corallorhiza Maculata (Raf.) Raf. var. ozettensis E. Tisch
- Summer Farewell - Dalea Pinnata (J.F. Gmel.) Barneby
- Summer Farewell - Dalea Pinnata (J.F. Gmel.) Barneby var. pinnata
- Summer Farewell - Dalea Pinnata (J.F. Gmel.) Barneby var. trifoliata (Chapm.) Barneby
- Summer Fimbry - Fimbristylis Aestivalis (Retz.) Vahl
- Summer Grape - Vitis Aestivalis Michx.
- Summer Grape - Vitis Aestivalis Michx. var. aestivalis
- Summer Grape - Vitis Aestivalis Michx. var. bicolor Deam
- Summer Holly - Comarostaphylis Diversifolia (Parry) Greene
- Summer Holly - Comarostaphylis Diversifolia (Parry) Greene ssp. diversifolia
- Summer Holly - Comarostaphylis Diversifolia (Parry) Greene ssp. planifolia (Jeps.) G. Wallace ex Thorne
- Summer Holly - Comarostaphylis Zucc.
- Summer Lupine - Lupinus Formosus Greene
- Summer Lupine - Lupinus Formosus Greene var. formosus
- Summer Lupine - Lupinus Formosus Greene var. robustus C.P. Sm.
- Summer Milkvetch - Astragalus Hyalinus M.E. Jones
- Summer Mock Orange - Philadelphus ×insignis Carrière (pro sp.)
- Summer Pheasant's Eye - Adonis Aestivalis L.
- Summer Ragwort - Ligularia Dentata (A. Gray) H. Hara
- Summer Savory - Satureja Hortensis L.
- Summer Sedge - Carex Aestivalis M.A. Curtis ex A. Gray
- Summer Snowflake - Leucojum Aestivum L.
- Summer Snowflake - Leucojum Aestivum L. ssp. aestivum
- Summer Snowflake - Leucojum Aestivum L. ssp. pulchellum (Salisb.) Briq.
- Summer Spurge - Euphorbia Discoidalis Chapm.
- Summergrass - Alloteropsis Cimicina (L.) Stapf
- Summergrass - Alloteropsis J. Presl
- Summit Colicwood - Myrsine Degeneri Hosaka
- Summit Labordia - Labordia Fagraeoidea Gaudich.
- Summit Lupine - Lupinus Apertus A. Heller
- Sumpweed - Chorisiva Rydb.
- Sun Sedge - Carex Inops L.H. Bailey ssp. heliophila (Mack.) Crins
- Sun Spurge - Euphorbia Radians Benth.
- Sunbonnets - Leibnitzia Cass.
- Sunbonnetts - Chaptalia Vent.
- Sunbright - Phemeranthus Parviflorus (Nutt.) Kiger
- Sunburst - Pseudobahia Rydb.
- Suncup - Camissonia Link
- Sundew - Drosera L.
- Sundew - Drosera ×belezeana E.G. Camus
- Sundew - Drosera ×hybrida Macfarlane (pro sp.)
- Sundew - Drosera ×linglica Kusakabe ex R. Gauthier & Gervais
- Sundew - Drosera ×obovata Mert. & W. Koch (pro sp.)
- Sundew - Drosera ×woodii R. Gauthier & Gervais
- Sundial Lupine - Lupinus Perennis L.
- Sundial Lupine - Lupinus Perennis L. ssp. gracilis (Nutt.) D. Dunn
- Sundial Lupine - Lupinus Perennis L. ssp. perennis
- Sundial Lupine - Lupinus Perennis L. ssp. perennis var. occidentalis S. Watson
- Sundial Lupine - Lupinus Perennis L. ssp. perennis var. perennis
- Sundrops - Calylophus Spach
- Sunfacing Coneflower - Rudbeckia Heliopsidis Torr. & A. Gray
- Sunflower - Helianthus L.
- Sunflower - Helianthus ×ambiguus (A. Gray) Britton (pro sp.)
- Sunflower - Helianthus ×cinereus Torr. & A. Gray (pro sp.)
- Sunflower - Helianthus ×divariserratus R.W. Long
- Sunflower - Helianthus ×doronicoides Lam. (pro sp.)
- Sunflower - Helianthus ×glaucus Small (pro sp.)
- Sunflower - Helianthus ×intermedius R.W. Long
- Sunflower - Helianthus ×kellermanii Britton (pro sp.)
- Sunflower - Helianthus ×luxurians E.E. Watson (pro sp.)
- Sunflower - Helianthus ×orgyaloides Cockerell (pro sp.)
- Sunflower Mule-ears - Wyethia Helianthoides Nutt.
- Sunloving Phacelia - Phacelia Vallis-mortae J. Voss var. heliophila (J.F. Macbr.) J. Voss
- Sunn Hemp - Crotalaria Juncea L.
- Sunnybell - Schoenolirion Torr. ex Durand
- Sunnyside Frasera - Frasera Gypsicola (Barneby) D.M. Post
- Sunolgrass - Phalaris Coerulescens Desf.
- Sunray - Enceliopsis (a. Gray) A. Nelson
- Sunray - Rhodanthe Lindl.
- Sunset Crater Beardtongue - Penstemon Clutei A. Nelson
- Sunset Crater Blazingstar - Mentzelia Collomiae C.M. Christy
- Sunset Lupine - Lupinus Horizontalis A. Heller
- Sunset Lupine - Lupinus Horizontalis A. Heller var. horizontalis
- Sunset Lupine - Lupinus Horizontalis A. Heller var. platypetalus C.P. Sm.
- Superb Beardtongue - Penstemon Superbus A. Nelson
- Superb Porpidia Lichen - Porpidia Superba (Körb.) Hertel & Knoph
- Superb Terminalia - Terminalia Superba Engl. & Diels
- Superficial Map Lichen - Rhizocarpon Superficiale (Schaerer) Vain.
- Supine Bean - Macroptilium Supinum (Wiggins & Rollins) A. Delgado
- Supine Bluegrass - Poa Supina Schrad.
- Supine Vervain - Verbena Supina L.
- Supple Fleabane - Erigeron Supplex A. Gray
- Supplejack - Berchemia Neck. ex DC.
- Surattense Nightshade - Solanum Virginianum L.
- Surefoot Buttercup - Ranunculus Pedatifidus Sm.
- Surefoot Buttercup - Ranunculus Pedatifidus Sm. var. pedatifidus Sm. [excluded]
- Surf Thistle - Cirsium Rhothophilum S.F. Blake
- Surfgrass - Phyllospadix Hook.
- Suriana - Suriana L.
- Surinam Bulletwood - Manilkara Bidentata (A. DC.) A. Chev ssp. surinamensis (Miq.) T.D. Penn.
- Surinam Campylopus Moss - Campylopus Surinamensis Müll. Hal.
- Surinam Cherry - Eugenia Uniflora L.
- Surinamese Stickpea - Calliandra Surinamensis Benth.
- Susanville Beardtongue - Penstemon Sudans M.E. Jones
- Susanville Milkvetch - Astragalus Inversus M.E. Jones
- Sutherland Hawthorn - Crataegus Sutherlandensis Sarg.
- Sutherland's Larkspur - Delphinium Sutherlandii Warnock
- Sutherlandia Microphylla Burch. ex DC.
- Sutherlandia - Sutherlandia R. Br.
- Suzuki's Eugenia - Eugenia Suzukii Kaneh.
- Svenson's Beggarticks - Bidens Hyperborea Greene var. svensonii Fassett
- Svenson's Wildrye - Elymus Svensonii Church
- Swainsona Salsula (Pall.) Taubert
- Swallen's Curly-mesquite - Hilaria Swallenii Cory
- Swallen's Lovegrass - Eragrostis Swallenii Hitchc.
- Swallen's Needlegrass - Achnatherum Swallenii (C.L. Hitchc. & Spellenb.) Barkworth
- Swallow-wort - Cynanchum L.
- Swamp Azalea - Rhododendron Viscosum (L.) Torr.
- Swamp Bay - Persea Palustris (Raf.) Sarg.
- Swamp Bellflower - Campanula Californica (Kellogg) A. Heller
- Swamp Blackberry - Rubus Semisetosus Blanch.
- Swamp Boreal-daisy - Erigeron Elatus (Hook.) Greene
- Swamp Carex - Carex Senta Boott
- Swamp Chestnut Oak - Quercus Michauxii Nutt.
- Swamp Colicwood - Myrsine Petiolata Hosaka
- Swamp Cottonwood - Populus Heterophylla L.
- Swamp Dock - Rumex Verticillatus L.
- Swamp Doghobble - Eubotrys Racemosus (L.) Nutt.
- Swamp Flatsedge - Cyperus Distinctus Steud.
- Swamp Fly Honeysuckle - Lonicera Oblongifolia (Goldie) Hook.
- Swamp Gentian - Gentiana Douglasiana Bong.
- Swamp Hornpod - Mitreola Sessilifolia (J.F. Gmel.) G. Don
- Swamp Justiceweed - Eupatorium Paludicola E.E.Schill. & LeBlond
- Swamp Larkspur - Delphinium Uliginosum Curran
- Swamp Leather Flower - Clematis Crispa L.
- Swamp Loosestrife - Decodon Verticillatus (L.) Elliott
- Swamp Lousewort - Pedicularis Lanceolata Michx.
- Swamp Milkweed - Asclepias Incarnata L.
- Swamp Milkweed - Asclepias Incarnata L. ssp. incarnata
- Swamp Milkweed - Asclepias Incarnata L. ssp. pulchra (Ehrh. ex Willd.) Woodson
- Swamp Milkwort - Polygala Appendiculata Vell.
- Swamp Millet - Isachne Globosa (Thunb.) Kuntze
- Swamp Millet - Isachne Globosa (Thunb.) Kuntze var. globosa
- Swamp Morning-glory - Ipomoea Aquatica Forssk.
- Swamp Onion - Allium Madidum S. Watson
- Swamp Paperbark - Melaleuca Ericifolia Sm.
- Swamp Peperomia - Peperomia Expallescens C. DC.
- Swamp Pricklegrass - Crypsis Schoenoides (L.) Lam.
- Swamp Rose - Rosa Palustris Marshall
- Swamp Rosemallow - Hibiscus Grandiflorus Michx.
- Swamp Rush - Juncus Paludosus E.L. Bridges & Orzell
- Swamp Saltbush - Atriplex Amnicola Paul G. Wilson
- Swamp Sawgrass - Cladium Mariscus (L.) Pohl
- Swamp Smartweed - Polygonum Hydropiperoides Michx.
- Swamp Snakeherb - Dyschoriste Humistrata (Michx.) Kuntze
- Swamp Stonecrop - Crassula Helmsii A. Berger
- Swamp Sunflower - Helianthus Angustifolius L.
- Swamp Taro - Cyrtosperma Chamissonis (Schott) Merr.
- Swamp Thistle - Cirsium Muticum Michx.
- Swamp Tickseed - Coreopsis Palustris Sorrie
- Swamp Titi - Cyrilla Racemiflora L.
- Swamp Tupelo - Nyssa Biflora Walter
- Swamp Verbena - Verbena Hastata L.
- Swamp Verbena - Verbena Hastata L. var. hastata
- Swamp Verbena - Verbena Hastata L. var. scabra Moldenke
- Swamp Vine Fern - Stenochlaena Palustris (Burm. f.) Bedd.
- Swamp Wallaby Grass - Amphibromus Scabrivalvis (Trin.) Swallen
- Swamp Wedgescale - Sphenopholis Pensylvanica (L.) Hitchc.
- Swamp White Oak - Quercus Bicolor Willd.
- Swamp-oak - Casuarina Obesa Miq.
- Swamp-redwood - Erythroxylum Areolatum L.
- Swampbush - Pavonia Paludicola Nicolson ex Fryxell
- Swampfire - Sarcocornia A.j. Scott
- Swampforest Beaksedge - Rhynchospora Decurrens Chapm.
- Swampforest Clermontia - Clermontia Waimeae Rock
- Swamplily - Crinum L.
- Swampmahogany - Eucalyptus Robusta Sm.
- Swampmallow - Pavonia Cav.
- Swamppink - Helonias Bullata L.
- Swampprivet - Forestiera Poir.
- Swampweed - Hygrophila R. Br.
- Swampwort - Enydra Lour.
- Swan's Sedge - Carex Swanii (Fernald) Mack.
- Swanflower - Aristolochia Erecta L.
- Swartz's Flatsedge - Cyperus Swartzii (A. Dietr.) Boeckeler ex Kük.
- Swartz's Jamaican Broom - Chamaecrista Glandulosa (L.) Greene var. swartzii (Wikstr.) Irwin & Barneby
- Swartz's Leafystem Orchid - Dichaea Pendula (Aubl.) Cogn.
- Swartz's Pigeonplum - Coccoloba Swartzii Meisn.
- Swartz's Polytrichum Moss - Polytrichum Swartzii Hartm.
- Swartz's Snoutbean - Rhynchosia Swartzii (Vail) Urb.
- Swartz's Threeawn - Aristida Swartziana Steud.
- Swartzia Grandiflora (Sw.) J.F. Gmel.
- Swartzia Longiflora (Tussac) Britton & P. Wilson
- Swaying Bulrush - Schoenoplectus Subterminalis (Torr.) Soják
- Sweet Acacia - Acacia Suaveolens (Sm.) Willd.
- Sweet Acacia - Vachellia Farnesiana (L.) Wight & Arn.
- Sweet After Death - Achlys Triphylla (Sm.) DC.
- Sweet Almond - Prunus Dulcis (Mill.) D.A. Webb
- Sweet Alyssum - Lobularia Maritima (L.) Desv.
- Sweet Autumn Virginsbower - Clematis Terniflora DC.
- Sweet Autumn Virginsbower - Clematis Terniflora DC. var. terniflora
- Sweet Basil - Ocimum Basilicum L.
- Sweet Bay - Laurus Nobilis L.
- Sweet Birch - Betula Lenta L.
- Sweet Boronia - Boronia Megastigma Nees ex Bartling
- Sweet Breath Of Spring - Lonicera Fragrantissima Lindl. & Paxton
- Sweet Cherry - Prunus Avium (L.) L.
- Sweet Coneflower - Rudbeckia Subtomentosa Pursh
- Sweet Crab Apple - Malus Coronaria (L.) Mill.
- Sweet Fennel - Foeniculum Vulgare Mill.
- Sweet Fern - Comptonia L'hér. ex Aiton
- Sweet Fern - Comptonia Peregrina (L.) J.M. Coult.
- Sweet Four O'clock - Mirabilis Longiflora L.
- Sweet Four O'clock - Mirabilis Longiflora L. var. longiflora L. [excluded]
- Sweet Four O'clock - Mirabilis Longiflora L. var. wrightiana (A. Gray ex Britton & Kearney) Kearney & Peeb
- Sweet Granadilla - Passiflora Ligularis Juss.
- Sweet Iris - Iris Pallida Lam.
- Sweet Marjoram - Origanum Majorana L.
- Sweet Michelia - Michelia Doltsopa Buch.-Ham. ex DC.
- Sweet Mock Orange - Philadelphus Coronarius L.
- Sweet Mountain Grape - Vitis Monticola Buckley
- Sweet Orange - Citrus ×sinensis (L.) Osbeck (pro sp.)
- Sweet Osmanthus - Osmanthus Fragrans Lour.
- Sweet Pitcherplant - Sarracenia Rubra Walter
- Sweet Pitcherplant - Sarracenia Rubra Walter ssp. rubra
- Sweet Sagewort - Artemisia Annua L.
- Sweet Scented Geranium - Pelargonium Graveolens L'Hér. ex Aiton
- Sweet Shaggytuft - Stenandrium Dulce (Cav.) Nees
- Sweet Shaggytuft - Stenandrium Dulce (Cav.) Nees var. dulce
- Sweet Shaggytuft - Stenandrium Dulce (Cav.) Nees var. floridanum A. Gray
- Sweet Signalgrass - Brachiaria Eruciformis (Sm.) Griseb.
- Sweet Tanglehead - Heteropogon Melanocarpus (Elliott) Elliott ex Benth.
- Sweet Vernalgrass - Anthoxanthum Odoratum L.
- Sweet Vernalgrass - Anthoxanthum Odoratum L. ssp. odoratum
- Sweet Violet - Viola Odorata L.
- Sweet Wakerobin - Trillium Vaseyi Harbison
- Sweet White Violet - Viola Blanda Willd.
- Sweet White Violet - Viola Blanda Willd. var. blanda
- Sweet White Violet - Viola Blanda Willd. var. palustriformis A. Gray
- Sweet William Silene - Silene Armeria L.
- Sweet Woodreed - Cinna Arundinacea L.
- Sweet Yellowcrown - Proustia Vanillosma C. Wright
- Sweet-amber - Hypericum Androsaemum L.
- Sweet-nancy - Achillea Ageratum L.
- Sweet-smelling Monardella - Monardella Beneolens Shevock, Ertter & Jokerst
- Sweetbay - Magnolia Virginiana L.
- Sweetberry Honeysuckle - Lonicera Caerulea L.
- Sweetbriar Rose - Rosa Rubiginosa L.
- Sweetbush - Bebbia (benth.) Greene
- Sweetbush - Bebbia Juncea (Benth.) Greene
- Sweetbush - Bebbia Juncea (Benth.) Greene var. aspera (Benth.) Greene
- Sweetbush - Bebbia Juncea (Benth.) Greene var. juncea (Benth.) Greene [excluded]
- Sweetcicely - Osmorhiza Berteroi DC.
- Sweetclover - Melilotus Mill.
- Sweetclover - Melilotus Officinalis (L.) Lam.
- Sweetclover - Melilotus Suaveolens Ledeb.
- Sweetclover - Melilotus Wolgicus Poir.
- Sweetclover Vetch - Vicia Pulchella Kunth
- Sweetflag - Acorus Americanus (Raf.) Raf.
- Sweetflag - Acorus L.
- Sweetflower Rockjasmine - Androsace Chamaejasme Wulfen
- Sweetflower Rockjasmine - Androsace Chamaejasme Wulfen ssp. carinata (Torr.) Hultén
- Sweetgale - Myrica Gale L.
- Sweetgale - Myrica L.
- Sweetgrass - Hierochloe Odorata (L.) P. Beauv.
- Sweetgrass - Hierochloe R. Br.
- Sweetgum - Liquidambar L.
- Sweetgum - Liquidambar Styraciflua L.
- Sweetjuice - Glinus L.
- Sweetleaf - Symplocos Jacq.
- Sweetpea - Lathyrus Odoratus L.
- Sweetpepperbush - Clethra L.
- Sweetpitted Grass - Bothriochloa Insculpta (Hochst.) A. Camus [excluded]
- Sweetpotato Cactus - Cereus Mill.
- Sweetpotato - Ipomoea Batatas (L.) Lam.
- Sweetroot - Osmorhiza Raf.
- Sweetroot Springparsley - Cymopterus Newberryi (S. Watson) M.E. Jones
- Sweetscent - Pluchea Odorata (L.) Cass.
- Sweetscent - Pluchea Odorata (L.) Cass. var. odorata
- Sweetscent - Pluchea Odorata (L.) Cass. var. succulenta (Fernald) Cronquist
- Sweetscented Bedstraw - Galium Odoratum (L.) Scop.
- Sweetscented Biscuitroot - Lomatium Serpentinum (M.E. Jones) Mathias
- Sweetscented Joe Pye Weed - Eutrochium Purpureum (L.) E.E. Lamont
- Sweetscented Joe Pye Weed - Eutrochium Purpureum (L.) E.E. Lamont var. purpureum
- Sweetscented Marigold - Tagetes Lucida Cav.
- Sweetscented Phacelia - Phacelia Suaveolens Greene
- Sweetscented Phacelia - Phacelia Suaveolens Greene ssp. suaveolens
- Sweetscented Pigeonwings - Clitoria Fragrans Small
- Sweetshoot Bamboo - Phyllostachys Dulcis McClure
- Sweetshrub - Calycanthus L.
- Sweetspire - Itea L.
- Sweetsultan - Amberboa Moschata (L.) DC.
- Sweetvetch - Hedysarum L.
- Sweetvetch - Hedysarum Mongolicum Turcz.
- Sweetvetch - Hedysarum Scoparium Fisch. & C.A. Mey.
- Sweetwater Draba - Draba Incrassata (Rollins) Rollins & R.A. Price
- Sweetwilliam - Dianthus Barbatus L.
- Sweetwood - Nectandra Membranacea (Sw.) Griseb.
- Sweetwood - Nectandra Roland. ex Rottb.
- Sweetwood - Ocotea Aubl.
- Sweginzow's Rose - Rosa Sweginzowii Koehne
- Swertia Albicaulis (Douglas ex Griseb.) Kuntze
- Swertia Albicaulis (Douglas ex Griseb.) Kuntze var. albicaulis
- Swertia Albicaulis (Douglas ex Griseb.) Kuntze var. columbiana (H. St. John) J. Pri
- Swertia Albicaulis (Douglas ex Griseb.) Kuntze var. cusickii (A. Gray) J. Pringle
- Swertia Albicaulis (Douglas ex Griseb.) Kuntze var. idahoensis (H. St. John) J. Pri
- Swertia Albicaulis (Douglas ex Griseb.) Kuntze var. nitida (Benth.) Jeps.
- Swertia Albomarginata (S. Watson) Kuntze
- Swertia Albomarginata (S. Watson) Kuntze ssp. purpusii (Jeps.) A.E. Murray
- Swertia Bethelii H. St. John
- Swertia Californica H. St. John
- Swertia Caroliniensis (Walter) Kuntze
- Swertia Coloradensis C.M. Rogers
- Swertia Columbiana H. St. John
- Swertia Cusickii (A. Gray) H. St. John
- Swertia Eastwoodiae H. St. John
- Swertia Fastigiata Pursh
- Swertia Gypsicola Barneby
- Swertia Idahoensis H. St. John
- Swertia Lassenica H. St. John
- Swertia Modocensis H. St. John
- Swertia Modocensis H. St. John var. adglabra H. St. John
- Swertia Montana (Mulford) H. St. John
- Swertia Neglecta (H.M. Hall) Jeps.
- Swertia Nitida (Benth.) Jeps.
- Swertia Nitida (Benth.) Jeps. ssp. cusickii (A. Gray) Abrams
- Swertia Pahutensis (Reveal) J. Pringle
- Swertia Parryi (Torr.) Kuntze
- Swertia Perennis L. var. obtusa (Ledeb.) Ledeb. ex Griseb.
- Swertia Puberulenta (Davidson) Jeps.
- Swertia Radiata (Kellogg) Kuntze
- Swertia Radiata (Kellogg) Kuntze var. macrophylla (Greene) H. St. John
- Swertia Recurva Sm., nom. utique rej.
- Swertia Shastensis H. St. John
- Swertia Sierrae H. St. John
- Swertia Tubulosa (Coville) Jeps.
- Swertia Umpquaensis (M. Peck & Applegate) H. St. John
- Swertia Usambarensis Engl.
- Swertia Utahensis (M.E. Jones) H. St. John
- Swertia Watsonii H. St. John
- Swida Alternifolia (L. f.) Small
- Swida Amomum (Mill.) Small
- Swida Amomum (Mill.) Small var. schuetzeana (C.A. Mey.) A.Haines
- Swida Asperifolia (Michx.) Small
- Swida Foemina (Mill.) Rydb.
- Swida Instolonea (A. Nelson) Rydb.
- Swida Microcarpa (Nash) Small
- Swida Priceae (Small) Small
- Swida Racemosa (Lam.) Moldenke
- Swida Rugosa (Lam.) Rydb.
- Swida Sanguinea (L.) Opiz
- Swida Sericea (L.) Holub
- Swida Stolonifera (Michx.) Rydb.
- Swida Stricta (Lam.) Small
- Swida Suecica (L.) Holub
- Swida ×arnoldiana (Rehder) Soják
- Swida ×friedlanderi (W.H. Wagner) Holub
- Swinecress - Coronopus Zinn
- Swinscow's Parmelinopsis - Parmelinopsis Swinscowii (Hale) Elix & Hale
- Swiss Kidney Lichen - Nephroma Helveticum Ach.
- Swiss Kidney Lichen - Nephroma Helveticum Ach. ssp. helveticum
- Swiss Stone Pine - Pinus Cembra L.
- Switchcane - Arundinaria Tecta (Walter) Muhl.
- Switchgrass - Panicum Virgatum L.
- Switchgrass - Panicum Virgatum L. var. spissum Linder
- Switchgrass - Panicum Virgatum L. var. virgatum
- Swizzlestick Tree - Quararibea Turbinata (Sw.) Poir.
- Swollen Bladderwort - Utricularia Inflata Walter
- Swollen Duckweed - Lemna Gibba L.
- Swollen Fingergrass - Chloris Barbata Sw.
- Swollen Penstemon - Penstemon Rydbergii A. Nelson var. rydbergii
- Sword Groundcherry - Physalis Lanceolata Michx.
- Sword Jackbean - Canavalia Gladiata (Jacq.) DC.
- Sword Townsend Daisy - Townsendia Spathulata Nutt.
- Swordbush - Phyllanthus Epiphyllanthus L.
- Swordfern - Macrothelypteris Torresiana (Gaudich.) Ching
- Swordfern - Nephrolepis Schott
- Swordfern - Nephrolepis ×averyi C.E. Nauman
- Swordfern - Nephrolepis ×copelandii W.H. Wagner
- Swordfern - Nephrolepis ×medlerae W.H. Wagner
- Swordleaf Blue-eyed Grass - Sisyrinchium Chilense Hook.
- Swordleaf Phlox - Phlox Buckleyi Wherry
- Swordleaf Rush - Juncus Ensifolius Wikstr.
- Syagrus Romanzoffianum (Cham.) Glassman, orth. var.
- Syagrus - Syagrus Mart.
- Sycamore Fig - Ficus Sycomorus L.
- Sycamore Maple - Acer Pseudoplatanus L.
- Sycamore Muhly - Muhlenbergia Elongata Scribn. ex Beal
- Sycamore - Platanus L.
- Sycamoreleaf Snowbell - Styrax Platanifolius Engelm.
- Sycamoreleaf Snowbell - Styrax Platanifolius Engelm. ssp. platanifolius
- Sycamoreleaf Snowbell - Styrax Platanifolius Engelm. ssp. stellatus (Cory) P.W. Fritsch
- Sydney Bluegum - Eucalyptus Saligna Sm.
- Sydney Golden Wattle - Acacia Longifolia (Andrews) Willd.
- Sydney Peppermint-tree - Eucalyptus Piperita Sm.
- Syes Butte Plainsmustard - Schoenocrambe Barnebyi (S.L. Welsh & N.D. Atwood) Rollins
- Sylvan Scorzonella - Microseris Sylvatica (Benth.) Sch. Bip.
- Symblepharis Helicophylla Mont.
- Symblepharis Moss - Symblepharis Mont.
- Symblepharis Moss - Symblepharis Vaginata (Hook.) Wijk & Margad.
- Symblepharis Raui (Austin) R.S. Williams
- Symmetric Sanionia Moss - Sanionia Uncinata (Hedw.) Loeske var. symmetrica (Renauld & Cardot) H.A. Crum & L.
- Sympetaleia Rupestris (Baill.) A. Gray ex S. Watson
- Symphoricarpos Albus (L.) S.F. Blake ssp. laevigatus (Fernald) Hultén
- Symphoricarpos Albus (L.) S.F. Blake var. mollis (Nutt.) D.D. Keck
- Symphoricarpos Albus (L.) S.F. Blake var. pauciflorus (W.J. Rob. ex A. Gray) S.F. Bla
- Symphoricarpos Mollis Nutt. ssp. hesperius (G.N. Jones) Abrams ex Ferris
- Symphoricarpos Mollis Nutt. var. acutus A. Gray
- Symphoricarpos Mollis Nutt. var. hesperius (G.N. Jones) Cronquist
- Symphoricarpos Oreophilus A. Gray var. parishii (Rydb.) Cronquist
- Symphoricarpos Parishii Rydb.
- Symphoricarpos Pauciflorus W.J. Rob. ex A. Gray
- Symphoricarpos Racemosus Michx.
- Symphoricarpos Rivularis Suksd.
- Symphoricarpos Rotundifolius A. Gray var. oreophilus (A. Gray) M.E. Jones
- Symphoricarpos Symphoricarpos (L.) MacMill., nom. inval.
- Symphoricarpos Tetonensis A. Nelson
- Symphoricarpos Utahensis Rydb.
- Symphoricarpos Vaccinioides Rydb.
- Symphyotrichum Bracteolatum (Nutt.) G.L. Nesom
- Symphyotrichum Bracteolatum auct. non (Nutt.) G.L. Nesom p.p.
- Symphyotrichum Chapmanii (Torr. & A. Gray) Semple & Brouillet
- Symphyotrichum Ciliolatum (Lindl.) Á. Löve & D. Löve var. comatum (Fernald) G.L. Nesom
- Symphyotrichum Ciliolatum (Lindl.) Á. Löve & D. Löve var. maccallae (Rydb.) G.L. Nesom
- Symphyotrichum Ciliolatum (Lindl.) Á. Löve & D. Löve var. wilsonii (Rydb.) G.L. Nesom
- Symphyotrichum Cordifolium (L.) G.L. Nesom var. furbishiae (Fernald) G.L. Nesom
- Symphyotrichum Cordifolium (L.) G.L. Nesom var. lanceolatum (Porter) G.L. Nesom
- Symphyotrichum Cordifolium (L.) G.L. Nesom var. moratum (Shinners) G.L. Nesom
- Symphyotrichum Cordifolium (L.) G.L. Nesom var. polycephalum (Porter) G.L. Nesom
- Symphyotrichum Cordifolium (L.) G.L. Nesom var. racemiflorum (Fernald) G.L. Nesom
- Symphyotrichum Crenifolium (Fernald) G.L. Nesom
- Symphyotrichum Drummondii (Lindl.) G.L. Nesom var. parviceps (Shinners) G.L. Nesom
- Symphyotrichum Dumosum (L.) G.L. Nesom var. dodgei (Fernald) G.L. Nesom
- Symphyotrichum Elliotii (Torr. & A. Gray) G.L. Nesom, database artifact
- Symphyotrichum Ericoides (L.) G.L. Nesom var. prostratum (Kuntze) G.L. Nesom
- Symphyotrichum Falcatum (Lindl.) G.L. Nesom var. crassulum (Rydb.) G.L. Nesom
- Symphyotrichum Firmum (Nees) G.L. Nesom
- Symphyotrichum Foliaceum (Lindl. ex DC.) G.L. Nesom var. cusickii (A. Gray) Lesica
- Symphyotrichum Hesperium (A. Gray) Á. Löve & D. Löve
- Symphyotrichum Lateriflorum (L.) Á. Löve & D. Löve var. hirsuticaule (Lindl. ex DC.) G.L. Ne
- Symphyotrichum Longifolium (Lam.) G.L. Nesom, as to type
- Symphyotrichum Longifolium sensu G.L. Nesom, non Lam.
- Symphyotrichum Novi-belgii (L.) G.L. Nesom var. litoreum (A. Gray) G.L. Nesom
- Symphyotrichum Novi-belgii (L.) G.L. Nesom var. tardiflorum (L.) G.L. Nesom
- Symphyotrichum Ontarione (Wiegand) G.L. Nesom var. glabratum (Semple) L. Brouillet & Bouc
- Symphyotrichum Ontarione (Wiegand) G.L. Nesom, orth. var.
- Symphyotrichum Ontarionis (Wiegand) G.L. Nesom var. glabratum (Semple) L. Brouillet & Bouc
- Symphyotrichum Patens (Aiton) G.L. Nesom var. terranigrum J.J.N. Campb. & W.R. Seymour
- Symphyotrichum Praealtum (Poir.) G.L. Nesom var. texicola (Wiegand) G.L. Nesom
- Symphyotrichum Puniceum (L.) Á. Löve & D. Löve var. calderi (B. Boivin) G.L. Nesom
- Symphyotrichum Racemosum (Elliott) G.L. Nesom var. subdumosum (Wiegand) G.L. Nesom, nom.
- Symphyotrichum Sagittifolium (Wedemeyer ex Willd.) G.L. Nesom
- Symphyotrichum Simplex (Willd.) Á. Löve & D. Löve
- Symphyotrichum Spathulatum (Lindl.) G.L. Nesom var. fremontii (Torr. & A. Gray) G.L. Nesom
- Symphyotrichum Subgeminatum (Fernald) G.L. Nesom
- Symphyotrichum Vahlii (Gaudich.) G.L. Nesom
- Symphyotrichum Vahlii (Gaudich.) G.L. Nesom var. vahlii
- Symphyotrichum ×salignum (Willd.) G.L. Nesom [excluded]
- Symphyotrichum ×versicolor (Willd.) G.L. Nesom [excluded]
- Symphysia - Symphysia C. Presl
- Symphytum Asperrimum Donn ex Sims
- Symphytum Officinale L. ssp. uliginosum auct. non (Kern.) Nyman
- Symphytum Peregrinum auct. non Ledeb.
- Symphytum Uliginosum auct. non Kern.
- Symplocos Palauensis Koidz.
- Symplocos Polyantha Krug & Urb.
- Symplocos Tinctoria (L.) L'Hér. var. ashei Harbison
- Symplocos Tinctoria (L.) L'Hér. var. pygmaea Fernald
- Synalissa Lichen - Synalissa Fr.
- Synalissa Lichen - Synalissa Symphorea (Ach.) Nyl.
- Synalissa Melambola Tuck.
- Synalissa Ramulosa (Hoffm.) Fr.
- Synalissa Subnigra (de Lesd.) Henssen
- Synalissa Texana Tuck.
- Synandra - Synandra Nutt.
- Syndesmon Thalictroides (L.) Hoffmanns. ex Britton
- Synechoblastus Aggregatus (Ach.) Th. Fr.
- Synechoblastus Polycarpus (Hoffm.) Dalla Torre & Sarnth.
- Synechoblastus Pycnocarpus Nyl.
- Synechoblastus Rupestris (Sw.) Trevis.
- Synechoblastus Texanus (Tuck.) Müll. Arg.
- Synechoblastus Wyomingensis Fink
- Synedrella - Synedrella Gaertn.
- Synedrella Vialis (Less.) A. Gray
- Synedrellopsis Grisebachii auct. non Hieron. & Kuntze
- Synelcosciadium Boiss.
- Synelcosciadium Carmelii (Labill.) Boiss. [excluded]
- Syngonanthus - Syngonanthus Ruhl.
- Syngonium Podophyllum Schott var. albolineatum Engelm.
- Syngonium - Syngonium Schott
- Syngramma - Syngramma J. Sm.
- Synosma Suaveolens (L.) Raf. ex Britton
- Synsepalum - Synsepalum (a. DC.) Daniell
- Synsepalum - Synsepalum Stipulatum (Radlk.) Engl.
- Syntherisma Argillacea Hitchc. & Chase
- Syntherisma Chinensis (Nees) Hitchc.
- Syntherisma Digitata (Sw.) Hitchc.
- Syntherisma Filiformis (L.) Nash
- Syntherisma Floridana (Hitchc.) Hitchc.
- Syntherisma Gracillima (Scribn.) Nash
- Syntherisma Ischaemum (Schreb.) Nash
- Syntherisma Marginata (Link) Nash
- Syntherisma Panicea (Sw.) Nash
- Syntherisma Pauciflora (Hitchc.) Hitchc.
- Syntherisma Sanguinalis (L.) Dulac
- Syntherisma Serotina Walter
- Syntherisma Simpsonii (Vasey) Nash
- Syntherisma Villosa Walter
- Synthlipsis - Synthlipsis A. Gray
- Synthyris Alpina A. Gray
- Synthyris Bullii (Eaton) A. Heller
- Synthyris Cymopteroides Pennell
- Synthyris Dissecta Rydb.
- Synthyris Hendersonii Pennell
- Synthyris Laciniata (A. Gray) Rydb. ssp. ibapahensis Pennell
- Synthyris Lanuginosa (Piper) Pennell & J.W. Thomp.
- Synthyris Missurica (Raf.) Pennell var. major (Hook.) Pennell ex R.J. Davis
- Synthyris Paysonii Pennell & L.O. Williams
- Synthyris Pinnatifida S. Watson var. laciniata A. Gray
- Synthyris Reniformis (Douglas ex Benth.) Benth. var. major Hook.
- Synthyris Ritteriana Eastw.
- Synthyris Rubra (Douglas ex Hook.) Benth.
- Synthyris Stellata Pennell
- Syntrichia Agraria (Hedw.) F. Weber & D. Mohr
- Syntrichia Ruralis (Hedw.) F. Weber & D. Mohr
- Syrian Acanthus - Acanthus Syriacus Boiss.
- Syrian Beancaper - Zygophyllum Fabago L.
- Syrian Cephalaria - Cephalaria Syriaca (L.) Scrad. ex Roem. & Schult.
- Syrian Juniper - Juniperus Drupacea Labill.
- Syrian Knapweed - Centaurea Babylonica (L.) L.
- Syrian Mesquite - Prosopis Farcta (Banks & Sol.) J.F. Macbr.
- Syrian Mustard - Euclidium Syriacum (L.) W.T. Aiton
- Syrian Pea - Pisum Syriacum (A. Berger) Lehman
- Syrian-privet - Fontanesia Phillyreoides Labill.
- Syrian-privet - Fontanesia Phillyreoides Labill. ssp. fortunei (Carrière) Yaltirik
- Syringa Amurensis Rupr.
- Syringa Amurensis Rupr. var. japonica (Maxim.) Franch. & Sav.
- Syringa Emodi Wall. ex G. Don
- Syringa Komarowii C.K. Schneid.
- Syringa Meyeri C.K. Schneid.
- Syringa Microphylla Diels
- Syringa Oblata Lindl.
- Syringa Oblata Lindl. ssp. dilatata (Nakai) P.S. Green & M.C. Chang
- Syringa Palibiniana Nakai
- Syringa Pubescens Turcz.
- Syringa Pubescens Turcz. ssp. microphylla (Diels) M.C. Chang & X.L. Chen
- Syringa Pubescens Turcz. ssp. patula (Palib.) M.C. Chang & X.L. Chen
- Syringa Reticulata (Blume) H. Hara ssp. pekinensis (Rupr.) P.S. Greene & M.C. Chang
- Syringa Reticulata (Blume) H. Hara var. mandschurica (Maxim.) H. Hara
- Syringa Sweginzowii Koehne & Lingelsh.
- Syringa Wolfii C.K. Schneid.
- Syringa ×josiflexa I. Preston ex J.S. Pringle
- Syringa ×prestoniae McKelvey
- Syringodium Filiforme Kütz.
- Syringodium Isoetifolium (Asch.) Dandy
- Syringodium Kütz.
- Syrrhopodon Filigerus R.S. Williams
- Syrrhopodon Floridanus Sull.
- Syrrhopodon Moss - Syrrhopodon Prolifer Schwägr.
- Syrrhopodon Moss - Syrrhopodon Schwägr.
- Syzygium Cleistocalyx (Merr.) P.S. Ashton
- Syzygium Jambolanum (Lam.) DC.
- Syzygium Ponapense (Merr. & Kaneh.) Diels
- Syzygium - Syzygium P. Br. ex Gaertn.
- Syzygium - Syzygium Samarangense (Blume) Merr. & L.M. Perry
- Syzygium - Syzygium Stelechanthum (Diels) Glassman
- Syzygospora Bachmannii Diederich & M.S. Christ.
- Syzygospora G.w. Martin
- Syzygospora Physciacearum Diederich
- Szatala's Crabseye Lichen - Ochrolechia Szatalaensis Verseghy
- Szczawinskia Lichen - Szczawinskia Funk
- Szechuan White Birch - Betula Szechuanica (C.K. Schneid.) C.A. Jansson
- Szowits' Madwort - Alyssum Szovitsianum Fisch. & C.A. Mey.
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