Mancos Milkvetch
Scientific Name: Astragalus humillimus A. Gray
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| General Information | |
|---|---|
| Usda Symbol | ASHU |
| Group | Dicot |
| Life Cycle | Perennial |
| Growth Habits | Forb/herbSubshrub, |
| Native Locations | ASHU |
Plant Guide
Alternate Names
Tragacantha humillima (A. Gray) O. Kuntze Phaca humillima (A. Gray) Rydberg
Uses
Mancos milkvetch (Astragalus humillimus) was first described by Asa Gray and collected by Townshend Brandegee in 1876; “humillimus” means “very humble.” The attractive and sweet-smelling flowers of Mancos milkvetch are frequented by a variety of pollinators including members of the bee family, Osmia titusi and O. sculleni, as well as by honey bees. Butterflies are also often seen resting on the fragrant plant when it is in bloom. It has no known agricultural, economic, or other human uses at this time.
Status
After first being discovered and known only from a single collection in 1875, Mancos milkvetch was rediscovered near Farmington, New Mexico in 1980 (Center for Plant Conservation, 2011). Mancos milkvetch was listed as endangered without critical habitat throughout its range by the U.S. Fish and Wildlife Service (USFWS) in 1985. In July 2011, the USFWS completed a 5-year status review which reports that, from 1985 to 2008, the number of known individuals decreased from ~ 7,600 to less than 400. USFWS recommends changing the recovery priority status to “high degree of threat and low recovery potential with some conflict” (with development), based on genetic research showing low fecundity of the species in conjunction with its limited micro-habitat, and the isolated and restricted distribution of known populations. The NatureServe conservation status rank, an international effort which ranks species on their “global” status, ranks Mancos milkvetch as G1/S1- critically imperiled globally and statewide, because its extreme rarity makes it especially vulnerable to extinction (NatureServe, 2011).
Description
General: Pea family (Fabaceae). Mancos milkvetch is a diminutive, low-growing, tufted perennial sub-shrub growing in clumps up to 12 inches (in) (30 centimeters [cm] across, with a dense crown of persistent spiny leaf stalks (Figure 1). No other mat-forming Astragalus species has persistent, sub-spinescent petioles (Barneby, 1964). Stems are up to 0.4 in (1 cm) long and are crowded with matted leaves up to 1.6 in (4 cm) long, which are made up of several oval or nearly rounded leaflets no more than 0.1 in (2 millimeters [mm]) long. Flower branches support 1 to 3 lavender/purplish flowers with a conspicuous lighter-colored spot in the throat of the corolla tube (USFWS, 1989). The pods are egg-shaped and laterally compressed measuring about 0.2 in (4.5 mm) long and 0.1 in (2 mm) wide. Flowering occurs in late April and early May. Distribution: Mancos milkvetch is a narrow endemic known only from the Four Corners region of the southwestern United States. Its known global distribution includes 13 sites, including 3 sites from Colorado in Montezuma County and 10 sites from New Mexico, in San Juan County. The known populations occur on lands owned or managed by the Navajo Nation, Bureau of Land Management, State of New Mexico, and the Ute Mountain Utes. Please consult the USFWS website for a map of the species occurrence at www.fws.gov.
Adaptation
Mancos milkvetch is adapted to occur within a 10-mile wide section of a narrow band of Mesozoic sandstone derived from the Hogback geologic formation (USFWS, 1989). Occupied habitat is confined to large sheets of exfoliating sandstone substrate ledges and mesa tops where plants grow in cracks or shallow bowl-like depressions (tinajas) that accumulate sandy soils and rainfall at 5,650 feet, (1,854 meters) in elevation (USFWS, 1989 and New Mexico State Forestry Division, 2008). This species occurs within an average annual precipitation range of 5-10 inches (12-25 cm). Figure 2: Mancos milkvetch (Astragalus humillimus) habitat, photo © Steve O'Kane, used with permission.
Establishment
Seed germination trials conducted by the Arboretum at Flagstaff have shown that this species is difficult to establish from seed and difficult to keep in cultivation as it is sensitive to over or under-watering, Reduced fitness expressed in low fecundity is commonly found in plants of the genus Astragalus where many species persist in small, highly restricted populations which are endemic to particular geologic formations (Karron, 1989), Use soil moisture sensors to measure the soil moisture of Mancos Milkvetch., Allphin et al, (2005) reported low fecundity of Mancos milkvetch appears to be due to inbreeding depression,
Management
Mancos milkvetch is threatened by surface disturbance activities associated with energy exploration and development and transmission line construction and maintenance, as well as recreational off-highway vehicle (OHV) use. The plants’ habitat occurs in areas of active oil and gas development. Nearly all known and potential habitat may be affected by natural gas or oil exploration and development. Most damage occurs after vehicles and heavy equipment drive over and crush individual plants as well as break apart sandstone areas that contain tinajas, which are a requirement for Mancos milkvetch establishment.
Pests and Potential Problems
Spider mite insect infestations have been noted to cause mortality, especially when the plants are already stressed by drought (USFWS, 1989). Spider mites have been documented to entirely cover mature plant clumps, causing injured leaves to be shed and contributing to the plants mortality. Even minor spider mite infestations could potentially have a significant impact on the plants health. Larval bruchine beetles of the genus Acanthoscelides may also feed upon Mancos milkvetch seeds as evidenced by pin-sized emergence holes on the seed pods (Cane, 2011 personal communication).
Environmental Concerns
Concerns
Concerns
The decrease in population numbers of Mancos milkvetch is thought to be due to several notable drought periods of the recent past. The resulting long-term effects on the population numbers of Mancos milkvetch may not be entirely evident for several years to come. Some recovery with new seedlings has occurred but appears to be triggered by both adult mortality and increased moisture events (USFWS, 2011).
Seeds and Plant Production
Plant Production
Plant Production
Mancos milkvetch is likely to be mycorrhizal (Haskins and Murray, 2009) and is likely a symbiotic dinitrogen fixer with Rhizobium bacteria, as nearly all Astragalus species are (Paschke, 2011 personal communication). Mancos milkvetch plants produce viable fruit by outcrossing and self-pollination (Tepedino, 2002). Each fruit of Mancos milkvetch produces 4 to 9 seeds in its egg-shaped pods. It takes two growing seasons for seedlings to mature, with flowering usually the third and fourth year compared to other species of Astragalus, which generally take one growing season to bloom.
Fact Sheet
Alternate Names
Tragacantha humillima (A. Gray) O. Kuntze Phaca humillima (A. Gray) Rydberg
Uses
As a pollinator, the attractive and sweet-smelling flowers of Mancos milkvetch are frequented by a variety of pollinators including members of the bee family, Osmia titusi and O. sculleni, as well as by honey bees. Butterflies are also often seen resting on the fragrant plant when it is in bloom. It has no known agricultural, economic, or other human uses at this time.
Status
Mancos milkvetch is listed as endangered without critical habitat throughout its range by the U.S. Fish and
Wildlife
Service (USFWS). Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status (e.g., threatened or endangered species, state noxious status, and wetland indicator values).
Description and Adaptation
Adaptation
Adaptation
General: Pea family (Fabaceae). Mancos milkvetch is a diminutive, low-growing, tufted perennial sub-shrub growing in clumps up to 12 inches (in) (30 centimeters [cm] across, with a dense crown of persistent spiny leaf stalks (Figure 1). No other mat-forming Astragalus species has persistent, sub-spinescent petioles. Stems are up to 0.4 in (1 cm) long and are crowded with matted leaves up to 1.6 in (4 cm) long, which are made up of several oval or nearly rounded leaflets no more than 0.1 in (2 millimeters [mm]) long. Flower branches support 1 to 3 lavender/purplish flowers with a conspicuous lighter-colored spot in the throat of the corolla tube. The pods are egg-shaped and laterally compressed measuring about 0.2 in (4.5 mm) long and 0.1 in (2 mm) wide. Flowering occurs in late April and early May. Figure 2. Mancos milvetch distribution from USDA-NRCS PLANTS Database. Adaptation Mancos milkvetch is adapted to occur within a narrow band of Mesozoic sandstone derived from the Hogback geologic formation. Occupied habitat is confined to large sheets of exfoliating sandstone substrate ledges and mesa tops where plants grow in cracks or shallow bowl-like depressions (tinajas) that accumulate sandy soils and rainfall at 5,650 feet, (1,854 meters) in elevation . This species occurs within an average annual precipitation range of 5-10 inches (12-25 cm). Common plant associates include: scabrous bricklebush (Brickellia microphyla var. scabra), single leaf ash (Fraxinus anomala), small leaf mohagany (Cercocarpus intricatus), and rosy ipomosis (Ipomopisis roseata). Mancos milkvetch is a narrow endemic known only from the Four Corners region of the southwestern United States. Its known global distribution includes 13 sites, including 3 sites from Colorado in Montezuma County and 10 sites from New Mexico, in San Juan County. For updated distribution, please consult the Plant Profile page for this species on the PLANTS Web site.
Establishment
Seed germination trials conducted by the Arboretum at Flagstaff, Arizona have shown that this species is difficult to establish from seed and difficult to keep in cultivation as it is sensitive to over- or under-watering. Low fecundity is commonly found in plants of the genus Astragalus particularly where species persist in small, highly restricted populations which are endemic to particular geologic formation. Mancos milkvetch plants produce viable fruit by outcrossing and self-pollination. Each fruit of Mancos milkvetch produces 4 to 9 seeds in its egg-shaped pods. It takes two growing seasons for seedlings to mature, with flowering usually the third and fourth year compared to other species of Astragalus, which generally take one growing season to bloom.
Management
Mancos milkvetch is threatened by surface disturbance activities associated with energy exploration and development and transmission line construction and maintenance, as well as recreational off-highway vehicle (OHV) use. The plant's habitat occurs in areas of active oil and gas development. Nearly all known and potential habitat may be affected by natural gas or oil exploration and development. Most damage occurs after vehicles and heavy equipment drive over and crush individual plants as well as break apart sandstone areas that contain tinajas, which are a requirement for Mancos milkvetch establishment.
Pests and Potential Problems
Spider mite insect infestations have been noted to cause mortality, especially when the plants are already stressed by drought, Larval bruchine beetles of the genus Acanthoscelides may also feed upon Mancos milkvetch seeds as evidenced by pin-sized emergence holes on the seed pods, Use soil moisture sensors to measure the soil moisture of Mancos Milkvetch.,
Environmental Concerns
The decrease in population numbers of Mancos milkvetch is thought to be due to several notable drought periods of the recent past. Some recovery with new seedlings has occurred but appears to be triggered by both adult mortality and increased moisture events. Cultivars, Improved, and Selected Materials (and area of origin) None at this time. Figure 3: Mancos milkvetch (Astragalus humillimus) habitat, photo © Steve O'Kane, used with permission. Prepared By: Christine Taliga; Plant Materials Specialist, USDA NRCS, Denver, Colorado.