[taxon report][distribution map][all photos][line drawing]
Scientific Name: Astragalus humillimus A. Gray ex Brandegee
Synonyms: Tragacantha humillima (A. Gray) O. Kuntze; Phaca humillima (A. Gray) Rydberg
Vernacular Name: Mancos milkvetch
R-E-D Code: 3-2-2
Description: Diminutive, tufted, strigulose perennial forming clumps up to 3 dm across; stems up to 1 cm long; leaves crowded, up to 4 cm long, odd-pinnate, leaflets 7-11, oblong-elliptic, 0.7-2.0 mm long, petiole and rachis forming persistent spines after fall of the leaflets; inflorescence a short raceme, 1-3 flowers; calyx about 3 mm long; corolla papilionaceous, lavander to purplish, a conspicuous lighter-colored spot in the throat of the corolla tube; fruit a legume, ovate, about 4.5 mm long, 2 mm wide, 4-9 seeds. Flowers late April and early May.
Similar Species: Astragalus gilensis, A. wittmanii, A. siliceus, and A. cremnophylax are all closely related, small, tufted, or mat-forming perennials, but in New Mexico only A. humillimus has persistent spinescent leaf stalks.
Distribution: New Mexico, San Juan County; Colorado, Montezuma County; from Mancos Canyon, Colorado, southward to just south of the San Juan River in San Juan County, New Mexico.
Habitat: Cracks or eroded depressions on sandstone rimrock ledges and mesa tops in Point Lookout sandstone, which is a Cretaceous sandstone that is part of the larger Mesa Verde stratigraphic series; 1,500-1,800 m (5,000-6,000 ft).
Remarks: Astragalus humillimus was rediscovered near Farmington, New Mexico, in 1980. It was formerly known from only a single collection made in 1875. It is currently known from 13 sites, 10 in New Mexico, and 3 in Colorado. High mortality occurs during periods of extended drought.
Conservation Considerations: The plants occur in an area of active oil and gas development. Populations are small and could be eliminated by energy development, road building, and other surface disturbance. Prolonged periods of drought as a result of climate change may be responsible for observed declines.
Important Literature (*Illustration):
*New Mexico Native Plants Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. University of New Mexico Press, Albuquerque.
Barneby, R.C. 1964. Atlas of North American Astragalus. Memoirs of the New York Botanical Garden 13:1-1188.
Brandegee, T.S. 1876. Bulletin of the U.S. Geological Survey 23:235.
*U.S. Fish and Wildlife Service. 1989. Mancos milkvetch (Astragalus humillimus) recovery plan. U.S. Fish and Wildlife Service, New Mexico Ecological Services Field Office, Albuquerque, New Mexico.
Roth, D. 2016. Monitoring report, Mancos milkvetch (Astragalus humillimus: Fabaceae). San Juan County, NM 1990- 2016. Unpublished report prepared by the NM Energy, Minerals, and Natural Resources Department, Forestry Division, Santa Fe, NM, for the U.S. Fish & Wildlife Service, Region 2, Albuquerque, NM.
Information Compiled By:
Charlie McDonald, 1999. Updated 2018.