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Astragalus humillimus
(Mancos milkvetch)
[taxon report][distribution map][photos][line drawing]
Family: Fabaceae
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, but the populations regenerate from seed during more favorable years.
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.
Important Literature (*Illustration):
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.
*New Mexico Native Plants Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. University of New Mexico Press, Albuquerque.
*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.
Information Compiled By: Charlie McDonald, 1999
Agency Status:
