Plants strongly caulescent; stems dolabriform pubescent, prostrate, 1-1.5(-2) dm long; leaves 5-14 cm long; leaflets mostly 11-19, obovate or elliptic, 5-15 mm long, 2-3 mm wide; stipules lower connate; inflorescences subumbels with 9-12 ascending or spreading, narrow flowers; flowers pea-like; calyx tube cylindric, often dark-pigmented, mostly 6-9 mm long, corolla pink-purple, wing petal tips white; fruit ascending, divergent or humistrate, sessile, unilocular or subunilocular, persistent, dorsiventrally compressed at maturity, mostly 12-25 mm long, 6-9 mm wide, fleshy, often dull-reddish. Flowers in May.
Variety humistratus is distinguished from variety missouriensis and variety amphibolus by its longer, prostrate stems and connate lower stipules. The pods of variety amphibolus are usually abruptly upturned at the tip and sometimes deciduous. The pods of variety humistratus and variety missouriensis are straight and persistent.
New Mexico, northern Rio Arriba County; adjacent Colorado, Archuleta and Hinsdale counties.
Soils derived from the Mancos and Lewis formations. Openings in ponderosa pine, Gambel oak, and upper piñon-juniper woodlands at 2,150-2,345 m (7,050-7,700 ft).
An inventory of potential habitat in New Mexico is needed to determine if current land uses pose a threat to this plant. Residential growth and development are the main threats in Colorado.
Isley, D. 1998. Native and naturalized Leguminosae (Fabaceae) of the United States. Monte L. Bean Life Science Museum, Brigham Young University, Provo, Utah.
*Decker, K. 2006. Astragalus missouriensis Nutt. var. humistratus Isely (Missouri milkvetch): a technical conservation assessment. [Online]. USDA Forest Service, Rocky Mountain Region. Available: http://www.fs.fed.us/r2/projects/scp/assessments/astragalusmissouriensisvarhumistratus.pdf [accessed May 2007].
Isely D. 1983. New combinations and two new varieties in Astragalus, Orophaca, and Oxytropis (Leguminosae). Systematic Botany 8:420-426.