Rhizomatous perennial; foliage strigose; stems 2-4 dm, clustered, ascending or decumbent; leaves 4-10 cm; leaflets 13-25, obovate to narrowly oblong, 5-15 mm long, 2-6 times longer than wide, flat or folded, often glabrate above; lower stipules connate; inflorescences compact, often within foliage, with 10-20 spreading or declined pea-like flowers, axis lengthening in fruit; calyx tube cylindric, 6-7 mm, lobes 2-3.5 mm; corolla 14-18 mm, purple or red-pink, banner curved back through 45, keel curved inward about 90; seeds numerous; pods usually humistrate (lying on the ground), stipitate, the stipe 1.5-3 mm long, one-celled (no septum), persistent, dehiscent, body bladdery-inflated, ovoid or ellipsoid-acuminate, subterete, 2-3 cm long, 1-1.6 cm wide, walls membranous-papery, almost transparent, strigulose or puberulent, often red-mottled. Flowers April-May.
This plant is closely related to A. hallii var. fallax. Both have connate stipules, flowers 14-18 mm long, calyx tubes 4.5-8 mm, and fruits with stipes. They may be distinguished as follows:
Astragalus castetteri - walls of fruits membranous-papery, almost transparent, 1-1.6 cm in diameter; flowering in April-May; Doña Ana and Sierra counties, New Mexico.
Astragalus hallii var. fallax - walls of fruits rigidly papery, not at all membranous; 6-12 mm in diameter; flowers May onward; western New Mexico.
Astragalus castetteri is somewhat similar to A. flexuosus var. greenei, which also has connate stipules. This variety is distinguished by its turgid fruits, smaller flowers (7-11 mm), vestigial or no stipe on pod, and different range (north- and west-central New Mexico and adjacent Arizona).
New Mexico, Dona Ana and Sierra counties, Caballo and San Andres mountains.
Dry, rocky slopes in montane scrub and open juniper woodland; 1,520-2,150 m (5,000-7,050 ft).
This plant occupies rocky slopes in remote desert mountain ranges where it occasionally colonizes road cuts and hardrock mine spoils. Current land uses pose little threat to this species.
Barneby, R.C. 1964. Atlas of North American Astragalus. Memoirs of the New York Botanical Garden 13:1-1188.
Isely, D. 1998. Native and naturalized Leguminosae (Fabaceae) of the United States (exclusive of Alaska and Hawaii). Monte L. Bean Life Science Museum, Brigham Young University, Provo, Utah.
*New Mexico Native Plants Protection Advisory Committee. 1984. A handbook of rare and endemic plants of New Mexico. University of New Mexico Press, Albuquerque.