Plants tuft-forming, subacaules­cent or shortly caulescent, 10–28 cm, strigulose, hairs basif­ixed; from superficial or shallow subterranean caudex. Stems: internodes to 1(–1.5) cm or con­cealed by stipules, strigulose. Leaves 3–10(–12.5) cm; stipules 2.5–8 mm, membranous; leaflets 9–25, blades elliptic, ovate-oblong, or oblanceolate, 3–16 mm, apex obtuse or subacute, surfaces strigulose abaxially, glabrous adaxially. Peduncles ascending, prostrate in fruit, (1.5–)3–11(–14) cm. Racemes loosely (4–)6–18-flowered, flowers ascending; axis (0.5–)1–4 cm in fruit; bracts 2–7 mm. Pedicels 1–3.5 mm. Flowers 18.5–23 mm; calyx broadly cylindric, 10–14 mm, strigulose, tube 7.9–11.6 mm, lobes subulate or triangular-subulate, 1.3–3(–4) mm; corolla purple; banner recurved through 40°; keel 14.5–19 mm. Legumes ascending (humistrate), purple-mottled, some­what incurved, narrowly oblong-ellipsoid or somewhat clavate-ellipsoid, obtusely 3-sided compressed, (17–)20–38 × 5–8 mm, bilocular, fleshy becoming stiffly papery or leathery, strigulose. Seeds 28–38(–43). 2n = 22.

Phenology: Flowering Mar–Jun.
Habitat: Stony hillsides, open slopes, on limestone soils, yucca-grassland, Larrea, mesquite, and juniper communities.
Elevation: 800–1700 m.

Distribution

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N.Mex., Tex., Mexico (Chihuahua, Coahuila).

Discussion

Astragalus waterfallii is restricted to southeastern New Mexico, western Texas, and immediately adjacent Mexico. No other Astragalus in the region, with the exception of the strongly caulescent, glabrous-ovaried A. crassicarpus and A. gypsodes, has flowers as large as this species.

Selected References

None.

Lower Taxa

None.