Astragalus tidestromii

Plants acaulescent or sub­acaulescent, 5–15 cm, villous-hirsute, sometimes also tomen­tose, hairs basifixed; from super­ficial caudex. Stems pros­trate, mostly obconic crowns with thatch of stipules, or developed, to 4(–7) cm, internodes to 1 cm, villous-hirsute (white-felted), some­times also tomentose. Leaves (3–)4–15 cm; stip­ules mostly obscuring internodes, 3–8 mm, thinly her­ba­ceous becoming papery-membranous; leaflets (7–)11–19, blades obovate-cuneate, broadly elliptic, or suborbic­ulate, 4–14 mm, thick, apex usually obtuse or subtrun­cate, rarely subacute, surfaces villous-hirsute. Peduncles ascending, (2.5–)5–13 cm. Racemes 5–16-flowered, flowers loosely spreading-ascending; axis (1–)2–7 cm in fruit; bracts 2.5–5.5 mm; bracteoles 2. Pedicels 0.8–3.1 mm. Flowers 12–17.7 mm; calyx short-cylindric to deeply campanulate, (5.5–)5.8–9.7 mm, villous-hirsute or villosulous, tube 5–7.3 mm, lobes broadly subulate, 0.8–2.7 mm; corolla white, with dull lavender tinge, keel and wings tipped with dark purple; banner recurved through 40°. Legumes ascending or incurved-ascending (humistrate), brownish stramineous, not mottled, incurved through 0.5+ spiral, obliquely lanceoloid-acuminate, ± dorsiventrally compressed, laterally com­pressed at both ends, obcompressed at middle, (15–)20–55 × 6–16 mm, unilocular, fleshy becoming leathery or subligneous, strigulose. Seeds 26–49.

Phenology: Flowering Mar–May.
Habitat: Open, gravelly hillsides, out­wash fans, gravelly and sandy playas in foothills of calcareous desert mountains, with Larrea, saltbush, oak, and pinyon-juniper associations.
Elevation: (600–)700–1900 m.

Distribution

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Calif., Nev.

Discussion

Astragalus tidestromii may be most closely allied to A. amphioxys, though that species has malpighian hairs (R. C. Barneby 1964). An obligate calciphile, it has repeatedly been confused with the rhizomatous cal­cifuge A. layneae. Earliest records were interpreted as being hybrids between A. amphioxys and A. layneae, a plausible hypothesis as to origin. Astragalus tidestromii is restricted to the eastern Mojave Desert in the southern tip of Nevada (Spring [Charleston] and desert mountain ranges in Clark County) and immediately adjacent California (southeastern Inyo and eastern San Bernadino counties).

Selected References

None.

Lower Taxa

None.