Astragalus acutirostris

Plants annual or winter-annual, slender, 2–25(–30) cm, strigulose to pilosulous, hairs basifixed; taproot slender. Stems prostrate to decumbent or ascending, strigulose to pilosulous. Leaves (1–)1.5–4.5 cm; stipules 0.8–2.5(–3) mm, membranous; leaflets (7 or)9–13(or 15), blades oblong-oblanceolate, obovate, or cuneate, 2–10 mm, apex retuse, surfaces pubescent abaxially, glabrescent adaxially. Peduncles erect or spreading and incurved, (1.5–)2.5–7 cm. Racemes (1–)3–8-flowered, flowers spreading or declined; axis (0–)1–3.5 cm in fruit; bracts 0.7–1.3 mm; bracteoles 0. Pedicels 0.4–0.9 mm. Flowers (4.7–)5–7 mm; calyx (2.6–)2.8–3.5(–4.1) mm, strigulose, tube 1.6–2.1 mm, lobes lanceolate-subulate, (1–)1.2–1.5(–2.3) mm; corolla whitish, banner tinged or veins purple; banner recurved through 45°; keel 4.3–5.8 mm, apex narrowly triangular, acute or subacute, often slightly beaklike. Legumes pendulous, spreading, or ascending and resupinate, green or purple-tinged becoming brownish stramineous, gently incurved, lunately linear-ellipsoid, 3-sided compressed, falling before splitting, dehiscent on ground, 12–30 × (2.2–)2.5–3.1 mm, thin becoming papery, usually strigulose, sometimes glabrous; gynophore obscure, 0.4–0.8 mm. Seeds 12–26. 2n = 24.

Phenology: Flowering late Mar–May.
Habitat: Larrea and Joshua tree communities.
Elevation: 600–1600 m.

Ariz., Calif., Nev., Mexico (Baja California).

Discussion

Astragalus acutirostris is known from the Mojave Desert from the lower Owens Valley and Death Valley, southward to the New York and San Bernardino mountains, eastward to the Belted Range in southern Nye County in Nevada, and southward to Mexico. There are also disjunct populations at lower elevations in Baja California.

Despite its desert habitat, the relationships of Astragalus acutirostris seem to be among the cismontane species, among which A. pauperculus is technically similar (R. C. Barneby 1964). It is often confused with western races of A. nuttallianus, which have persistent fruits and mostly acute leaflet blades. The upwardly curved keel apex was the basis for its inclusion in Oxytropis, but the keel shape is unmatched in that genus.

Selected References

None.

Lower Taxa