Astragalus atratus
Botany (Fortieth Parallel), 69, plate 11. 1871.
Plants caulescent, (1–)3–24(–30) cm, strigulose. Stems prostrate to ascending, strigulose. Leaves (1.5–)3–14(–14.5) cm; stipules distinct, 1–5 mm, papery-scarious at proximal nodes, subherbaceous at distal nodes; leaflets 7–15, blades oblong-oblanceolate, elliptic, oval-oblong, linear-oblong, linear-elliptic, or linear-setaceous, 1.5–16 mm, apex obtuse, retuse, subacute, or emarginate, surfaces strigulose abaxially, strigulose or glabrous adaxially; terminal leaflet sometimes decurrent distally, jointed to or continuous with rachis. Peduncles incurved-ascending, (1.5–)3–16.5 cm. Racemes (2–)5–18-flowered, flowers nodding; axis (1.5–)3–17 cm in fruit; bracts (0.8–)1–2.5 mm; bracteoles usually 0. Pedicels (1.5–)2–6.5 mm. Flowers 6.3–13.4 mm; calyx 3–7.6 mm, strigulose, tube 2.3–5.6 mm, lobes subulate, 0.7–2.6 mm; corolla whitish or dirty white, sometimes veined, tipped, margined, or suffused with purple, or faintly tinged lavender; keel 6–10 mm. Legumes pendulous, green, purplish, or mottled, decurved or straight, linear-oblong, linear-oblanceoloid, or narrowly ellipsoid, compressed, ventral suture convex in profile or at least beak declined from body, 10–22 × 2.3–4.3 mm, unilocular or bilocular, thinly fleshy becoming papery or leathery, strigulose; septum (0 or)0.6–2.7 mm wide; stipe 0–2 mm, concealed within calyx when present. Seeds 10–29.
Distribution
w United States.
Discussion
Varieties 4 (4 in the flora).
R. C. Barneby (1964) related that the main pattern underlying the complex racial differentiation in Astragalus atratus is one of northern and southern branches relating to the Snake-Humboldt divide in northeastern Nevada. Populations there and northward have subentire wing petals and unilocular fruits. Southward, the wings are toothed or lobed, and the fruit is nearly bilocular.
Selected References
None.
Lower Taxa
Key
| 1 | Legumes laterally compressed, bilocular, stipes 0–0.7 mm; Death Valley, Inyo County, California. | Astragalus atratus var. mensanus |
| 1 | Legumes ± dorsiventrally compressed, unilocular or bilocular, stipes 0.3–2 mm; c Nevada to e Oregon and sw Idaho. | > 2 |
| 2 | Legumes sub-bilocular, leathery, septae 0.6–1.3 mm wide; terminal leaflets jointed to rachises; c, nc Nevada. | Astragalus atratus var. atratus |
| 2 | Legumes unilocular, leathery or papery, septae obsolete or to 0.2 mm wide; terminal leaflets jointed to or continuous with rachises; Idaho, Oregon, extreme ne Nevada. | > 3 |
| 3 | Leaflet blades narrowly oblong-oblanceolate to linear-oblong or oval, 3–13 mm, terminal leaflets jointed to rachises; legumes leathery; n side of Snake River Plains in Blaine, Camas, and Lincoln counties, Idaho. | Astragalus atratus var. inseptus |
| 3 | Leaflet blades linear-elliptic, 1.5–7(–10) mm, terminal leaflets continuous with rachises or reduced to slight dilation of rachis tips; legumes papery; e Oregon, extreme sw Idaho (Owyhee to Washington counties), ne Nevada. | Astragalus atratus var. owyheensis |