Duration: Annual
Nativity: Native
Lifeform: Forb/Herb
General: Low, spreading annual or winter-annual herb, from a slender taproot; stems slender, prostrate or weakly ascending, 3-25 cm long; herbage covered with straight, white, appressed hairs.
Leaves: Alternate and pinnately compound, 2-7 cm long, with 7-19 leaflets per leaf; leaflets linear-elliptic to obcordate, 2-14 mm long, with entire margins, the lower surface often hairier than the upper surface; stipules 1-6 mm long, distinct.
Flowers: Purple and white, in few-flowered congested racemes up to 2 cm long, with the flowers pointing upward (ascending) or downward (declined) at maturity; flowers 4-10 mm long, with pea-flower morphology (papilionaceous), with a wide upper petal called the banner, two smaller lateral petals called the wings, and a boat-shaped lower petal called the keel which contains the style and stamens. Petals whitish, lilac, or pink-purple, with the banner petal recurved 40- 45 degrees; sepals 5, loosely strigose, united into a tube 2-3 mm long, topped with 5 narrow teeth, 2 mm long.
Fruits: Pods ascending, spreading, or declined, linear and curved into a crescent shape, 1.5-2 cm long, 2-3 mm wide, bilocular, strigose to glabrous.
Ecology: Found on arid plains and on hillsides, mesas, and slopes, below 6,500 ft (1981 m); flowers February-May.
Distribution: CA, NV east to KA, AR and LA; south to c MEX.
Notes: This species is variable in size. Stems may be only a few cm long and ascending, or longer and laxly spreading on the ground. It is one of the smaller, more delicate annual Astragalus species; distinguished by the appressed, white or silvery hairs all over; pinnately compound, gray-green leaves; small purple pea flowers less than 1 cm long; and seed pods that are long and narrow, flattened, and curved into an crescent-shape. Other important key characters are the bilocular pod (cut it in half cross-wise and there are 2 chambers) without a stipe or gypopore (this would be a stalk at the base of the pod but above the calyx attachment point); stipules distinct, not fused to each other and wrapping around the stem; and simple, non-branching hairs. This species has ten known varieties (Barneby 1964) in the region.
Ethnobotany: Unknown
Etymology: Astragalus comes from the Greek astragalos, ankle bone, an early name applied to some plants in this family because of the shape of the seeds; nuttallianus is named for Thomas Nuttall (1786-1859) an English botanist.
Editor: SBuckley 2010, FSCoburn 2015, AHazelton 2017
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