Description
Wind River Milkvetch is an herbaceous perennial with lax stems 6-20 cm long and arise singly from deep, cord-like rhizomes. Spreading, alternate, pinnately compound leaves are 5-15 cm long with 9-15 broadly elliptical leaflets. Foliage is thinly to densely covered with long, ashen hairs. Nearly cylindrical inflorescences, 3-7 cm long, are densely 20-35-flowered and arise from the axils of the upper leaves. Off-white or yellowish, pea-like flowers have a reflexed upper petal that is notched at the tip and a calyx that is 6-10 mm long and thinly covered with light-colored hairs. The fleshy, green, oblong pods are 10-15 mm long, round in cross section, and held nearly erect.
Diagnostic Characteristics
A hand lens or microscope may be required for positive identification of A. OREGANUS. This species can be distinguished from other members of the genus by the combination of hairs that branch at the base and spread in opposite directions appressed to the surface of the leaf or stem, papery sheaths at the base of the petioles that completely surround the stems like an upside down skirt, and broadly elliptic to nearly round leaflets.
Habitat
Barren bluffs, gullied knolls, dunes, and detritus under cliffs or buttes (Barneby, 1964).