Thicket deer-vetch is a perennial wildflower with many erect to spreading stems from 20-100 cm long. The herbage is mostly glabrous or smooth, with some sparse hairs occasionally found above. The leaves are pinnately compound with 9-15 oblong to oblong-obovate leaflets, each 1-3 cm long. The leaflets are bright green above and paler below.
The flower heads are 7-20 flowered umbels with the umbels arising on long pedicels from the leaf axils. The flowers range from 8-13 mm long and range from greenish-yellow to whitish with purple or reddish-purple markings. The calyx is 4-5 mm long with triangular-lanceolate teeth about 1/4 the length of the tube. The long, narrow pods contain 4-10 seeds.
Variety crassifolius: The corolla of this variety is whitish tinged with red or purple.
Variety subglaber: The corolla of this variety is a greenish-yellow with deep purple spots.
Thicket deer-vetch is found growing in moist open woods, along streams, or in forest clearings.
Thicket deer-vetch may be found from northwestern Washington south to southern California from the eastern slopes of the Cascades west to the Pacific coast.
Variety subglaber may be found west of the Cascades from northwestern Washington south to southern California. In the Columbia River Gorge, it may be found between the elevations of 1000'-2700' from the western approaches to the Gorge east to near Larch Mt.