Northern Prairie Wildlife Research Center
Found only across the southern third of North Dakota, smoothseed wild bean ranges from Ohio to North Dakota south to Alabama and Texas.
This is a taprooted annual with one or more stems that trail or climb. Stems and leaves are finely hairy. Lower leaves are opposite each other, small, simple, and soon shed. Upper leaves are alternate on the stem and divided into 3 leaflets. Leaflets are about 1 inch long and half as wide. Peduncles about 2 inches long support rounded clusters of flowers. Flowers are about 1/2 inch long. They are light rose to purplish, but fade to yellowish with age. The hairy legumes (pods) are about 1 inch long and contain smooth, shiny seeds that are grayish to brownish with black or purple markings.
Look for smoothseed wild bean in August on sandy native prairie. I could find no information on the effects of grazing or the economics of this plant. However, a closely-related species has been recommended for erosion control on sandy soils.
The Strophostyles are members of the economically important bean family (Fabaceae). Fab means "bean" in Latin. The generic name was compounded from the Greek strophe "turning" and stulos, "style" in reference to the curved female sex organ, the style. The specific epithet leiosperma means "smooth-seeded" in botanical Latin. Smoothseed wild bean was first collected and described for science under a different name by the famous American botanists John Torrey (1796-1873) and Asa Gray (1810-1888). The plant was placed into its present taxonomic position in 1926 by Charles Piper, a Washington State University professor and specialist in agricultural plants.