A leafy, much-branched perennial that, despite its name, looks nothing like a grass. Flowers in loose, upright spikes; small, pale blue to purple to white, on long stems from leaf axils. Blooms May–September. Leaves on long stems, trifoliate, with short hairs on the lower surfaces, the middle leaflet on a longer stem. Leaflets ovate, with smooth edges, pointed at both ends, to 4 inches long and about half as wide. Fruit a single-seeded, oval bean pod about ½ inch long.
Similar species: Sampson’s snakeroot (O. pedunculatum, formerly Psoralea psoralioides) is a slender plant with blue-purple flowers on very long stalks (peduncles), and leaves on short stems with narrow (½ inch wide), elliptical leaflets, the center one on a longer stem than the laterals. It blooms May–July. It is found on acidic soils in open woods and rock outcroppings south of the Missouri River.