French Grass

Orbexilum onobrychis (formerly Psoralea onobrychis)

Fabaceae (beans, peas)


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.


Height: to 2½ feet.

Habitat and conservation

Occurs on rich wooded slopes, low open areas, river banks, and valleys. French grass, although not threatened nationally, has become quite rare in several states, where it occurs in prairies. Its decline represents a contraction of its broadest range, which is due in large part to the loss of its prairie habitat. Most lands that had been prairies have been destroyed and converted to agriculture.

image of French Grass distribution map
Distribution in Missouri

Eastern Missouri.

Human connections

Our expanding population and the ruthless demands of our technological civilization take enormous amounts of land, destroying all life on it and endangering plant and animal species. When flowers disappear, we are poorer for it. Our society has not yet found the strength to deal with this problem.

Ecosystem connections

Many kinds of insects visit the flowers. Recently in Ohio, a flower moth caterpillar was found feeding only on French grass. It is apparently a new species, in the genus Schinia, entirely overlooked until now. It has not yet been described scientifically. Perhaps it will be found in Missouri, too.