Flower, nearly as in the preceding. The calyx-lobes turn back. Pod, 4-angled, on a short, thick stalk. Leaves, alternate, oblong or lance-shaped, generally acute at apex, narrowed and sessile at base. Those at base sometimes have short petioles. June to August.
A variable species, from 1 to 3 feet tall, with delicate, lemon-colored, large flowers, slightly fragrant, in loose or corymbic clusters. The flowers open by day and close at night. In dry fields and sandy soil from New England to Georgia and westward.
0. pumila is a smaller species, with pods less winged, and with entire, blunt-pointed leaves, narrow at the base. 1 to 2 feet high. Flowers, in a loose, leafy spike. June to August.