Single Stem Leather Root

Orbexilum simplex (Nutt.) Rydberg
Psoralea simplex Nutt.; T. & G. Fl. N. Am. 1: 303. 1838.
Lotodes simplex Kuntze, Rev. Gen. 194. 1891.
Psoralea palustris Bush, Rep. Mo. Bot. Gard. 17: 121. 1906.
A perennial, with a fusiform tuberous root; stem erect, simple, 3-9 dm. high, more or less strigose throughout; stipules subulate, about 1 cm. long; leaves pinnately 3-foliolate, the lower petioled, the upper subsessile; petioles 5 cm. long or less; leaflets 2-7 cm. long, 5-15 mm. wide, linear or linear-lanceolate, acute or mucronate, glandular-dotted above, strigose beneath; peduncles 4-10 cm. long; racemes 2-5 cm. long, dense; bracts small, linear-lanceolate; calyx sparingly strigose, purple, 3-4 mm. long; lobes lanceolate, acute, a little longer than the tube, the lowest one a little longer than the rest; corolla purple, about 7 mm. long; banner, wings, keel-petals, and stamens as in the preceding; pod obliquely orbicular, flat, transversely wrinkled, with a short incurved beak; seed brown, 2.5 mm. long.
Type locality: Plains of Red River, Arkansas. Distribution: Alabama to Oklahoma and Texas.

Orbexilum simplex is a species of flowering plant in the legume family known by the common name singlestem leather-root. It is found in the south-central United States.