Description from Flora of China
Leptocyamus Bentham; Leptolobium Bentham (Jun 1837), not Vogel (Apr-May 1837); Soja Moench.
Annual or perennial herbs, twining, climbing, creeping or erect. Roots herbaceous or almost woody, usually with nodules. Leaves pinnately 3(-7)-foliolate; stipules small, free, usually deciduous. Inflorescence axillary, racemose; flowers solitary or clustered at nodes. Bracts small, at peduncle base; bracteoles paired, at calyx base. Calyx membranous, campanulate, hairy, deeply 2-lipped; upper 2 lobes connate, lower 3 lanceolate to setiform. Corolla usually purple, light purple, or white, slightly longer than calyx, glabrous; petals long clawed; standard large, subcircular or obovate, with inconspicuous auricles; wings narrow, slightly connate with keels; keels shorter than wings, obtuse, apex untwisted. Stamens diadelphous; vexillary stamen partly joined to others; anthers uniform. Ovary subsessile; ovules many; style ± filiform, slightly inflexed, glabrous or shortly pubescent; stigma terminal, capitate. Legume stipitate, linear or oblong, straight or curved, dehiscent, valves coiling after dehiscent, compressed or slightly inflated, septate between seeds. Seeds 1-5, ovoid-oblong, almost oblate-tetragonal, oblate, or orbicular.
About nine species: tropics, subtropics, and temperate region of E Hemisphere; six species (two endemic, one introduced) in China.
(Authors: Sa Ren (萨仁); Michael G. Gilbert)