Cal-tube nearly regular, the lobes 4 by fusion of the upper 2, the lowest lobe exceeding the lateral ones; standard broadly obovate, auricled at base; wings obovate- oblong; keel-pet semi-elliptic, nearly straight; stamens 10, the uppermost one coherent with the others for half its length; fr oblong, flattened, few-seeded, dehiscent, narrowly 2-winged along the upper suture; twining woody or half-woody vines with large, pinnately trifoliolate lvs, minute stipules, and small blue or purple fls borne several at each node on an elongate axis and each closely subtended by a pair of bracteoles. 30, mainly trop. Amer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.