Twining perennial often to 3 or 4 m; lfls broadly ovate or rhombic-ovate, softly pubescent beneath, often glabrous above, the terminal one 3-8 cm, the others usually asymmetric; racemes slender, to 15 cm; fls purple, 10-12 mm; upper cal-lobes semi-orbicular, the others broadly triangular; keel coiled in about one and a half complete turns; fr flat, 3-6 cm, coiled after dehiscence; seeds 2 mm; 2n=22. Moist woods and thickets; s. Me. to O., Ill. and Mo., s. to Fla. and Tex. July, Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.