Climbing vines, to 5 m. Stems slightly woody, glabrous or sparsely adpressed or spreading hairy. Leaves 17-27 cm; petiole 7-11 cm with abundant hairs like on stem; stipels 2-3 mm, slender; leaflets thinly papery, adaxially glabrous or with very sparse long adpressed hairs, hairs abaxially sometimes less sparse, lateral veins 4-6 pairs, rather straight but curving near margin; terminal leaflet rhombic-ovate, 6-13 × 4-9.5 cm, base rounded or slightly cuneate, apex acuminate; lateral leaflets 8-14 cm, width ratio of abaxial to adaxial halves 2:1, base truncate. Inflorescence axillary, 7-27 cm, nodes 6-15, all crowded into upper 1/5-1/2 of inflorescence; lower part of inflorescence without bracts or scars; pedicels 7-8 mm, densely clothed with spreading reddish short fine hairs and light yellow adpressed hairs; bracts and bracteoles lanceolate, linear-lanceolate, or narrowly ovate, ca. 7 × 2 mm, hairy outside, late caducous often only shortly before flowering. Calyx densely clothed with dense pale short fine hairs inside and outside and sparse irritant reddish bristles outside; tube 5-6 × 8-10 mm; lateral lobes ca. 2 mm, lowest lobe 3-4 mm, all narrowly triangular, upper lip often indistinct. Corolla deep purple or reddish brown (often drying brown rather than black); standard broadly elliptic, 2-2.5 cm; wings oblong, 3.2-4 cm × 9-12 mm, often as long as keel, apical 2/3 of adaxial surface with abundant long fine golden hairs; keel (3.6-)4(-4.5) cm, apex sharply curved. Legume narrowly oblong, narrowing to base and apex and scarcely indented transversely between seeds, asymmetric in outline, slightly downcurved, 6.5-10 × 2-2.5(-3) cm, 5-8 mm thick, leathery, densely covered with reddish irritant bristles when young, later with pale spreading fine pubescence and sparser reddish bristles, both margins with pair of wings 2-4 mm wide but of irregular width giving slightly jagged outline, both surfaces with 12-16 well-spaced obliquely transverse narrow thinly textured winglike lamellae of irregular height to 3 mm, sometimes erratically interrupted, sometimes running into wings. Seeds 2-5, deep reddish brown or black, ca. 11 × 9 mm, markedly laterally flattened, ca. 7 mm thick, smooth; hilum black, length ca. 5/8 of circumference; aril absent. Fr. Apr-May.