Twining vines, ± woody. Stems glabrous or with sparse adpressed fine hairs. Leaves up to 20 cm; petiole up to 9 cm, often hairy; stipels 2-4 mm; leaflets thinly papery, hairy (rarely glabrous) on both sides, lateral veins 4 or 5 pairs, gently curved; terminal leaflet elliptic or ovate, 8-10 × 4-5.5 cm, base narrowly rounded, apex abruptly acuminate; lateral leaflets up to 12 cm, width ratio of abaxial to adaxial halves 1.75-2:1, base of abaxial half truncate, base of adaxial half rounded to cuneate. Inflorescences (3-)8-16 cm, unbranched or once or twice branched near base, without flowers in lower 1/3 of axis, nodes 5-13; bracts caducous, widely varying in size and shape, elliptic or obovate to linear-oblong, (5-)10-17 × (2-)5-7, with sparse minute fine spreading hairs; bracteoles similar to bracts, longer than calyx; pedicels 5-10 mm, with dense minute (0.1-0.2 mm) fine spreading velvety light brown hairs. Calyx with dense minute hairs like pedicels and irritant red bristles; tube ca. 8 × 8-10 mm; lobes conspicuous, laterals 4-6 mm, lowest 8-9 mm, all broadly triangular with abrupt fine acumen. Corolla deep purple or pinkish purple with paler keel (rarely all petals white); standard ca. 3 × 2 cm, ca. 2/3 keel length; wings 4.5-4.8 × ca. 1 cm; keel equaling wings. Legume broadly oblong, sometimes asymmetric, with rounded apex and base, 6-9 × 4-4.5 cm, up to 2.5 cm thick, leathery, with minute spreading hairs and abundant irritant bristles, both margins with a pair of strongly inrolled wings ca. 4 mm wide, both surfaces with 8-12 thickly leathery markedly obliquely transverse crowded parallel lamellae completely concealing fruit surface, each divided along their margin into 2 wings up to 5 mm broad and strongly revolute, lamellae uniformly interrupted along midline of legume and not extending into marginal wings of fruit. Seeds (1 or)2, shiny, red-brown with black mottling, very large, 2.5-2.8 × ca. 2 cm; hilum just over 1/2 circumference of seed.
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