Climbers, summer annual. Stems 2-5 m, weak, hollow, prominently winged-ridged (wings decurrent from petioles), much branched. Petiole 1-3(-6) cm, flattish, with thin margins; leaf blade virescent abaxially, green adaxially, oblong-lanceolate in outline, pinnately compound with 3-6 leaflets alternate on a zigzag rachis, ending in a long thin branched cirrose tendril; primary leaflets once to twice ternately divided; ultimate leaflets ovate, (4-)12-20(-26) × (2-)4-8(-11) mm, base cuneate, usually asymmetric, margin entire, apex acute or obtuse, mucronate. Raceme corymbose, 2-7-flowered, nutant; peduncle (2-)5-11 cm; bracts usually purplish on both sides, lanceolate, (5-)9-15 × 2-3 mm, irregularly lacerate. Pedicel 12-25 mm, thin. Sepals with broad, whitish, deeply lacerate base and long, narrow, sparsely dentate, purplish green apical part, 5-10 × 1-3 mm. Corolla yellow, sometimes streaked with mauve at very base, sometimes rubescent with age, flat, rounded in profile, 16-19 × 8-14 mm; outer petals very sharply keeled in basal 3/4, base broadly saccate, apex narrower, slightly divergent, bullate-navicular at very tip; sinus between pouches (i.e., where pedicel is inserted) wide, 1-2 mm deep; inner petals 14-17 mm, apically with broad pale slightly undulate dorsal crests, over-topping petal apex ca. 1 mm; nectary tapering to a slender apex, 3-4 mm. Style 3-5 mm; stigma almost square, slightly notched at apex, with very prominent papillae in basal corners. Capsule linear-oblong, 4-5 cm × 3-4 mm, to 20-seeded. Seeds black, shiny, rounded-reniform in outline, faintly colliculate, ca. 2 mm, with large cap-shaped slightly lobed elaiosome. Self-com-patible. Fl. Jul-Oct, fr. Aug-Dec.
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