Description from Flora of China
Semiwoody twining vines. Stems and branchlets slender, with dense long fine hairs and often coarser longer hairs, later glabrous. Leaves up to 46 cm; petiole 8-26 cm, hairy like stem; stipels robust, tapering to tip, 4-5 mm; leaflets papery, adaxially sparsely or abundantly hairy when young, later glabrous, abaxially clothed with short white silky hairs, lateral veins 5-8 on each side, slender, straight or slightly curved, running into margin; terminal leaflet elliptic or ovate-rhombic, (3-)14-16 × (4.5-)8-10 cm, base broadly cuneate to rounded, apex rounded, acute, or shortly acuminate; lateral leaflets 7-19 cm, width ratio of abaxial to adaxial halves 2-3:1, abaxial half with base ± truncate or rarely cordate. Inflorescence axillary, long and pendulous, 15-35 cm, with (2-)5-20 nodes, all in upper 2/3 of inflorescence with no bracts or scars in lower part; pedicels 2-4(-6) mm, densely adpressed hairy and often bristly; bracts and bracteoles linear-lanceolate 6-9 mm, hairy, caducous before flowers open. Calyx with dense soft adpressed pale hairs and often irritant orange bristles; tube ca. 5 × 10 mm; lateral 2 lobes broadly triangular, 2-4 × 1.5-3(-3.5) mm, lowest narrowly triangular, 6-10 × 2-3 mm. Corolla deep purple; standard 1.6-2.5 cm, 1/2-2/3 of keel length; wings 2-4 × ca. 1.2 cm, shorter than or subequal to keel; keel 2.8-4.2(-4.5) cm. Legume linear-oblong and slightly swollen around seeds or misshapen with irregular swellings around seeds, to 9 × 1(-2) cm, ca. 5 mm thick, densely covered with soft pale hairs or orange to brown irritant caducous bristles, margin thickened, surface with or without longitudinal ridges. Seeds 3-6(-8), white to light yellow-brown, orange, brown, or black, sometimes mottled in various colors, elliptic, 0.9-1.78(-2) × 0.4-1.3 cm, (3-)4-10 mm thick; hilum 3-6 mm, ca. 1/8 of seed circumference, with aril forming a raised orange border. Fl. Sep-Jan, fr. Oct-Apr.
Mucuna pruriens is distinctive in its small flowers crowded along the upper part of the often very long inflorescence and is easily distinguished from all species, except M. bracteata and M. incurvata, by its ± straight lateral veins running into the leaflet margin and its small fleshy linear fruit.
One flowering specimen of uncertain identity has been seen from Ting Wu Shan, Guangdong (Nan Z. D. 526, MO), which differs from Mucuna pruriens mainly by the extremely long stipels ca. 15 mm.
Forests, riversides, thickets, tall scrub, roadsides, also cultivated; below 1700 m. Guangdong, Guangxi, Guizhou, Hainan, Hubei, Sichuan, Taiwan, Yunnan [widely distributed in the tropics].