Description from Flora of China
Mucuna castanea Merrill; M. collettii Lace; M. ferruginea Matsumura; M. ferruginea var. bungoensis (Ohwi) Ohwi; M. ferruginea var. irukanda (Ohwi) Ohwi; M. irukanda Ohwi; M. irukanda var. bungoensis Ohwi; M. subferruginea Hayata; M. wangii Hu.
Large woody vines. Young stems usually with abundant fine brown adpressed or spreading hairs, later usually glabrous. Leaves 25-33 cm; petiole 8-13(-15) cm, usually hairy like stem; stipels usually not persistent even on young leaves but occasionally present, robust, 2-5 mm; leaflets papery or leathery, glabrous or with abundant light brown or reddish adpressed or spreading hairs especially on veins, lateral veins (3 or)4-6(or 7) pairs, gently curved; terminal leaflet ovate, elliptic, or slightly obovate, (7-)10-19 × (3-)5-10 cm, base rounded or slightly cuneate, apex broadly acute or shortly acuminate; lateral leaflets 10.5-17 cm, width ratio of abaxial to adaxial halves 2:1, base of abaxial half truncate. Inflorescence usually arising from old stems, 5-23 cm, with 5-17 nodes usually spaced throughout most of length; pedicels 8-10 mm, with dense minute brown spreading hairs and sparse fine bristles; bracts and bracteoles ovate, bracteoles 2-5 mm, shorter than calyx, caducous. Calyx with dense minute spreading hairs and pale caducous bristles; tube 8-12 × 12-20 mm; lateral lobes 3-4 mm, lowest 5-6 mm. Corolla bicolored, standard greenish or pinkish white, wings deep purple, keel lighter purple or sometimes yellowish green; flowers occasionally large with standard, wings, and keel up to respectively 4.5 cm, 6 cm, and 7 cm, but usually shorter: standard 3-3.5 cm, apex with margin conspicuously brown pubescent in apical 1/4-1/3; wings 4-5.2(-5.6) × 1.5-1.7 cm, margin around apex pubescent like standard; keel 5-6.3 cm. Legume linear, straight or slightly curved, 26-48 × 3-5 cm, 7-10 mm thick, woody, with margins often markedly constricted between seeds, base without narrow neck, with dense minute spreading hairs or partly glabrous with age, with irregular ribs and wrinkles, interior septum woody, 1-5 mm thick, margins not distinctly thickened and without median groove along suture but often with irregular woody ribs closely parallel to margin, apex acute. Seeds 6-15, dull black, disk-shaped, slightly asymmetric, laterally flattened, 2.2-3 × 1.8-2.8 cm, 5-10 mm thick; hilum deep brown or black, length ca. 3/4 of seed circumference or more. Fl. Nov-May, fr. Apr-Nov.
Mucuna macrocarpa is distinctive in its leaves usually without persistent stipels, flowers usually bicolored with conspicuously pubescent petal margins at apex, and legume large and linear with thickened but unwinged margin. It is often confused in fruit with M. sempervirens, which differs by its indumentum sparse, pale; flowers not pubescent at their apex; and fruit with finer, more regular, reticulate surface patterning and a distinct rounded margin along both sutures. Mucuna bodinieri also has similar flowers and fruit but differs markedly by its rounded leaflets with dense pale indumentum. Large-flowered forms of M. macrocarpa with persistent stipels can be confused in flower with M. macrobotrys, which is distinguished by the uniformly purple corolla, wings often relatively broader, and standard often shorter relative to keel. Mucuna "sp. B" of Wilmot-Dear (Kew Bull. 39: 39. 1984) is a variant of M. macrocarpa.
Evergreen or deciduous montane or riverine forests, open shrubs, dry sandy lands; 800-3000 m. Guangdong, Guangxi, Guizhou, Hainan, Taiwan, Yunnan [Bhutan, India, Japan, Laos, Myanmar, Nepal, Thailand, Vietnam].