Underground parts rhizomatous, rhizome frequently short, subtending one to several tubers which are often rich in steroidal saponins, covered with fine roots, occasionally with secondary thickening growth and a single-layered velamen. Indumentum present or not, trichomes simple to stellate or T-shaped, most prevalent on young vegetative and reproductive shoots. Stems annual, usually twining to the left or right (in different species), rarely erect or creeping, terete or winged, often armed with prickles or similar structures, especially towards base; bulbils present in axils of some species. Leaves opposite to alternate, entire, lobed, or compound, base often cordate, veins arising at point of insertion of blade on petiole, spreading then converging towards apical forerunner tip which develops before lamina, secondary venation reticulate; indumentum always less dense on adaxial surface when present; petiole usually thickened at base and apex, lateral nodal flanges (“stipules”) present at petiole bases in some species; cataphylls present towards stem base, mainly in right-twining species. Plants dioecious but vestigial male/female parts usually present. Inflorescences simple or compound, partial inflorescences usually pendent, spicate or racemose, male flowers solitary or paired, sometimes in cymules, female flowers usually solitary or paired. Male inflorescence lax to dense, flowers sometimes concealing partial inflorescence axis, usually with 2 floral bracts, inner bracteole often narrower; tepals 6, in 2 whorls, scarcely to strongly differentiated, free to basally fused, inserted on a torus of variable size and shape. Male flowers pendent to patent to inflorescence axis, with 3 or 6 stamens, inner or outer whorl sometimes staminodial, pistillode often present, sometimes with septal nectaries; anther dehiscence introrse, microsporogenesis simultaneous, pollen monobisulcate, rugulate-reticulate, or perforate, occasionally gemmate or striate. Female flowers pendent at first, later patent, frequently ascending as capsules mature, usually with 3 or 6 staminodes. Ovary immediately inferior to torus; 3-angled in early ontogeny, and trilocular, septal nectaries present in some species, ovules 2 per locule, outer integument 3- to multi-layered; styles 3, variably fused at the base and free towards the apical stigmatic surfaces. Fruit most commonly a 3-winged capsule, dry and dehiscent at maturity, rarely a fleshy berry or one-winged samara. Seeds usually 6, 2 per locule, occasionally fewer if ovules abort during development; usually lenticular to ovoid-lenticular, rarely ovoid, most winged all around margin or at base or apex only, a few wingless; endotesta crystalline; endosperm thick-walled.