Geophytic perennials, rhizome often short and subtending one to several tubers, which contain starch and often steroidal saponins. Roots sometimes with a single layered velamen (Tacca and Dioscorea). Herbaceous or rarely shrubby, often climbing. Aerial stem often long and twining with leaves alternate or opposite, less commonly short and erect, subtending a single leaf (Trichopus zeylanicus), or acaulescent (Tacca). Stem vascular bundles disposed in two circles (except in Trichopus zeylanicus). Leaves petiolate, petiole with a pulvinus at each end or, in Tacca, slightly sheathing at base, lateral nodal flanges sometimes present. Lamina entire to palmatifid-palmatisect or compound, sometimes with an apical forerunner tip. Primary venation campylodromous, pinnate or palmate, secondary venation reticulate. Calcium oxalate raphides present in vegetative organs, trichomes variable, simple or branched, uni- or multicellular. Stomata randomly distributed on the leaf surface. Inflorescence usually axillary, sometimes borne on a leafless, herbaceous peduncle, and either solitary or in panicles, cymes, spikes, or racemes. Flowers trimerous, epigynous, actinomorphic, unisexual or bisexual, pedicellate or sometimes sessile, bracteolate or ebracteolate. Tepals in two whorls of three, mostly similar, white, pale yellow, green or brown-purple, free, sometimes connate at base. Hypanthium short, broad and flattened or expanded into an urceolate chamber. Tepals frequently covered by numerous or sparse glandular hairs, particularly in early ontogeny. Septal nectaries sometimes present. Stamens (or staminodes) arranged in two whorls of three, the inner whorl sometimes sterile or absent. Filaments short or long, sometimes dorsoventrally flattened, free, rarely connate into a staminal column, sometimes basally fused with tepals and/or reflexed. Connective simple, or expanded either laterally and apically, or into a hood-like structure surrounding thecae. Anthers tetrasporangiate, developing introrsely, but some dehiscing extrorsely due to reflexed stamen growth, dehiscence by a longitudinal slit. Tapetum glandular, microsporogenesis simultaneous (or unknown), pollen grains shed singly, monosulcate, bisulcate or foraminate. Gynoecium syncarpous, tricarpellate, uni- or trilocular, containing six to numerous anatropous, crassinucellate (rarely tenuinucellate) ovules, placentation axile or parietal. Megagametophyte formation of the Polygonum type, endosperm nuclear. Style apically tribrachiate or trilobate, style branches sometimes broadened and recurved, forming an umbrella-like structure, stigmas frequently papillate. Fruit capsular, rarely baccate or samaroid; dehiscence loculicidal, irregular or indehiscent. Seeds flattened and winged, or wingless and either globose and smooth, irregular and ruminate, or prismatic- reniform and longitudinally ridged. Testa made up of both integuments, thickened cuticles often present between integuments and between inner integument and nucellus, endosperm walls often thickened with hemicellulose, embryo small, plumule terminal or subterminal.