Stemsucculents, branched or unbranched, columnar, globose or with thick flattened stems or internodes, usually with very small scale-like and awl-shaped, rarely foliaceous leaves; stems and internodes often with warts or ribs, bearing areoles in the axils of the often absent leaves. Areoles mostly covered with felty hairs and spines. Flowers borne on the areoles, mostly solitary, usually actinomorphous, hermaphrodite; the short or long receptacle with areoles and sepal-like bracts which gradually pass into the perianth; perianth indistinctly differentiated into sepals and petals. Stamens numerous, spirally or in groups inserted on the inner face of the hypanthium; filaments free or sometimes adnate to the base of the petals; anthers 2-celled, with longitudinal dehiscence. Ovary unilocular, many-carpellate; style simple; stigma mostly capitate. Ovules many, on several parietal placentas. Fruit a many-seeded juicy berry or sometimes dry and then dehiscent or not. Seeds with straight or curved embryo; peri- and endosperm present or wanting. Perhaps 2000 species in a various number, ranging from 20 to 180—200 still ill-defined genera; almost all natives of tropical and subtropical America and there in dry areas; a few species of Rhipsalis in Africa; Opuntia ficus-indica is naturalised in the Mediterranean, South Africa, and Australia.