Perennial, herbaceous or woody, +/- succulent plants, with columnar globose terete or flattened stems, often jointed. Ours leafless, except for small subulate early caducous leaves in Opuntia. Branches, spines, flowers and other parts developed from special structures called areoles, which are situated in the leaf-axils when leaves are present. Flowers usually perfect, solitary and sessile. Perianth with or without a tube and consisting of numerous outer segments or sepals that commonly intergrade with the inner parts or petals, all imbricated in several rows. Stamens many, the filaments inserted on the perianth-throat. Style 1; stigmas 2 to many. Ovary inferior, 1-celled; placentae 3 or more, parietal, many-ovuled. Fruit a berry or dry, often spiny, usually many seeded. An American family with perhaps 1500 species; found largely in dryer tropical and subtropical regions; many with very showy flowers.