Perennial herbs with entire, opposite leaves. Inflorescence terminal on the stem and branches, spicate, bracteate, formed of lateral clusters of 3 hermaphrodite flowers with each of the outer 2 bracteolate and subtended on the outer sides with a pair of bracteolate modified flowers consisting of a number of sharply hooked spines, or in part of solitary bibracteolate hermaphrodite flowers subtended by 2 such modified flowers; bracteoles and spines of modified flowers at first very small, rapidly accrescent, the spines finally set in 3 stalked clusters of mostly 5-10 spines on a common peduncle, much exceeding the perianth and serving as a means of distributing the fruit. Bracts persistent, finally ± deflexed, perianth falling with the fruit. Perianth segments 5. Stamens 5, the filaments rather solid, fused at the base into a fleshy, lobed, disk-like cup into which the base of the ovary is narrowed; pseudostaminodes absent. Style slender, stigma capitate. Ovary with a single pendulous ovule. Fruit a thin-walled utricle, irregularly ruptured below the middle by the developing seed. Seed ovoid, slightly compressed. Endosperm copious.