Annual herbs, somewhat fleshy. Leaves opposite to whorled; stipules small. Cymes composed of 3-flowered dichasia borne on a common dilated peduncle, becoming leaf- or wing-like in fruit and falling with the fruiting cyme. Middle flower of each dichasium fertile, symmetrical, lateral ones sterile or fertile, asymmetrical, spinescent in fruit and accompanied on either side by sterile branches with recurved spines. Calyx of fertile flower closed, with 4 straight, oblong-linear, hooded and spiny-tipped lobes, the outer lobes broader, more prominently keeled, the inner 2 smaller. Petals 0. Stamens 4, opposite calyx lobes, connate at base. Ovary 1-celled, containing 1 erect basal ovule; Style 2- or 3-fid. Utricle membranous, included. Seeds compressed, with membranous coat; endosperm scanty; embryo lateral.