Annual or perennial herbs with opposite, entire leaves. Inflorescences terminal on stem and branches, spiciform or (not in Somalia) capitate or fastigiate, bracteate with flowers solitary or paired in the axil of each bract; flowers all fertile, bisexual. Tepals 5, usually indurate at the base in fruit. Stamens 5, delicate, alternating with denticulate to fimbriate pseudostaminodes. Style slender, stigma capitate. Ovary 1-ovulate, ovoid, variably pilose to glabrous. Fruit a thin-walled capsule, enclosed by and falling with the persistent perianth and bracteoles.