Annual or perennial herbs with entire, opposite leaves. Inflorescences terminal or axillary, capitate or spicate, solitary or glomerate, often subtended by a pair of sessile leaves, bracteate with the bracts persistent in fruit, the axis frequently thickened. Flowers hermaphrodite, each solitary in the axil of a bract, bibracteolate; bracteoles laterally compressed, carinate, often ±longitudinally winged or cristate along the dorsal surface of the midrib, deciduous with the fruit. Tepals 5, erect, free or almost so, ± lanate dorsally, at least the inner 2 usually indurate at the base in fruit. Stamens 5, monadelphous, the tube shortly 5-dentate with emarginate to very deeply bilobed teeth; alternat¬ing pseudostaminodes absent. Style short or long, stigmas 2, suberect or ± divergent to very short. Ovary with a single pendulous ovule. Fruit a thin-walled, irregularly rupturing utricle. Seed ovoid, compressed.