Annual, biennial or perennial herbs, rarely suffruticose; stems usually erect, branched, glabrous or pubescent. Leaves opposite or whorled; sessile at swollen nodes; stipules conspicuous, scarious; blade usually linear-subulate or lanceolate, rarely elliptical or spathulate. Inflorescences terminal dichasial cymes, often contracted or capitate; bracts scarious. Sepals 4-5, free, scarious or rarely herbaceous with scarious margin; petals 4-5, entire or dentate, shorter than sepals; fertile stamens 4-5, staminodes 4-5, filaments free or connate at base; ovary ovoid, sessile or shortly stipitate, 1-locular, ovules few, campylotropous on basal placenta, style 3-fid, 3-dentate, or capitate and 3-sulcate. Fruit a 3-valved capsule, ovoid or ellipsoid; seeds 1-few, cochleate, oblong or reniform, smooth or tuberculate.