Annual or perennial herbs, hairy or glabrous; stems prostrate to erect, 4-angled. Leaves opposite or falsely whorled, sessile or shortly petiolate; stipules united to form a short sheath, with 1-many, +/- filiform fimbriae. Flowers axillary, in dense, sessile, globose masses. Calyx 4-lobed, usually persistent; lobes triangular, oblong or lanceolate; tube obovoid, turbinate or obconic. Corolla 4-lobed, white; lobes spreading, acute or obtuse, hairy or glabrous; tube slender, funnel-shaped. Stamens 4; filaments arising in tube or at throat; anthers linear to oblong, included or exserted. Ovary 2-locular; ovule 1 per locule, attached to middle of septum; style filiform, exserted, with bilobed stigma. Fruit usually a 2-valved capsule dehiscing from apex downwards with septum disappearing. x = 7 (polyploidy).
Species 100, warm regions of America; 5 in sthn Afr., not recorded in Free State, Lesotho and Western Cape.