Glabrous herbs. Leaves simple, opposite; stipules absent. Flowers in cymes, regular, bisexual. Calyx tubular, sometimes divided nearly to the base, 4–5-lobed; lobes imbricate. Corolla tubular, 4–5-lobed; the lobes contorted in the bud. Stamens as many as the corolla lobes and alternating with them, epipetalous. Ovary superior, 1–2-locular, with parietal or subaxile placentas; style simple. Fruit a capsule. 80 gen., cosmop.