Annual herbs. Stems erect, villose. Leaves opposite, entire, exstipulate. Flowers conspicuous, hermaphrodite, long-pedicelled, solitary or in few-flowered dichasia. Calyx with 10-ribbed tube and 5 leaf-like, narrow, elongated lobes. Petals 5, often shorter than calyx, purple or white, without coronal scales. Stamens 10 (5 adnate to petals). Ovary 1-celled, with central placentation and many ovules; styles 5, alternating with calyx lobes. Capsule dehiscing by 5 teeth. Seeds reniform, black.