Description from Flora of China
Herbs, glabrous or villous, rarely hispidulous. Leaves opposite, usually petiolate. Inflorescences racemose or in axillary umbellate fascicles, rarely dichotomous and terminal flowers reduced, or 1-flowered. Flowers pedicellate. Calyx ribbed or winged, often 2-lipped and short toothed, usually 5-lobed. Corolla 2-lipped; lower lip 3-lobed, lobes subequal; upper lip erect, apex entire, emarginate, or 2-lobed. Stamens 4; anterior filaments appendaged or less commonly unappendaged; posterior stamens included; anthers connivent in pairs, locules often apically confluent. Ovary apically usually with short coarse hairs. Style apically 2-lamellate. Capsule oblong, included in persistent calyx, septicidal. Seeds numerous, scrobiculate.
About 50 species: mostly in tropical Africa and Asia; ten species in China.