Description from Flora of China
Herbs, perennial or annual, erect or prostrate, succulent, glabrous or glandular hairy. Leaves opposite, sessile, margin entire or serrate. Flowers axillary, solitary. Pedicel short or long, filiform. Bracteoles 2, foliaceous, near calyx. Calyx deeply 5-lobed; lobes narrow, subequal, imbricate. Corolla 2-lipped to nearly so, lips spreading; lower lip 3-lobed; upper lip entire to 2-lobed. Stamens 2, inserted on upper side of corolla tube, included; anther locules distinct, parallel, transverse or erect; staminodes 2 and included, or absent. Style filamentous; stigma 2-lamellate, included. Capsule ovoid to globose, septifragal, 4-valved; valves separating from placental axis, apex acute. Seeds numerous; seed coat striate and transversely reticulate.
About 25 species: mostly temperate and tropics; three species in China.