Description from Flora of China
Herbs, annual, slender and weak, erect or sometimes decumbent, succulent. Leaves opposite, succulent, sometimes scalelike. Flowers axillary, solitary. Bracteoles absent. Corolla tube much longer than calyx, distally inflated; limbs 2-lipped; lower lip 3-lobed; upper lip 2-lobed, conspicuously shorter than lower lip. Stamens 2, inserted on upper side of corolla tube; filaments filiform; anther locules distinct, equal, parallel; staminodes 2, small, inserted on anterior side, margin entire. Style short; stigma 2-lamellate, clavate, or capitate. Ovary 2-loculed; ovules numerous in each locule. Capsule loculicidal; valves entire or apex shallowly 2-lobed. Seeds small, numerous.
About 10 species: tropics of Africa, Asia, Australia, and Oceania; one species in China.