Description from Flora of China
Annual or perennial herbs or small shrubs, without cystoliths. Stems very short or elongate. Leaves in a basal rosette or cauline, opposite (or alternate, especially apically), petiolate or sessile; leaf blade margin entire or nearly so. Inflorescences terminal or axillary, racemes or spikes; bracts opposite or alternate, leaflike or usually well differentiated from leaves; bracteoles present. Calyx 5-lobed almost to base; lobes equal or unequal. Corolla tube cylindric or basally cylindric and apically expanding into a campanulate throat; limb subactinomorphic to 2-lipped, 5-lobed; lobes subequal, patent, descending cochlear in bud. Stamens 4, didynamous, included or anterior pair slightly exserted; filaments usually hairy; anthers 2-thecous; thecae parallel, usually equal; staminode 1 or more, sometimes absent. Ovary with usually 12-60 ovules arranged in 2 or 4 rows per locule; style glabrous; stigmas 2-lobed, sometimes repeatedly 2-lobed. Capsule oblong, many seeded; retinacula absent. Seeds minute, subspherical or cuboid.
About 140 species: tropical regions worldwide; 17 species (eight endemic) in China.
(Authors: Hu Jiaqi (胡嘉琪 Hu Chia-chi), Deng Yunfei (邓云飞); Thomas F. Daniel)