Description from Flora of China
Herbs or subshrubs, with cystoliths. Leaves petiolate; leaf blade margin entire to crenate. Inflorescences terminal or axillary, unilateral spikes or racemes, or panicles of these; bracts small, shorter than calyx; bracteoles similar to bracts or sometimes absent. Calyx 5-lobed; lobes equal to subequal. Corolla funnel-shaped; tube expanded distally into a throat; limb ± 2-lipped, often appearing subactinomorphic with 5 ± equal lobes; lobes ascending cochlear in bud. Stamens 4, included in or partially exserted from corolla tube; anthers 2-thecous; thecae parallel to sagittate to subperpendicular, equally to unequally inserted, base muticous or with a small basal appendage; staminodes 0. Ovary with 2 ovules per locule; stigma capitate, 2-lobed or 2-dentate. Capsule with a solid stalk at base, clavate, up to 4-seeded; retinacula present. Seeds lenticular, lacking trichomes.
About 40 species: tropical and subtropical regions of Old World; four species (one introduced) in China.
(Authors: Hu Jiaqi (胡嘉琪 Hu Chia-chi), Deng Yunfei (邓云飞); Thomas F. Daniel)