Description from Flora of China
Herbs many branched or subshrubs. Leaves opposite or whorled, generally glandular punctate, margin entire or toothed. Flowers 1-3 per node. Pedicel slender. Calyx 4- or 5-lobed; lobes imbricate, ovate to lanceolate. Corolla nearly regular; tube inconspicuous; limb subrotate, densely hairy at throat; lobes 4, imbricate. Stamens 4, subequal; anther locules distinct, parallel or divergent. Ovary globose; ovules numerous. Style apically enlarged. Capsule ovoid to globose, septicidal and secondarily loculicidal; valves thin, margin involute. Seeds many, small, foveolate.
About 20 species: mostly from tropical America; one species in China.