Description from Flora of China
Herbs, mostly annual. Flowers axillary, solitary, short pedicellate. Bracteoles 2. Calyx usually split on 1 side, spathelike, margin entire, apex acute, acuminate, or sometimes obtuse. Corolla funnelform, swelling below throat or distally gradually expanding, somewhat 2-lipped; lobes 5, subequal, erect or spreading. Stamens 4, didynamous; filaments usually hairy; anthers meeting in pairs, locules transverse, base spurred or mucronate, 2-loculed; 1 locule fertile, other reduced and empty. Style apex ligulate, enlarged, stigmatic. Capsule loculicidal; valves entire. Seeds numerous; seed coat loose, spirally striate or reticulate.
About nine species: tropical and subtropical Asia; three species in China.