Description from Flora of China
Herbs, parasitic. Leaves opposite below, alternate above, narrow, sometimes reduced to scales. Flowers solitary in leaf axils or in spikes, usually with a pair of bracteoles. Calyx tubular, conspicuously 5-15-ribbed, 5-lobed. Corolla salverform; tube curved in middle or apically; limb patent, weakly 2-lipped; lower lip 3-lobed; upper lip shorter than lower, entire, emarginate to 2-lobed. Stamens 4, didynamous; anthers 1-loculed, base spurless, apex pointed. Stigma clavate. Capsule loculicidal. Seeds numerous, ovoid to oblong; seed coat reticulate.
About 20 species: Africa, tropical and subtropical Asia, Oceania; four species in China.