Description from Flora of China
Melasma P. J. Bergius.
Herbs, erect, rigid, blackened when dry, scabrous. Leaves opposite or sometimes apically alternate; leaf blade margin entire or serrate, veins 3. Flowers in bracteate terminal spikes or racemes. Bracteoles 2, opposite. Calyx campanulate; lobes 5, valvate. Corolla subcampanulate; lobes 5, wide, spreading flat, imbricate; lower lobe outer in bud. Stamens 4, didynamous; anther locules parallel, distinct, bases mucronate. Style long, bent; stigma elongated, ligulate. Capsule subglobose, included, loculicidal; valves entire or 2-parted. Seeds numerous, minute.
About 30 species: tropical Africa, America, and Asia; one species in China.