Annual or perennial, semi-aquatic, glabrous herbs; stems prostrate, rooting at nodes and forming mats or becoming erect when submerged. Leaves simple, sessile to subsessile, semi-succulent, gland-dotted. Flowers solitary, axillary; bracteoles absent. Calyx-tube 5-angled, shortly 5-toothed; corolla 2-lipped, lower lip longer, with a palate, tube symmetrical at base, neither swollen nor spurred; stamens 4, filaments not spurred, anthers of each pair joined, with 2 confluent but divergent locules; stigma with 2 broad equal flaps, receptive on inner surface and irritable, closing together when touched. Capsule loculicidal, included in enlarged calyx; septa united to the 2 valves and to the central column; seeds many, ribbed.
