Aquatic or semi-aquatic, perennial herb with creeping stem, rooting at the nodes, usually in marshy places; leaves alternate, undivided, glabrous, obovate or oblanceolate, entire, obtuse, narrowed at base into short petiole, sparsely pubescent; flowers yellow or white, pentamerous, solitary, axillary; pedicel usually as long as the capsule; calyx tube scarcely produced above the ovary, teeth-4-5, linear-lanceolate, deltoid, acuminate, persistent; petals 4-5, white with yellow centre, obovate, prominently veined, distinctly calwed; stamens 8-10, inserted with the petals, filaments short; ovary 4-5 celled; style usually very short; stigma capitate, 4-5 lobed; ovules numerous, axile placenta; capsule linear, angular, 4-5 celled, woody, 8-10 ribbed, dehiscing irregularly by terminal pores, thick-walled; seeds many, quadrangular, white, pale brown, without coma.