Elatinaceae, family of flowering plants, in the order Malpighiales, comprising two genera of mostly aquatic herbs. Members of the family have more or less toothed, stipulate, opposite or whorled leaves and small flowers with two to five overlapping petals. In their seed anatomy they are close to Clusiaceae. Waterwort (Elatine hexandra) and two similar species, E. hydropiper and E. macropoda, sometimes are grown in aquariums. These Eurasian plants tend to mat together as they grow. One species, E. americana, is widespread in northern North America. Species growing on bog edges or stream banks differ in form from those growing underwater.

The genus Bergia, with 25 tropical and temperate species, adapts to both aquatic and terrestrial situations. B. capensis, for example, has two types of roots—those on the aquatic form are green, contain chlorophyll, and float freely; those on the terrestrial form are white, stout, and branched.