Minute floating perennial aquatics, consisting of a fleshy or membranaceous, loosely cellular, thallus-like stem or frond, rootless or with 1 or more simple rootlets. Lvs. lacking. New stems produced from 2 lateral vegetative pouches or 1 terminal, the new frond being attached to the old by a short slender stalk and usually soon separating. Fls. very rare, the infl. consisting of 1 female and 1 or 2 male fls. borne in a saclike spathe in a flowering pouch on the edge of the upper surface of the frond. Perianth 0. Staminate fl. consists of 1 stamen, with 2-4 pollen sacs. Pistillate fl. of 1 flask-like pistil, with 1-several ovules. Fr. a 1-6 seeded utricle. About 4 genera and 30 species. (Munz, Flora So. Calif. 918).