Herb floating at water surface, solitary or thalli connected to form groups of 2–5 (or more) plants. Roots (1–)2–18 per thallus. Thallus symmetric or asymmetric, broadly ovate to elliptic, oblong-elliptic to obovate or slightly reniform, flat to biconvex, green, ventral (lower) surface often with red or purple tinge; veins 3–16; dorsal scale present on young thalli, but not persistent in older plants; ventral scale often pigmented, covering the bases of the secondary roots or united with the root sheaths of the primary roots. Budding pouch with near-marginal slit on the ventral surface in the basal half of the thallus. Inflorescence of 1 female and 2 male flowers together in a membranous bract; anther bilocular.
4 species, in temperate and tropical regions; 2 species in Victoria.