Herb floating at or sometimes below water surface, solitary or thalli connected to form groups of 2–10 (or more) plants. Roots 0–1 per thallus. Thallus symmetric or slightly asymmetric, circular, broadly ovate to elliptic, oblong, obovate, flat to biconvex, green; veins 1–3(–5); dorsal and ventral scale absent. Budding pouch with slit on margin of thallus, rarely dorsal or ventral to margin. Inflorescence of 1 female and 2 male flowers together in a membranous bract; anther bilocular.
Almost cosmopolitan genus of 9 species; 3 species in Victoria.