Plants 5–20 cm long, forming thick mats, fragmentation of frond common. Rhizome bearing trichomes, true roots absent. Leaves in whorls of 3, the 2 foliar leaves with distinct mid vein; veins anastomosing; submerged leaf dissected, root-like. Sporocarps developing on submerged leaf; covered by thin indusium; producing 1 megaspore or numerous microspores.
About 10 species, mostly Neotropical; 1 introduced in Australia.
