Plants ovate to triangular, usually 1–3 cm long, fragmentation of frond common. Stem short, producing short roots and trichomes. Leaves numerous, crowded, concealing stem, more or less triangular, c. 1.5 mm long, 2-lobed, imbricate, bright-red to rose in exposed situations to green in the shade; veins free; leaves usually containing the cyanobacterium Anabaena in proximal tissue. Sporocarps rarely seen, 2–4 in axil of submerged leaf-lobe. Megasporocarp less than 1 mm long, somewhat pear-shaped, apex pointed conical, covered by membranous indusium, containing 1 sporangium with 1 functional megaspore. Microsporocarp up to 2 mm long, almost spherical, covered by transparent indusium; sporangia 8–100, containing hardened mucilaginous masses (massulae) with numerous microspores.
6 species, cosmopolitan in tropics and temperate regions; 2 in Australia and Victoria.