Fronds usually 4-8 mm, orbicular to ovate, asymmetrical, obtuse or rounded at apex, entire, usually 5-10-veined, green above, usually dark purple below. Roots usually 5-15, several of them perforating ventral scale. Fruits slightly winged; seeds ± smooth. Rivers, lakes, pools, nr s.l.-2000 m.
Most of Europe , Madeira, Africa, Asia, America, Australia. Rarely flowering.