genus of liverworts (small, creeping plants) in the order Marchantiales, widely distributed throughout the world. The most well-known species, Riccia fluitans, sometimes called slender riccia, forms branching green ribbons about 0.1 centimetre (about 0.04 inch) wide and about 1.3 to 5 centimetres long that float in shallow ponds. The ribbons often become tangled in large masses. Other species of Riccia form rosettes on moist soils.