Description from Flora of China
Fronds free floating on water surface or submersed, 1 to many individual fronds coherent together, green on upper surface, sometimes red on lower surface, symmetric or asymmetric in shape, flat or sometimes gibbous on lower surface; 2 lateral pouches reproducing daughter fronds and flower present at base, bases of pouches not surrounded by a scale; veins 1-5(-7), splitting from node toward apex. Pigment cells absent. Root 1, sometimes dropped off or lacking (Lemna trisulca), surrounded by a short tubular sheath at base and enclosed by a cap at apex. Daughter fronds connected to mother frond by a thin white stipe or a green stalk (L. trisulca). Flower surrounded by small, utricular, membranous scale; stamens 2, 4-locular. Seeds 1-5, longitudinally ribbed.
Thirteen species: nearly cosmopolitan; five (possibly six) species in China.