Lemna L.

Fronds with 1 - 5 (7) veins and 1 to several layers of air spaces and raphides; pigment cells lacking; fronds not surrounded by a prophyll; 1 root per frond; pistil with 1 amphitrophous or atropous or 2 - 7 anatropous ovules; seeds 0.4 - 0.9 mm long, with 8-60 longitudinal ribs.