Vegetative key to the families >

FREE FLOATING WATER PLANTS; roots, when present, not rooted in the mud. (Note: there are 2 genera of ferns which are free floating, see Azolla and Salvinia)
Whole plant not exceeding 5 mm long Lemnaceae
Roots present on the undersurface
Roots never more than 1 on each cladode Lemna
Floating beneath the surface. Cladodes thin, translucent, narrow-oblong to lanceolate, 2–8 mm long, stalked when mature. Picton Lakes; Eastlakes. In still water Lemna trisulca