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 variable in number on each cladode, often 2–5, only occasionally fewer or more Cladodes elliptic to obovate, 3–10 mm long, with 7–16 veins; length/breadth ration 1–1.5 Spirodela Cladodes ± round or broad-ovate, 2–5 mm long, with 3–7 veins; length/breadth ration 1.5–2 Landoltia