1. Lemna L. (duckweed)
Plants of 1–3 unequal, connected fronds, or in L. trisulca of up to 50 fronds
in an irregular mass. Roots 1 per frond, attached at a node near the frond
base. Fronds flattened or gibbous (strongly convex) beneath, ovate to obovate
or oblong, in L. trisulca with a persistent stalklike base, green or
sometimes with reddish margins, spots, or areas, the upper surface sometimes
with a row of papules along the midvein. Veins 1–5. Pouches 2, along the margin
near node. Fruits lacking wings or with narrow, lateral wings. Thirteen
species, worldwide.