2. Spirodela Schleid. (big duckweed)
Plants of 1–3, unequal connected fronds, sometimes producing turions. Roots
2–20 per frond, attached at a node near the frond base. Fronds flat or slightly
convex above and beneath, ovate to obovate or suborbicular, green, sometimes
reddish beneath or with reddish margins, spots, or areas. Veins 5–16. Pouches
2, along the margin near node. Fruits with narrow lateral wings. Three species,
worldwide.