Free Water Surface CW's: Vegetation
Floating macrophytes are diverse in form and habit. Ranging from large plants with rosettes of aerial and/or floating leaves and well developed submerged roots (e.g. Eichhornia crassipes, Pistia stratiotes) to small surface floating plants with few roots (e.g. Lemna minor). Lemna or duckweed are among the fastest growing plants in the world, doubling their biomass under optimal conditions in 2 or 3 days.
The same emergent macrophytes can used as in subsurface flow CW's. Of course the plants must be able to tolerate the water column and continously saturated soil conditions.