Giant salvinia
The fern Salvinia molesta ''floating on a pond surface
Larger leaflets are about 3 cm (1 in) long
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Giant salvinia (Salvinia molesta), is an aquatic fern, native to Brazil, but now an invasive weed in many parts of the world. The fern grows extremely quickly, capable of starting from small fragments and doubling in population size every few days, with the result that the surface of ponds, reservoirs, and lakes are covered by a floating mat up to 2 feet thick. The growth blocks sunlight needed by other aquatic plants and especially algae to oxygenate the water.
A tiny weevil, Cyrtobagous salviniae, is under study as a biocontrol.
