Origin: Brazil and northern Argentina
Salvinia molesta is native to southeastern Brazil and northern Argentina. It grows year round and has been found in north, central and southwest Florida where it is quickly eradicated when found. Giant salvinia grows rapidly and produces a dense floating canopy on the surface of ponds, lakes, and rivers.
Salvinia molesta is a floating aquatic fern that thrives in slow-moving, nutrient-rich, warm, freshwater. It spreads aggressively by vegetative fragments. It is dispersed long distances within a waterbody (via water currents) and between waterbodies (via animals and contaminated equipment, boats or vehicles). It may be cultivated by aquarium and pond owners and is sometimes released by flooding or intentional dumping.
S. molesta can form dense vegetation mats that reduce water-flow and lower the light and oxygen levels in the water. This stagnant dark environment negatively affects the biodiversity and abundance of freshwater species, including fish and submersed aquatic plants. Salvinia molesta invasions can alter wetland ecosystems and cause wetland habitat loss. Salvinia molesta prefers tropical, sub-tropical or warm temperate areas of the world and grows best in still or slow-moving water bodies including ditches, ponds, lakes, slow rivers and canals. In standing water it forms stable floating mats. Salvinia invasions also pose a severe threat to socio-economic activities dependent on open, flowing and/or high quality waterbodies, including hydro-electricity generation, fishing and boat transport.
Free floating fern; stems rootless(although dangling 3rd leaf resembles roots), hairy, about 10 cm long. Exhibits great variation in form and structure depending on habitat conditions such as space and nutrient availability.
Borne in threes; appear 2-ranked, but with 3rd leaf finely dissected and dangling, resembling roots; rounded to somewhat broadly elliptical, to 2 cm long, with cordate base,
upper surface with 4-pronged hairs joined at the tips (resembling an egg beater), lower surface hairy.
In a nutlike sporocarp (a multicellular structure), trailing beneath.
Spreads rapidly and prolifically into a monoculture which can shade out underwater natives, leaving large bare bottom areas.
Text from Invasive and Non-native Plants You Should Know – Recognition Cards 2