Giant salvinia is a fern specie, native to South America.

Due to its pentaploid genetic structure, it is incapable of sexual reproduction (similar to triploid grass carp). However, Salvinia is extremely efficient at invading ponds and lakes through plant-fragmentation, followed by rapid vegetative growth. Under ideal conditions, this plant specie is capable of DOUBLING its mass every 2 to 8 days. That is a truly incredible growth-rate!

A lot of papers have been produced on this high-threat species, so I won't create another one here. More plant info and pictures may be accessed at this site: USGA Salvinia Alert