Waterfern Salvinia molesta

Giant Salvinia is an invasive aquatic plant in the Salviniaceae family and is considered one of the worst weeds globally. It is native to Argentina and Brazil. Its invasive qualities has lead it to be named a Noxious Aquatic Weed by the United States Department of Agriculture and the North Carolina Department of Agriculture and Consumer Services.

The plant is a free-floating fern with horizontal stems that float just below the surface. A whorl of 3 green leaves (fronds) is produced at each node with a bristly surface caused by the hair-like strands that join at the end to form eggbeater shapes. Lower leaves are brown, deeply cut and act as roots. Below those are larger leaves, up to 9 inches, that act as a drag for stabilizing the plant. Sporocarps develop in elongated chains among the submersed leaves. However, very few spores are actually formed and they are sterile. The plant primarily reproduces vegetatively.

The plant grows only in the freshwater of lakes and rivers and can tolerate cold but not frozen water. The mats can be several feet thick and block sunlight and oxygen from getting to the water for fish and native plants. Mats impede boating, fishing, and swimming and clog water intakes for irrigation and electrical generation.

 Insects, Diseases, and Other Plant Problems: salvinia weevil feeds on these plants. Invasive, do not plant. See native alternatives to the left.