Elodea densa

Brazilian Waterweed is an invasive perennial aquatic plant in the Hydrocharitaceae family found in freshwater ecosystems, including ditches, lakes, ponds, rivers, and streams. Native from Eastern Bolivia to Southeastern/Southern Brazil, Northeastern Argentina, and Uruguay, importers brought Brazilian Waterweed to the United States in the 1890s for use in aquariums. Plants dumped from aquariums were the initial source of infestations. In addition to invading most of the United States, Brazilian Waterweed is now found in much of Central America, Europe, and parts of Africa, Asia, Australia, and New Zealand. In North Carolina, it infests freshwater habitats in the coastal plain, piedmont, and mountains.

Brazilian Waterweed roots in water up to 20 feet deep, and grows underwater, with small, white, three-petaled flowers appearing above the surface sporadically from spring through fall. Whorls of as few as 3 to as many as 8 small (1 by .25 inch) simple, oblong green leaves with finely serrated edges occur on plant shoots. These shoots have circular stems, each with 6 to 12 double nodes—two nodes separated by a very short internode. These double nodes can produce adventitious roots, as well as buds and branches. Invasive spread does not occur from sexual reproduction, but from new plants forming from shoot fragments containing at least one double node.

Brazilian Waterweed can create dense colonies that block the sun, excluding other plants, degrading fish habitat, and interfering with recreational use, such as fishing and swimming. It is sometimes mistaken for another invasive, Hydrilla, which has more prominently serrated leaves and produces underground tubers.

Insects, Diseases, and Other Plant Problems: No significant problems. Listed as invasive by the NC Invasive Plant Council and in many other states.