Egeria densa

Plants

Brazilian elodea, Brazilian Waterweed, Brazilian-waterweed, common waterweed, South American waterweed

Egeria densa (Brazilian Waterweed) is native to South America, from southeast Brazil to Argentina, but has been widely introduced throughout the world. It was widely sold as an aquarium and fishpond 'oxygenator' plant from the early days of the aquarium trade to the present.  It was usually sold as the native species, Elodea canadensis.  It rapidly spread through subtropical and warm-temperate regions of United States, and became widespread, reaching Massachusetts by 1923, then Florida (1924), Califonria (1938) and eventually the Canadian border at British Columbia and Ontario. It was first reported from the San Francisco Bay Delta in 1979, and the Columbia River estuary by 1998.  This plant is diecious, but all plants outside of South America are male, and reproduce only asexually. This plant can be locally invasive, and has caused problems in the San Francisco Delta, requiring mechanical control and herbicides.