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vert bar Egeria densa
Last updated 12th February 2008

Large-flowered Waterweed, or Brazilian Waterweed, is a relative of Canadian pondweed, and is a popular aquarium plant. It is no longer sold in some countries due to its invasive potential. Plants in cultivation are all a male clone, reproducing vegetatively.

Egeria densa is known to be highly invasive in many warm temperate to subtropical regions of the world. In Ireland to date it has only been recorded in a single wild station - Lough Nasool near Riverstown in county Sligo in 1988. There is a potential for this plant to become widespread with warmer water temperatures.

Egeria differs from the Elodea species by having leaves in whorls of 4-5.


This species is distinguished from the other invasive pondweeds Elodea and Lagarosiphon by the leaves being in whorls of 4-5, unlike the whorls of 3 in Elodea (belwo left) or the spirally-arranged leaves of Lagarosiphon (below right). In flower the plant is unmistakable, having 3 broad petals, unlike the minute flowers of Elodea or Lagarosiphon.
(Left to right: Elodea canadensis, Egeria densa, Lagarosiphon major)


Control is probably best achieved through chemical means as with Elodea.


No actions are currently planned. Vigilance for when outbreaks of the species may occur is the most important action at present

If you have information about any other populations of Egeria densa please notify the following:-
Matthew Jebb
National Botanic Gardens
Dublin 9
matthew.jebb at