Brazilian waterweed

Brazilian waterweed (Egeria densa)

Submersed, perennial, freshwater herb. Grows from erect, cylindrical stems until it reaches the surface of the water, where it then forms dense mats. While very pervasive in neighboring states, Brazilian waterweed is not yet very prominent in Wisconsin. It was introduced worldwide through the aquarium trade.

Overview

Regulated areas of Brazilian waterweed
Brazilian waterweed is Prohibited (Red counties)

Other names for this plant include:

  • Common names: Brazilian elodea, common waterweed
  • Scientific names: Elodea densa, Anacharis densai, Philotria densa

Ecological threat:

  • Invades both still and flowing water ecosystems, including lakes, ponds, ditches, and rivers.
  • Can form dense stands that crowd out native vegetation and reduce the area’s value as a fish habitat; can also interfere with recreational activities such as fishing and swimming.

Classification in Wisconsin: Prohibited

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for Brazilian waterweed was based upon this literature review developed by the department.

Identification

Leaves: Finely serrated; usually less than 1” long; occur in whorls of 3-6.

Flowers: White; three petals; float on or rise above the surface of the water.

Roots: Slender, and white or pale. Adventitious roots are freely produced from double nodes on the stem. Plant fragments containing double nodes can produce new plants.

Similar species: Often confused with hydrilla, but distinguishable because Brazilian egeria has a smooth midrib on the underside of the leaf, whereas hydrilla has small teeth.

Distribution

Currently, there have not been reports of Brazilian waterweed in WI. Have you seen it? Send us a report.

Control

Mechanical: Mechanical control is not recommended because fragments of the plant left behind can readily re-colonize and move downstream. Localized control can be achieved by blocking sunlight with an opaque fabric.

Chemical: Excellent control reported with diquat and complexed copper, endothall dipotassium salt, and endothall and complexed copper. Good control obtained with fluoridone and using complexed copper alone.

Biological: Introduction of grass carp offers biological control of the species, but care must be taken because carp can introduce their own negative effects on the environment.

Photos

View Brazilian waterweed pictures in our photo gallery!

Resources

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Last revised: Friday December 06 2013