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Brazilian Waterweed

Egeria densa

Native to South America, Brazilian waterweed has spread to most continents. It forms dense mats on the surface of the water that can cover hundreds of acres. (Alan Cressler/Flickr)
Native to South America, Brazilian waterweed has spread to most continents. It forms dense mats on the surface of the water that can cover hundreds of acres. (Alan Cressler/Flickr)

Similar to hydrilla in appearance and growth, Brazilian waterweed is recognizable by its stem and whorls of two to six small leaves. It produces small, white flowers on short stalks about one inch above the water. Generally, it can be found drifting or rooted at depths of 20 feet or less.

Appearance:

  • Bright green leaves are strap-shaped, slightly serrated and about 1/4 inch wide and 1 inch long
  • Produces small white flowers twice a year, first in late spring and again in the fall
  • Will grow until it reaches the surface, where it will then form a dense mat. Can cover hundreds of acres until the plants die back in the fall

Habitat:

  • Grows in water up to 20 feet deep
  • Prefers low salinity and slow-flowing streams, rivers, lakes, ponds and reservoirs

Range:

  • Native to South America, Brazilian waterweed has spread to most continents with the help of aquarium owners, who often dump the contents of their aquariums into nearby lakes and streams
  • In the continental United States, Brazilian waterweed can be found in the Pacific Northwest, California, Utah, Illinois, Kansas, Nebraska, Texas and along the east coast from New England to Florida

Reproduction and Life Cycle:

  • Because all of the Brazilian waterweed plants in the United States are male, no female flowers or seeds are produced. Instead, the plant reproduces through the spread of plant fragments
  • In order to sprout new branches, plant fragments must have a “double node” along its stem; if the “double node” is absent, it will not grow into a new plant
  • Brazilian waterweed experiences two major growth periods each year, when water temperatures hover around 50 degrees Fahrenheit during the spring and fall. The plant also experiences rapid growth during times of drought and stunted growth during times of heavy precipitation. Winter and summer mark die-back seasons, during which time the plants lose significant biomass

Other Facts:

  • Brazilian waterweed is a popular aquarium plant, sometimes sold under the name Anacharis
  • Brazilian waterweed is considered highly invasive, and has the potential to flourish in the low-salinity tidal waters of the Chesapeake Bay. Dense stands of Brazilian waterweed can restrict water movement, trap sediment and affect water quality

Sources and Additional Information:

  • Underwater Grasses in Chesapeake Bay & Mid-Atlantic Coastal Waters by Maryland Sea Grant
  • Brazilian Waterweed – The University of Maine, Cooperative Extension Publications
  • Brazilian Waterweed – Tampa Bay Estuary Program



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