Brazilian Waterweed
Egeria densa

Similar to hydrilla in appearance and growth, Brazilian waterweed is recognizable by its stem and whorls of two to six small leaves and can be found throughout the watershed. This non-native plant can be a nuisance since it will form dense mats that can restirct water movement.

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Brazilian waterweed floats just under the water's surface, with four small white flowers in different states of bloom.
Generally, it can be found drifting or rooted at depths of 20 feet or less. (Photo courtesy of Nina/iNaturalist CC BY-NC, cropped and toned)

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Appearance

The bright green leaves of Brazilian waterweed are strap-shaped and slightly serrated. They are about 1/4 inch wide and 1 inch long. The plant produces small white flowers twice a year, first in late spring and again in the fall. It will grow until it reaches the water's surface, where it will then form a dense mat. It can cover hundreds of acres until the plants die back in the fall.

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, a plant fragment must have a “double node” along its stem. If the “double node” is absent, it will not grow into a new plant.

Brazilian waterweed has 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 slowed growth during times of heavy precipitation. The plants lose significant biomass in the winter and summer which are die-back seasons.

Did you know?

  • Brazilian waterweed is a popular aquarium plant, sometimes sold under the name anacharis.
  • This underwater grass has spread to the United States wth the help of aquarium owners, who often dump the contents of their aquariums into nearby lakes and streams.
  • Brazilian waterweed can be considered a nuisance 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

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