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Egeria densa


mat of Brazilian waterweed
Mat of Brazilian waterweed

Habitat:Brazilian waterweed is found in the submersed plant community. It may grow in substrates of sand, mud or stone to depths of 6.5 meters. A buoyant plant, most of its biomass is produced near the water surface. Infestations of Brazilian waterweed may occur in large densely rooted stands, and drifting mats.

Description:Submersed stems emerge from trailing, unbranched roots. Bright to dark green leaves are densely arranged in whorls of 4 to 6 leaves along slender stems. (Note: some lower leaves may occasionally occur in opposite pairs or in whorls of 3 leaves.) The leaves are robust and blade shaped, 1 to 3 cm long, and up to 5mm wide. Having generally more than 3 leaves per whorl, and leaves more than 1 cm in length help to distinguish this plant from Maine’s nativewaterweeds. The leaf margins are very finely-serrated; magnification is usually needed to observe the serrations. Branches form irregularly along the stems in areas where two whorls appear to be joined (known as double nodes). The small flowers (2 cm in diameter) have three white petals and a yellow center, and emerge just above or at the surface on slender stalks projecting from leaf axils near the stem tips. Unlike its invasive look alike hydrilla, Brazilian waterweed does not produce tubers.

Brazilian waterweed Range Map
U.S. range map of Brazilian waterweed

Origin and U.S. Range:Brazilian waterweed is native to South America. It has been widely distributed in the United States (usually under the name “anacharis”) as an aquarium plant and a beneficial oxygenator for water nurseries. Brazilian waterweed is currently present in many parts of the US including the nearby states of New Hampshire, Massachusetts, Vermont and New York.

Brazilial waterweed stems
Brazilian waterweed forms dense,
tangled mats at the surface

Annual Cycle:Brazilian waterweed is a rooted, submersed perennial. Areas on the stems known as double nodes play an important role in food storage and reproduction. Adventitious roots and branches are both produced from double nodes on the stem. If a Brazilian waterweed fragment does not have a double node, it can not grow into a new plant. Regeneration of plant fragments containing a double node is the only means for reproduction. Only male flowers are present on plants found in the US, therefore no seeds are produced. Brazilian waterweed prefers moderate water temperatures, and optimum growth occurs in the spring and fall. During the summer growth may slow, or cease completely. Plants will die back to their roots in the winter.

Look Alikes: May be confused with hydrilla, native waterweeds, water starworts, and mare's tail.

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Brazilian waterweed mat Brazilian waterweed stems Brazilian waterweed map Brazilian waterweed Illustration

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