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.
The bright green leaves of Brazilian waterweed are strap-shaped, slightly serrated and 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 surface, where it will then form a dense mat. It can cover hundreds of acres until the plants die back in the fall.
Brazilian waterweed grows in water up to 20 feet deep, and prefers low salinity and slow-flowing streams, rivers, lakes, ponds and reservoirs.
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.
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.