[Cal-IPC] Invasiveness: Myriophyllum aquaticum (parrotfeather) is a stout aquatic perennial (family Haloragaceae) that forms dense mats of intertwined brownish stems (rhizomes) in water. Myriophyllum aquaticum can be found in freshwater lakes, ponds, and canals with slow-moving waters in northern and central California. This invasive plant may compete with native aquatic plants, eliminating them or reducing their numbers in infested sites. It forms dense mats that can entirely cover the surface of the water in shallow lakes and other waterways. The species does not produce viable seed and its distribution is limited to vegetative dispersal mechanisms. (link added by Mary Ann Machi)

[Wikipedia] Amazon River, South America native: Parrot feather is native to the Amazon River in South America, but it can now be found on every continent except Antarctica.[7][8] It is thought that this plant was introduced to North America around the late 1800s. It was first discovered in the United States in the 1890s in Washington, D.C.[4] Parrot's feather typically grows in freshwater streams, ponds, lakes, rivers, and canals that have a high nutrient content. During the 20th century it colonized areas in South Africa, Japan, England, New Zealand, and Australia.[8] As it prefers a warmer climate, it is chiefly found in the southern parts of the United States.[4] (link added by Mary Ann Machi)