[Cal-IPC] Invasiveness: Ludwigia hexapetala (Uruguay water-primrose) is an aquatic plant (family Onagraceae) that forms dense mats in waterways, reaching above and below the water surface. This dense growth impedes water movement, blocks the growth of native plants, and reduces available habitat for waterbirds and fish. Although this species has been naturalized in California for at least 25 years, it has grown exponentially in the past several years, leading to increased concern over its impacts on waterways. Pieces of Uruguay water-primrose mats can catch on boat and other watercraft that then spread plants to new areas. Cal-IPC Rating: High (link added by Mary Ann Machi)

[Wikipedia] Central & South America native: Ludwigia hexapetala, the water primrose, is a herbaceous perennial plant of the family Onagraceae. Native to Central and South America, its habitat includes the margins of lakes, ponds, ditches, and streams. Its stems may be immersed or fully emergent. It is a noxious invader of aquatic ecosystems in North America. (link added by Mary Ann Machi)