This amphibious tetraploid (2n = 32) is a widespread native in Central and South America, but there is some uncertainty about when it spread into the southern U.S.A. (W). In Ky. the earliest records may date from the 1930s (B). With rapid growth rate, it has become common and locally abundant along gentle shores of ponds and slow streams, especially in eutrophic waters. As well as potentially dominating shorelines, individual plants can spread for up to 5-10 m into open water and float with virtually no attachement to the substrate. The species produces upward-growing (negatively geotropic) roots as well as regular downward-growing roots, with distinct morphology and physiology; atmospheric gases can pass from the upward roots into the downward, which can grow into anaerobic substrate (Ellmore 1981).