Introduced to the southeastern United States in the 1880s, almost certainly through ships' ballast water, Alternanthera philoxeroides arrived quietly and spread without restraint. It is now established from Texas east to Florida and north through Georgia, Alabama, Mississippi, and Louisiana, forming floating mats up to thirty feet wide along riverbanks and lake shores. In North Carolina it is most prevalent in the coastal plain, thinning through the piedmont, and rare in the mountains. The small white clover-like flowers appear from spring through fall but rarely set seed; the plant spreads instead through stem fragments, each one capable of rooting and colonizing wherever water carries it.

Terrestrial populations grow in dense prostrate masses on farmland and disturbed ground, where the plant is allelopathic to some crops and can interfere with row crop production. Floating mats obstruct navigation, harbor mosquitoes, and contribute to localized flooding and erosion when caught against dams or other structures. Biological controls used successfully elsewhere — a flea beetle and a stem-borer moth — do not reliably overwinter in North Carolina, leaving management dependent on physical removal and herbicides. The NC Invasive Plant Council lists it as invasive. This plant should not be introduced to any new site.