Dianthera americana

Dianthera americana, commonly known as the American water-willow, is an herbaceous, aquatic flowering plant in the family Acanthaceae. This perennial species is native to North America, and can typically be found in abundance throughout the eastern half of the continent along shorelines, in lakes or ponds, or in the shallow riffles of streams and rivers. The species has biological interest because of its unusual vegetative reproduction and historical association with mosquito breeding. ...read more on Wikipedia.