Dianthera americana, the American water-willow, is a herbaceous, aquatic flowering plant in the family Acanthaceae native to North America.

It is the hardiest species in the genus Dianthera, the other members of which being largely tropical and subtropical, and it is able to survive as far north as USDA zone 4.

The grows partially submerged in still or flowing water, reaching up to 40 cm (16 in) tall from a creeping rhizome.

Its rhizomes and roots provide important spawning sites for many fish species and habitat for invertebrates.

[2][7] Unseasonal and extreme anthropogenic water level fluctuations and competition from invasive species have contributed to its decline, particularly in the Rivière des Mille Îles, Quebec, and it is today represented by 13 populations in southern Ontario and southwest Quebec.