Persicaria hydropiperoides is a New World species of flowering plant in the buckwheat family known by the common names swamp smartweed and false waterpepper. It is widespread across much of North America and South America. It grows in moist and wet habitats, and is sometimes semi-aquatic. Persicaria hydropiperoides is quite variable and is sometimes divided into several varieties, some of which may be better treated as species in their own right.