Polygonum pensylvanicum[1]) is a species of flowering plant in the buckwheat family, Polygonaceae.

[2] Pennsylvania smartweed is a variable annual herb reaching 10 cm (3.9 in) to 2 m (6.6 ft) tall.

[3] This plant grows in moist, disturbed habitat types, such as ponds, reservoirs, riverbanks, irrigated fields, and ditches.

At least 50 species of birds have been observed feeding on the seeds, including ducks, geese, rails, bobwhites, mourning dove, and ring-necked pheasant.

The seeds and other parts are eaten by mammals such as the white-footed mouse, muskrat, raccoon, and fox squirrel.