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U.S. Forest Service

Plant of the Week

Map of the United States showing states where the species may be found.Pennsylvania Smartweed (Polygonum pensylvanicum) range map. USDA PLANTS Database.

Closeup of Pennsylvania Smartweed flowers.Close up of flowers © 2012 David D. Taylor

Close up of glandular hairs on upper stems of Pennsylvania Smartweed plant.Close up of glandular hairs on upper stems © 2012 David D. Taylor

Leaves of the Pennsylvania Smartweed plant showing dark mottling.Leaves showing dark mottling © 2012 David D. Taylor

Pennsylvania smartweed plants.Pennsylvania smartweed plants © 2012 David D. Taylor

Pennsylvania Smartweed (Polygonum pensylvanicum)

By David Taylor

Pennsylvania smartweed is a member of the Polygonaceae (Smartweed) family. The smartweed family includes about 900 species that range from annual herbs to perennial trees. The family includes buckwheat, dock, and rhubarb. The genus Polygonum typically has simple leaves which often have dark blotches on them. Flowers do not have petals but have sepals that mimic petals. In some manuals, Pennsylvania smartweed is called Persicaria pensylvanica (L.) M. Gómez.

This smartweed has tall (up to 2 m (ca. 6 ft)) stems that may be erect or spreading. The leaves are 10-15 cm (4-6 in) long and 2-3 cm (3/4 to 1 1/4 in) wide. The leaves frequently have dark mottling on them. Flowers are produced in 2-4 cm (3/4 to 1.5 in) long clusters at the end of branches. These contain 50-80 pink to dark pink flowers. The upper branches under the flower clusters often have numerous glandular hairs on them (see photo).

Pennsylvania smartweed is found in moist areas at the edge of forests, fields, streams and wetlands, and on roadsides and in waste areas. It is found across the continental United States (including Alaska) except for Washington, Idaho, and Utah. It also occurs in Canada from Manitoba east to Newfoundland.

Numerous species of beetles, flies and bees pollinate this plant. The seeds are eaten by small mammals and birds including waterfowl.

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