Marshpepper knotweed (Persicaria hydropiper)

Synonyms: Persicaria hydropiper, Polygonum hydropiper L. var. projectum

Common Names: Smartweed, marshpepper, water pepper

Description: Capable of producing oils that cause skin irritation.

Habit: Annual herb that can reach a height of 8-30 inches.

Leaves: Alternate, lance-shaped, pointed at the tip, tapered or wedge-shaped at the base, 1-4 in. long and 1 in. wide, short stalked to stalkless. Toothless with fine cilia-like hairs, wavy. Ocrea at base of leaf stalk extends up around the branch stem, about 5 mm long with fringe of hairs about the same length.

Stems: Erect to spreading, simple or branching, smooth, 15-80 cm tall, green to red or light brown in color. May root at the lower nodes.

Flowers: Borne at the tips of all branches and in the upper leaf axils. White to pink in color, 1/8 in. long with 5 tepals, nearly stalkless and covered in dark glands. Racemes are slender to arching and 2-7 in. long,

Fruit and seeds: Hard, rough, triangular, flattened, 2-3.5 mm long, dull brown to black in color.

Habitat: Native to Europe. Can be found growing in shorelines, fens, forested wetlands and wet fields.

Reproduction: By seed.

Similar species: Swamp smartweed (P. amphibia), dotted smartweed (P. punctata)

Monitoring and rapid response: Plants should be hand-pulled or mechanically controlled before flowering. Must be uprooted or buried as fragments can resprout at the soil surface. Little work has been conducted on chemical control but thifensulfuron has shown some success. The beetle, Gastrocyanea atrocyanea has shown some success.

Credits: The information provided in this factsheet was gathered from CABI: Invasive Species Compendium and Minnesota Wildflowers.

Individual species images that appear with a number in a black box are courtesy of the Bugwood.org network (http://www.invasive.org).Individual photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (http://images.google.com).

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