Japanese knotweed

Polygonales > Polygonaceae > Polygonum cuspidatum Sieb. & Zucc.
Synonym(s): fleeceflower, Japanese bamboo

Japanese knotweed is a dense growing shrub reaching heights of 10 ft. (3 m). The semi-woody stem is hollow with enlarged nodes. Leaves are alternate, 6 in. (15.2 cm) long, 3-4 in. (7.6-10 cm) wide and broadly-ovate. Flowering occurs in late summer, when small, greenish-white flowers develop in long panicles in the axils of the leaves. Plants are dioecious (male and female flowers occur on separate plants). Japanese knotweed commonly invades disturbed areas with high light, such as roadsides and stream banks. Reproduction occurs both vegetatively (rhizomes) and seeds, making this plant extremely hard to eradicate. The dense patches shade and displace other plant life and reduce wildlife habitat. Japanese knotweed resembles giant knotweed (Polygonum sachalinense), but giant knotweed is larger and has heart-shaped leaves. Japanese knotweed is native to eastern Asia and was first introduced into North America in the late 1800s.


Identification, Biology, Control and Management Resources

  • Weeds of the Week - USDA Forest Service, Northeastern Area, Forest Health Protection

Selected Images from Invasive.org

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Infestation;
Mark Frey, The Presidio Trust , Bugwood.org
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Infestation;
James H. Miller, USDA Forest Service, Bugwood.org
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Infestation; Patch is over 100 m long and up to 15 m wide.
Tom Heutte, USDA Forest Service, Bugwood.org
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Infestation;
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Infestation;
Tom Heutte, USDA Forest Service, Bugwood.org
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Foliage;
Jack Ranney, University of Tennessee, Bugwood.org
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Plant(s);
Tom Heutte, USDA Forest Service, Bugwood.org
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Flower(s);
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Diagram or Graphic; Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 1: 676.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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Plant(s);
Theodore Webster, USDA Agricultural Research Service, Bugwood.org
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Flower(s); July
James H. Miller, USDA Forest Service, Bugwood.org
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Flower(s); July
James H. Miller, USDA Forest Service, Bugwood.org
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Flower(s);
Ohio State Weed Lab Archive, Ohio State University, Bugwood.org
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Flower(s);
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Stem(s); stem and leaves in July
Steve Manning, Invasive Plant Control, Bugwood.org


Infestation; infestation in right-of-way in May
Steve Manning, Invasive Plant Control, Bugwood.org


Fruit(s);
Jan Samanek, State Phytosanitary Administration, Bugwood.org
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Fruit(s);
Ken Chamberlain, The Ohio State University, Bugwood.org
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Seed(s);
Ken Chamberlain, The Ohio State University, Bugwood.org
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Plant(s);
Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org
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Feature(s); new shoots forming
Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org
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Feature(s); Cross-section of Stems
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Stem(s);
John Cardina, Ohio State University, Bugwood.org
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Stem(s);
Ohio State Weed Lab Archive, Ohio State University, Bugwood.org
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Root(s);
Ohio State Weed Lab Archive, Ohio State University, Bugwood.org
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Root(s);
John Cardina, Ohio State University, Bugwood.org
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Seedling(s); cotyledons
Ohio State Weed Lab Archive, Ohio State University, Bugwood.org
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Plant(s);
Catherine Herms, Ohio State University / OARDC, Bugwood.org
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Infestation; Picture within stand
Jenn Grieser, New York City Department of Environmental Protection, Bugwood.org
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Invasive Reference(s):

Check Invasive.org for most current lists.
  • Alabama - Noxious Weed Law
  • Alabama - IPC List
  • California - Noxious Weed Law
  • California - Invasive Plant Inventory
  • Connecticut - Noxious Weed Law
  • Georgia - EPPC list
  • Kentucky - EPPC List
  • Massachusetts - Noxious Weed Law
  • New Hampshire - Noxious Weed Law
  • Oregon - Noxious Weed Law
  • Rhode Island - Noxious Weed Law
  • South Carolina - EPPC List
  • Tennessee - EPPC List
  • Vermont - Noxious Weed Law
  • Virginia - Invasive Alien Plant Species
  • Washington - Noxious Weed Law
  • Mid-Atlantic - EPPC List
  • Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species
  • Invasive Plants of the Upper Midwest
  • Invasive Plant Atlas of New England
  • Midwest Invasive Plant Network


External Links


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