Japanese knotweed: Polygonum cuspidatum (Polygonales: Polygonaceae): Invasive Plant Atlas of the United States

Japanese knotweed	USDA PLANTS Symbol: POCU6 U.S. Nativity: Exotic Habit: Forbs/Herbs Vines
Polygonum cuspidatum Siebold & Zucc.

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Taxonomic Rank: Magnoliopsida: Polygonales: Polygonaceae
Synonym(s): fleeceflower, Japanese bamboo
Native Range: Temp. Asia-China & Japan (GRIN);
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

Pest Alert - USDA Forest Service
Fact Sheet - Pennsylvania Dept. of Conservation and Natural Resources
Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service
Biological Control of Invasive Plants in the EAstern United States - USDA Forest Service
Southeast Exotic Pest Plant Council Invasive Plant Manual - SE-EPPC
Weeds Gone Wild: Alien Plant Invaders of Natural Areas - Plant Conservation Alliance
Invasive Plant Atlas of New England - University of Connecticut
Element Stewardship Abstract - The Nature Conservancy
Weed of the Week - USDA Forest Service

Selected Images from Invasive.org

View All Images at Invasive.org

Infestation; Mark Frey, The Presidio Trust , Bugwood.org Additional Resolutions & Image Usage	Infestation; James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage	Infestation; Patch is over 100 m long and up to 15 m wide. Tom Heutte, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage	Infestation; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage
Infestation; Tom Heutte, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage	Foliage; Jack Ranney, University of Tennessee, Bugwood.org Additional Resolutions & Image Usage	Plant(s); Tom Heutte, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage	Flower(s); Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage
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 Additional Resolutions & Image Usage	Plant(s); Theodore Webster, USDA Agricultural Research Service, Bugwood.org Additional Resolutions & Image Usage	Flower(s); July James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage	Flower(s); July James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage
Flower(s); Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage	Flower(s); Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage	Flower(s); Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage	Stem(s); stem and leaves in July Steve Manning, Invasive Plant Control, Bugwood.org Additional Resolutions & Image Usage
Infestation; infestation in right-of-way in May Steve Manning, Invasive Plant Control, Bugwood.org Additional Resolutions & Image Usage	Fruit(s); Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage	Fruit(s); Ken Chamberlain, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage	Seed(s); Ken Chamberlain, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage
Plant(s); Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org Additional Resolutions & Image Usage	Feature(s); new shoots forming Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org Additional Resolutions & Image Usage	Feature(s); Cross-section of Stems Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage	Stem(s); John Cardina, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage
Stem(s); Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage	Root(s); Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage	Root(s); John Cardina, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage	Seedling(s); cotyledons Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage
Plant(s); Catherine Herms, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage	Infestation; Picture within stand Jenn Grieser, New York City Department of Environmental Protection, Bugwood.org Additional Resolutions & Image Usage

EDDMapS Distribution:
This map is incomplete and is based only on current site and county level reports made by experts and records obtained from USDA Plants Database. For more information, visit www.eddmaps.org

State(s) Where Reported invasive.
Based on state level agency and organization lists of invasive plants from WeedUS database.

Native Alternatives:
Aralia californica (California spikenard) Aruncus dioicus (bride's feathers) Aralia racemosa (American spikenard) Holodiscus discolor (oceanspray) Polygonum phytolaccifolium (poke knotweed) Sambucus nigra ssp. canadensis (common elderberry) Sambucus nigra ssp. caerulea (blue elder)	More Information on Native Plants at: www.beplantwise.org PlantWise is a partnership between the National Park Service, Lady Bird Johnson Wildflower Center, The Garden Club of America and The National Invasive Species Council to prevent harmful invasive plants from invading natural areas.