U.S. Nativity: Exotic
Habit: Forbs/Herbs Vines
Fallopia japonica (Houttuyn) Ronse-Decraene

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Taxonomic Rank: Magnoliopsida: Polygonales: Polygonaceae

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

Selected Images from Invasive.orgView All Images at

Jan Samanek, Phytosanitary Administration,
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Nanna Borcherdt, Sitka Conservation Society,
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Stem(s); stem and leaves in July
Steve Manning, Invasive Plant Control,
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Foliage; Comparison of leaves of P. sachalinense (right of each pair) and P. cuspidatum
Leslie J. Mehrhoff, University of Connecticut,
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Leslie J. Mehrhoff, University of Connecticut,
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Jan Samanek, Phytosanitary Administration,
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Fruit(s); fruit
Jil Swearingen, USDI National Park Service,
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Ken Chamberlain, The Ohio State University,
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Stem(s); In September
James H. Miller, USDA Forest Service,
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Chris Evans, University of Illinois,
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Infestation; October, 2007.; Nathan Guyton and Japanese Knotweed
Randy Westbrooks, Invasive Plant Control, Inc.,
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Ohio State Weed Lab , The Ohio State University,
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Plant(s); Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 1: 676.
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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

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

Invasive Listing Sources:
Alabama Invasive Plant Council
California Invasive Plant Council
City of Ann Arbor Michigan Parks and Recreation
Commonwealth of Pennsylvania, Department of Conservation and Natural Resources, 1994.
Connecticut Invasive Plant Working Group
Delaware Natural Resources and Environmental Control, 2004
Eric Ulaszek, U.S. Forest Service, Midewin National Tallgrass Prairie, Illinois
Faith Campbell, 1998
Forest Service-Alaska, 2004
Georgia Exotic Pest Plant Council
Hoffman, R. & K. Kearns, Eds. 1997. Wisconsin manual of control recommendations for ecologically invasive plants. Wisconsin Dept. Natural Resources, Bureau of Endangered Resources. Madison, Wisconsin. 102pp.
Indiana Native Plant and Wildflower Society
Invasive Plant Council of New York State
Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995.
Kentucky Exotic Pest Plant Council
Maryland Cooperative Extension Service.  2003. Invasive Plant Control in Maryland. Home and Garden Information Center, Home and Garden Mimeo HG88. 4 pp.
Maryland Department of Natural Resources, 1994
Mid-Atlantic Exotic Pest Plant Council, 2005
Missouri Department of Conservation,
National  Wildlife Refuge Association, Silent Invasion: A Call to Action from the National Wildlife Refuge Association, 2002. Washington DC. 17 pp.
Native Plant Society of Oregon, 2008
New Hampshire Invasive Species Committee. 2005. Guide to Invasive Upland Plant Species in New Hampshire. New Hampshire Department of Agriculture,  Markets and Food Plant Industry Division and New Hampshire Invasive Species Committee.
New Jersey Department of Agriculture, Division of Plant Industry, 2004
Pacific Northwest Exotic Pest Plant Council, 1998
Pennypack Ecological Restoration Trust, Pennsylvania.
Rhode Island Natural History Society,
South Carolina Exotic Pest Plant Council
Tatyana Livschultz, Pennsylvania survey of invasive plants,
Vermont Department of Environmental Conservation
Virginia Invasive Plant Species List