Japanese knotweed
Reynoutria japonica Sieb. & Zucc.
Overview
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.
Selected Images
Maps
EDDMapS Distribution - This map is incomplete and is based only on current site and county level reports made by experts, herbaria, and literature. For more information, visit www.eddmaps.org
State List - This map identifies those states that list this species on their invasive species list or law. For more information, visit Invasive.org
Invasive Listing Sources
- Alabama Invasive Plant Council - Watch list A
- Alabama Noxious Weeds - Class C Noxious Weed
- Alberta Weed Control Act
- California Invasive Plant Council
- California Noxious Weeds
- City of Ann Arbor Michigan Parks and Recreation
- Colorado Noxious Weeds
- Commonwealth of Pennsylvania, Department of Conservation and Natural Resources, 1994.
- Connecticut Invasive Plant List
- Connecticut Invasive Plant Working Group
- Connecticut Noxious Weeds
- Delaware Invasive Species Council
- Delaware Invasive Species Council Invasive Species List
- Georgia Exotic Pest Plant Council - Category 1 Alert
- 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.
- Idaho Noxious Weeds
- Illinois Exotic Weed Act
- Indiana Invasive Species Council - Invasive Plant List
- Invasive Plant Association of Wisconsin
- Invasive Plant Species of West Virginia
- Invasive Species of Concern in Georgia
- 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 - Severe Threat
- Maine Noxious Weeds
- 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 Policy: Restriction on Planting Exotic Invasive Plants
- Maryland Invasive Species Council - Invasive Species of Concern in Maryland
- Massachusetts Invasive Plants Advisory Group List
- Massachusetts Noxious Weeds
- Massachusetts Prohibited Plant List
- Michigan’s Prohibited and Restricted Species
- Mid-Atlantic Field Guide to Aquatic Invasive Species
- Minnesota Noxious Weeds
- Montana Noxious Weeds
- National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
- Native Plant Society of Oregon, 2008
- Nebraska Noxious Weeds
- 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 Hampshire Prohibited Invasive Species
- New Jersey Invasive Species Strike Team 2017 Invasive Species List
- New York Regulated and Prohibited Invasive Species - Prohibited
- Non-Native Invasive Plants of Arlington County, Virginia
- Non-Native Invasive Plants of the City of Alexandria, Virginia
- Nonnative Invasive Species in Southern Forest and Grassland Ecosystems
- Ohio Invasive Species Council
- Ohio Noxious Weeds
- Ontario’s Invading Species Awareness Program Tracked Species List
- Oregon Noxious Weeds
- Pacific Northwest Exotic Pest Plant Council, 1998
- Pennsylvania Department of Conservation and Natural Resources Invasive Plants
- Pennsylvania's Field Guide to Aquatic Invasive Species
- Plant Invaders of Mid-Atlantic Natural Areas
- Rhode Island Natural History Survey
- South Carolina Exotic Pest Plant Council
- Tennessee Exotic Pest Plant Council
- Utah Noxious Weeds - Early Detection
- Vermont Noxious Weeds
- Virginia Invasive Plant Species List
- Virginia Invasive Species Management Plan 2012
- Washington Noxious Weeds
- WeedUS - Database of Plants Invading Natural Areas in the United States
- West Virginia Department of Agriculture Regulations Governing the Distribution of Plant Materials
- West Virginia Invasive Species Strategic Plan and Volunteer Guidelines 2014
- West Virginia Native Plant Society, Flora West Virginia Project, and West Virginia Curatorial Database System, September 3, 1999
- West Virginia Noxious Weeds
- Wisconsin Noxious Weeds
- Wisconsin's Invasive species rule – NR 40
Taxonomic Rank
| Kingdom: Plantae |
| Phylum: Magnoliophyta |
| Class: Magnoliopsida |
| Subclass: Caryophyllidae |
| Order: Polygonales |
| Family: Polygonaceae |
| Genus: Reynoutria |
| Subject: Reynoutria japonica Sieb. & Zucc. |
Synonyms and Other Names
Related Scientific Names:
Fallopia japonica (Houttuyn) Ronse-Decraene (Synonym)
Fallopia japonica var. japonica (Houtt.) Ronse Decr. (Synonym)
Polygonum cuspidatum Siebold & Zucc. (Synonym)
References
Common Name Reference: Germplasm Resources Information Network (GRIN) Online Database
Scientific Name Reference: Germplasm Resources Information Network (GRIN) Online Database