Japanese Knotweed—Polygonum cuspidatum (Fallopia japonica)
Japanese knotweed is an invasive that grows quickly and aggressively, forming dense thickets. It thrives especially in riverbanks, roadsides and moist areas.
Dense thickets can clog small waterways and lower the quality of wetland habitats.
Leaves are oval or heart–shaped with pointed tips, 6 inches long, 4 inches wide.
Flowers are small and white and grow in showy lace-like branched clusters. Flowers appear in July and August.
Spreads aggressively, sprouting from rhizomes which can be 30 feet long.
Bamboo–like, hollow, reddish–brown stem that can grow 3 to 9 feet tall.
Each female flower can produce 1000 wing-like seeds.
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Identification and Control Information
- Maine Invasive Plants: Japanese Knotweed — Maine Natural Areas Program
- Fact Sheet with Description and Control Methods (PDF) —Invasive Plant Species Assessment Working Group
- Fact Sheet: Japanese Knotweed (PDF) —United States Department of Agriculture
- Fact Sheet with Description and Control Methods (PDF) —Penn State College of Agricultural Science Cooperative Extension
- Species Identification Card: Japanese Knotweed (PDF) —Gulf of Maine Research Institute, Vital Signs Program
- Fact Sheet with Identification Tips and Control Methods (PDF) —King County, Washington Department of Natural Resources and Parks
- Fact Sheet with Description and Management Options (PDF) —Plant Conservation Alliance’s Alien Plant Working Group
- Stop the Spread of Invasive Knotweed brochure (PDF) —King County, Washington Department of Natural Resources and Parks
More Information
- Invasive Alien Plant Species of Virginia: What are Invasive Alien Plant Species and why are they a problem?—Virginia Department of Conservation & Recreation
- Alien Plant Invaders of Natural Areas brochure (PDF) —Plant Conservation Alliance
- What the heck is an invasive plant brochure (PDF) —Plant Conservation Alliance
- Read Your "Weeds"–A Simple Guide to Creating a Healthy Lawn (PDF) —National Coalition for Pesticide-Free Lawns
[Photos, left to right: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org; Richard Old, XID Services, Inc., Bugwood.org; James H. Miller, USDA Forest Service, Bugwood.org; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org; Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org]