Polygonum cuspidatum (=Fallopia japonica) (Japanese knotweed)

Polygonum cuspidatum (=Fallopia japonica)

Photo courtesy Joseph DiTomaso

Polygonum cuspidatum (=Fallopia japonica) (Japanese knotweed) is a perennial forb/herb (family Polygonaceae ). Plants grow vigorously and create dense colonies that exclude other vegetation. Established colonies are extremely difficult to eradicate. It inhabits disturbed moist sites, roadsides, riparian and wetland areas. Plants typically grow in open, sunny areas on moist soils in cool temperate climates. There is very little of this species in California, but it is spreading rapidly in the Northwest and has been a major problem in the southern and northern US, as well as Europe.

Jepson Manual, 2nd Edition: Fallopia japonica

Cal-IPC Inventory rating: Moderate

Cal-IPC Resources on Polygonum cuspidatum (= Fallopia japonica)

• California Invasive Plant Inventory Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.
• CalWeedMapper - Statewide maps, climate models, and reports.
• Cal-IPC News - Articles from our quarterly newsletter. Each issue is available as a pdf. List of articles on Polygonum cuspidatum.
• Cal-IPC Symposium Proceedings - Presentations and papers from our annual Symposium. List of articles on Polygonum cuspidatum.

Cal-IPC News Articles

• Brusati, E. (2005). Japanese knotweed (Polygonum cuspidatum) and other knotweeds. Cal-IPC News. 13: 10.

Cal-IPC Symposium Proceedings

• Crockett, R. P. and M. L. Krebsbach (2004). The new “JK Injection Tool” for control of knotweeds and other hollow-stem plants growing in sensitive wetland sites. California Invasive Plant Council Symposium 2004. Ventura, CA.
• DiTomaso, J. M. (2005). Efficacy and safety of new herbicides on the horizon. California Invasive Plant Council Symposium 2005. Chico, CA.
• Tu, M. and J. M. Randall (2003). 2003 Cal-IPC red alert! New invasions, recent expansions, and a few others to be on the look-out For. California Invasive Plant Council Symposium 2003. Kings Beach, CA.

Other Resources on Polygonum cuspidatum (=Fallopia japonica)

• USDA PLANTS database - Federal database with information on identification and distribution, and links to websites in individual states.
• Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from the UC Berkeley Jepson Herbarium.
• CalFlora - Distribution information by county based on submitted observations and herbarium specimens.
• The Nature Conservancy Management Summary - Information compiled by TNC land managers. Photos included for some species.
• Encycloweedia - Plants rated as noxious weeds by the California Department of Food and Agriculture.
• CalPhotos - Images of plants taken mostly in California.

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