Source: California Invasive Plant Council

URL of this page:

Polygonum cuspidatum (=Fallopia japonica) (Japanese knotweed)

Polygonum cuspidatum (=Fallopia japonica)
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)

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)