Fallopia japonica

Photo courtesy Joseph DiTomaso

Synonyms: Polygonum cuspidatum; Reynoutria japonica, Fallopia baldschuanica

Common names: Japanese knotweed; Mexican bamboo

Fallopia japonica (=Polygonum cuspidatum) (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.

Cal-IPC Rating: Moderate

Cal-IPC Assessment

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.

Weed RIC Management Notes

  • Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

Cal-IPC Symposium Presentations

There are no Symposium presentations associated with this species yet.

Other Fallopia japonica Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - See the distribution of this species on Calflora's map of California.
  • Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • CDFA - California official noxious weeds.
  • USDA PLANTS Database - Federal database with information on identification and distribution, and links to websites in individual states.