Fallopia japonica

Fallopia japonica_Japanese knotweed_CDFA_cropped
Photo: CDFA

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 — Alert?

CDFA Rating: A*?


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.

Species ID Card

Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.

Special Reports

Resources for ID and potential "look-alikes" from UC Agriculture and Natural Resources, with the Marin Knotweed Action Team

Weed 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

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

Other Fallopia japonica Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - Distribution map and records of this species in California.
  • CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
  • EDDMapS - Distribution of this species in North America.
  • Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.
  • Additional photos

    Fallopia japonica_flowers_KeirMorse
    Fallopia japonica (Japanese knotweed) flowers. Photo: Keir Morse
    Fallopia japonica_inflorescences_KeirMorse
    Fallopia japonica (Japanese knotweed) inflorescences. Photo: Keir Morse
    Fallopia japonica_leaves and stem_KeirMorse
    Fallopia japonica (Japanese knotweed) leaves and stem. Photo: Keir Morse