Southeastern Wisconsin Invasive Species Consortium, Inc.


Shop Local

Japanese knotweed

Japanese knotweed

Japanese knotweed

(Fallopia japonica or Polygonum cuspidatum)

General description:

Japanese knotweed is an herbaceous perennial that forms large colonies of erect, arching stems (resembling bamboo). Stems are round, smooth, and hollow with reddish-brown blotches. Plants reach up to 10’ and the dead stalks remain standing through the winter.

Ecological threat:

  • New infestations of Japanese knotweed often occur when soil contaminated with rhizomes is transported or when rhizomes are washed downstream during flooding.
  • Poses a significant threat to riparian areas where it prevents streamside tree regeneration, and increases soil erosion.
  • Root fragments as small as a couple inches can resprout, producing new infestations.
  • Disrupts nutrient cycling in forested riparian areas.
  • Plants contain allelopathic compounds (chemicals toxic to surronding vegetation).
Photo Gallery: