Japanese Knotweed (Polygonum cuspidatum)

Japanese knotweed is a herbaceous perennial that can reach heights of 9' tall. Semi-woody stems are erect and hollow and resemble bamboo canes.

Leaves: Leaves are dark green and are 4-6" long.

Flowers: There are many small greenish white flowers. These flowers bloom in late summer.

Fruits & Seeds: Seeds are small, shiny, and black. They are enclosed in a winged calyx that makes them buoyant.

Roots: Robust rhizomes grow 6' deep thus creating a dense impenetrable mat.

Ecological threats

  • Japanese knotweed invades forest edges, wetlands, fields, roadsides, and urban areas. It poses a significant threat because it will eliminate vegetation and cause erosion.
  • Young stems can produce new roots and shoots if buried or floating.
  • Japanese knotweed is able to break through pavement and building foundations.