Polygonum cuspidatum, Polygonum x bohemicum, Polygonum sachalinense

Perennial; small, white to green flowers in drooping clusters from leaf axils. Reddish brown and hollow stems. Leaves broad and ovate.

knotweed flowers

Photo credit: Jan Samanek

Japanese knotweed leaves

Photo credit: Nanna Borcherdt

Japanese knotweed stem

Photo credit: Chris Evans

Japanese knotweed leaf

Photo credit: Steve Manning

Japanese knotweed whole plant

Photo credit: Randy Westbrooks

  • knotweed flowers
  • Japanese knotweed leaves
  • Japanese knotweed stem
  • Japanese knotweed leaf
  • Japanese knotweed whole plant

Plant Details

Habitat:

Near water sources, along streams and rivers, wetlands, riparian areas and roadsides.
Mature Height:
6.5-13’
Target Audience:
water, garden clubs, water gardens
ODA Listing:
B
Plant Look Alikes:
Bamboo, other knotweeds, common pokeweed
Plant Impacts:
Spreads quickly and forms dense thickets that displace native vegetation due to its aggressive growth. Creates bank erosion problems and is considered a potential flood hazard. Lowers quality of riparian habitat for fish and wildlife. Extremely vigorous rhizomes form deep, dense mat. Plants resprout from stem or root fragments creating new infestations downstream.
Plant Links:
King County Knotweed Info
CWMA Actions List:
volunteer response, contractor response