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Japanese Knotweed

Japanese knotweed
Photo Credit: Leslie Mehrhoff, University of Connecticut, Retrieved from Bugwood.org (Image Number: 2308046), used under CC BY 3.0 US, modified from the original

Common Name: Japanese Knotweed

Scientific Name: Fallopia japonica

Habitat: disturbed areas, grassland wet, forests - wet areas, forests - open areas, forest edges, ditches

Provincial Designation: Prohibited Noxious

Prohibited Noxious weeds are plant species that are designated as "prohibited noxious" in the Alberta weed regulation. Prohibited noxious weeds must be destroyed, meaning all growing parts need to be killed or the plant's reproductive mechanisms need to be rendered non-viable.

Origin

Japanese knotweed is native to Japan and was introduced to North America as an ornamental and as landscape screening in the late 1800s.

Legislated Because

This species forms dense stands that shade and crowd out native vegetation causing a loss or alteration of wildlife habitat, especially along waterways. It can also sprout through asphalt and small cracks in concrete causing structural damage to foundations and roads.

Description

Japanese knotweed has small white flowers that are 3-5 mm wide and clustered together in showy, often upright sprays along the branches.

The leaves are egg-shaped or elliptic with have a distinct truncate base and grow up to 15 cm long and 10 cm wide. The undersides of leaves are covered in stiff, 0.2 mm long hairs.

The stems are round and hollow and grow up to 2 m tall.