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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 designated in the Alberta Weed Control Act. Prohibited noxious weeds must be destroyed when found, 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 (edge of leaf closest to main stalk is perpendicular to the leaf stem) 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. The plant can be described as “shrub-like” with numerous stems in a clump.  Shoots first appear coloured red to
purple but turn green as they grow.

The seeds are 2.5 mm long, triangular, and shiny.  They are enclosed in a somewhat heart-shaped papery winged covering and are wind dispersed.

Learn more about this species:

SeeFact Sheets - Alberta Invasive Species Council

For More Information

Weed Management

Telephone

In Edmonton: 311

Outside Edmonton: 780-442-5311

Email invasiveweeds@edmonton.ca

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