Hybrid Japanese Knotweed

Hybrid Japanese Knotweed Photo Credit: Leslie Mehrhoff, University of Connecticut, retrieved from Bugwood.org (Image Number: 5446741), used under CC BY 3.0 US, modified from the original

Common Name: Hybrid Japanese Knotweed

Scientific Name: Fallopia x bohemica

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

Hybrid Japanese Knotweed is a hybrid between Giant Knotweed and Japanese Knotweed and was introduced as a garden plant.

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

This hybrid shares characteristics of both parent species. Hybrids are highly variable in appearance therefore, several characteristics need to be considered to ensure correct identification.

The flowers are 3-5 mm wide and clustered together in showy, often upright sprays along the branches. The leaves can be heart-shaped, elliptic, or egg-shaped with a more or less truncate base (end of the leaf closest to the main stem is perpendicular to the leaf stalk).

The leaf size can vary between 15-30 cm length and 10-25 cm width. The undersides of leaves are covered in stiff, 0.2 mm long hairs.

The stems are hollow and grow up to 4 m tall.

Roots can extend 2-7 m away from the main stem. Fragments as light as dime can generate new plants.