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
Hybrid Japanese knotweed is a hybrid between giant knotweed and Japanese knotweed and was introduced as a garden plant.
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.
A hybrid between Japanese knotweed and giant knotweed, Hybrid Japanese knotweed 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.
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.