Weed Department
Idaho State Noxious 
Weed Law
Japanese Knotweed


General Description: It is a perennial species with spreading rhizomes and numerous reddish-brown, freely branched stems. Plants can reach 4 to 8 feet in height and is often shrubby.

Flower Description: The whitish to whitish-green flowers are in drooping panicles (clusters) from leaf axils. Male and female flowers are on separate plants.

Leaf Description: Leaves are alternately arranged with petioles (stalks) and are 4 to 6 inches long, ovate and have a truncated base and an abrupt tip.

Stem Description: Stems are upright, branching and deciduous.

Fruit/Seed Description: The fruits are approximately 1/8 inch long, shiny brown and triangular.


Interesting Facts:

It is a very aggressive escaped ornamental that is capable of forming dense stands, crowding out all other vegetation and degrading wildlife habitat. It can also create a fire hazard in the dormant season. It is difficult to control once established.