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  Japanese knotweed  

Department of Natural Resources

Illinois Exotic Species:
Japanese knotweed Polygonum cuspidatum

Japanese knotweed has the appearance of a shrub, but it is actually an herbaceous perennial plant. It is a native of Asia and Japan that can grow to ten feet in height. Its hollow stems, which are enlarged at the nodes, resemble bamboo. The white flowers are borne in late summer and are very attractive to insects. However, its primary mode of reproduction is by dense rhizomes (underground stems). This plant has been widely planted as an ornamental for the small white flowers which are borne in July and August. Once established, Japanese knotweed is extremely difficult to eradicate. Currently, Japanese knotweed is present along roadsides and ditches, but it has also invaded streamside areas in parts of the state.


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