John Pitarresi in a "Special to the Observer-Dispatch" declared that "Japanese knotweed is a menace.Even more than we knew. Knotweed is that tall, big-leafed plant that grows most commonly along creeks and rivers in dense stands that can be almost impossible to walk through. Some call it bamboo, which it superficially resembles. It makes recreation in some areas very difficult, and it displaces native plants in a big way. And more than that."
Pitarresi then continues to name a number of other invasive species, many of which were introduced on purpose. His article is well worth reading. Check it out.