I cannot get a clear enough view of the stem of this plant to verify that it is Japanese knotweed. The toothed edges suggest that it might not be.

If it is you are correct, Japanese Knotweed is a nasty aggressive plant. The following websites give information. It is reportable.  You can contact your local agricultural inspector and discuss your theory about where it came from.  Contact Greg Henkel at:

Also see: 

1. https://extension.umn.edu/yard-and-garden-news/japanese-knotweed

2. https://www.dnr.state.mn.us/invasives/terrestrialplants/herbaceous/knotweeds.html



Okay.  I will look forward to receiving the pictures.



None of these appear to be Japanese knotweed.  They do not have the smooth edges on the leaves.  And more important they do not have the nodes that are characteristic on the stems.  I am also guessing that they do not have the hollow stems of Japanese knotweed. See: https://www.minnesotawildflowers.info/flower/japanese-knotweed

They might be aspen seedlings.  See: https://www.minnesotawildflowers.info/tree/quaking-aspen



You are welcome!