It’s considered a noxious weed in most areas, so the “garden police” would be your local county who can fine you in addition to cost for removal on your property anywhere you’ve allowed it to spread. Where I am at it keeps getting spread by flood waters and taking over the entire riparian zone and spreads from there. I would hope people are just trying to troll and aren’t seriously considering planting this intentionally. How about some kuduz while you are at it?

Update: this was definitely japanese knotweed. I went back this spring and there was lots more of it. Dug up as much root as I could and will revisit periodically to get any regrowth. It was not as robust as it might have been due, I suspect, to the level of shade.

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JW has large, unlobed, heart-shaped leaves and hollow cane-like stems And does produce an aggressively creeping rootstock instead of a tight clump of growth. As an aside the common nuisance kind in some areas - including much of the Pacific Northwest and Great Britain - is Bohemian knot-weed rather than Japanese. It is an intermediate hybrid resulting from the crossing of Japanese and giant knot-weeds, with the hybrid plants often being male. So that there is not a problem with these male plants reseeding. Just covering large spaces with their vegetative growth if they are not destroyed. I have seen uncontrolled patches in my area occupying square footage the size of entire building lots - and bigger. If still nobody has done anything about it there is an infested bottom-land in the bend of a river in a National Forest east of here that may be something on the order of an acre in extent.