I've got a large patch of that in my backyard and have wondered what it is - thanks!

I've also got japanese knotweed (it's not just for rivers anymore) and some himalya blackberry (almost gone, phew). Oh, and english ivy of course. There are few more, but I can't remember the names. This is on a 25' x 40' lot, half of which is covered by house. Perhaps I'll just see how many invasives I can cram into one space and let them battle each other for top billing. Who will be America's Next Most Invasive (plant) Species?