Japanese Knotweed (Polygonum cuspidatum) 2016-5-18 John Heinz NWR at Tinicum, PA

I'm not 100% sure about this, although it's likely.
Idenitification tips on the four most likely to be confused with each other:
-Bohemian knotweed (P. x bohemicum)
-Japanese knotweed P. cuspidatum)
-Giant knotweed (P. sachalinense)
-Himalayan knotweed (P. polystachyum)
at this site:
http://www.kingcounty.gov/environment/animals-and-plants/noxious-weeds/weed-identification/invasive-knotweeds.aspx
and more info at:
http://www.fs.fed.us/database/feis/plants/forb/polspp/all.html