Species: Mile-a-Minute weed

Mile-a-Minute weed, Polygonum perfoliatum / Persicaria perfoliata, Polygonaceae, a photo by Vilseskogen on Flickr.

This plant is a horrible invader, grows nearly as fast as its name indicates. But the blue berries are pretty. Probably eaten by birds, I would think. The stems have these sharp hooks on them, which helps the plant to climb up. It is in the same family as rhubarb, smartweed, and buckwheat, the Polygonaceae.
(Polygonum perfoliatum = Persicaria perfoliata, Polygonaceae)