This is a knotweed, an herbaceous perennial.

Thanks for the suggestion. I read some about knotweed online. The leaves and blossoms do look very much like some type of knotweed but I know it is not the Japanese knotweed because the stems are not hollow and the blossoms are not white. I don't remember if this dies to the ground each winter or not. It has certainly never spread or reseeded itself. I think I need to do some further research. Does anyone else have more information?

This looks like Persicaria 'Crimson Beauty', related to the pernicious knotweed, but a clump former. The flowers start out off white and turn to red. I really love this plant, though the leaves are often badly eaten by Japanese Beetles. It's a stunner in bloom though. And mine is an easy 12 feet tall.

All Fallopia/Persicaria/Polygonum are knotweeds.