I’m guessing that this is Persicaria maculosa, lady’s-thumb smartweed, but there are many similar species:
The flowers are attractive seen close up, but otherwise this plant really is weedy. I pull it up armfuls of it in my garden, year after year. It’s a native plant (if my ID is correct), I’ve read that Native Americans used it to cure poison ivy. Taken at high magnification and stacked.