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Knotweed Family (Polygonaceae). Pennsylvania smartweed is an annual herb that has small, five-parted pink or rose colored flowers on a short spike. It grows 2 to 4(6) feet high. The flowering branches have stalked glands. The stems have a reddish color and swollen nodes. The alternate leaves have sheaths extending around the stems. The seeds are black, shiny, flattened, and almost round. There are approximately 62,000 seeds per pound.