Unknown wildflower. What is it called?

(Scientific name: Polygonum orientale Linn.) is a plant of the Polygonaceae family. Annual herbs, up to 3 meters high. Stem erect, articulate, hollow. Both surfaces of the leaves have coarse hairs and glandular dots. Racemes terminal or axillary, pendulous; light red or rose-red small flowers in early fall. Born in grassland and swampy places along ditches and rivers. Because of its rapid growth, tall and lush, green leaves, and dense red flowers, adaptable, suitable for ornamental, so suitable for ornamental plants. The fruit is used as medicine, called "water saffron seed", has the effect of activating blood circulation, relieving pain, eliminating accumulation and diuretic. Distributed in North Korea, Japan, Russia, the Philippines, India, Europe and Oceania also have.