The Giant knotweed (Reynoutria sachalinensis) belongs to Polygonaceae (the Knotweed family). It is a perennial herb that is distributed northward from Chubu district of Honshu to Hokkaido, as well as the Kuril Islands and Sakhalin. This herb grows in montane to sub-alpine screes and can reach 1-3 m in height. It is dioecious. The leaves are long-ovate to ovate, 15-30 cm long and 10-20 cm across. The leaves are powdery white on abaxial sides and have short hairs on veins. The racemes are borne on the upper axiles and bloom white flowers from July to September. The young shoot have a sour taste and edible. The rootstocks are used a herbal medicine for laxative and diuretic agent.