"In Japanese, the name is itadori (虎杖, イタドリ). The kanji expression is from the Chinese meaning 'tiger stick'. One interpretation of the Japanese name is that it

"In Japanese, the name is itadori (虎杖, イタドリ). The kanji expression is from the Chinese meaning 'tiger stick'. One interpretation of the Japanese name is that it comes from 'remove pain' (alluding to its painkilling use), though there are other etymological explanations offered." (https://en.wikipedia.org/wiki/Reynoutria_japonica https://en.wikipedia.org/wiki/Reynoutria_japonica)