Knotweed, also known as bitter stick, spotted stick and other names, is the dry rhizome and root of Polygonaceae perennial herb Polygonum cuspidatum, which is excavated in spring and autumn. It is not only an ornamental plant, but its tender stems can also be eaten as vegetables. Its roots can be used as cold drinks, and its rhizomes can often be used to make Chinese herbal medicine noodles.

This story was published in the "Park Houseediting" written by Fang Shao in the Song Dynasty, and also in "Introduction to Medicine" compiled by Li Bing in the Ming Dynasty.