Knotgrass

...In the narrow sense, it refers to Polygonum serrata, and in the broad sense, it refers to plants similar to Polygonum serrata (such as Polygonum serrata, Polygonum sakuraensis, and Polygonum onata) in the Polygonaceae family. Polygonum serrata (water pepper) (illustration), whose leaves are spicy and which gave rise to the expression "Even the water pepper-eating insects love it," is an annual plant in the Polygonaceae family. It is also called Polygonum serrata or Polygonum hontade, and means true Polygonum serrata with spicy leaves.

*Some of the terminology explanations that mention "Knotgrass" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…狭義にはヤナギタデをさし，広義にはタデ科タデ属Polygonum(英名smartweed,knotgrass,knotweed)のヤナギタデに類似した植物(イヌタデ，サクラタデ，オンタデなど)を総称する。　〈蓼食う虫も好き好き〉の語源となった葉の辛いヤナギタデP.hydropiper L.(英名water pepper)（イラスト）はタデ科の一年草で，マタデ，ホンタデとも呼ばれ，葉の辛い真正のタデを意味する。…

※「Knotgrass」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報