Koenigia weyrichii
Koenigia weyrichii, the Chinese knotweed or Weyrich's knotweed, is a large, perennial, rhizomatous herb native to northeastern Asia in Kamchatka, Sakhalin, and northern and central Japan. It is also locally naturalised in northern Europe.
It is one of the parents of the cultivated hybrid Koenigia × fennica, the other being Koenigia alpina.