Fallopia japonica, synonym Reynoutria japonica, commonly known as Japanese knotweed, is a large, herbaceous perennial plant of the knotweed and buckwheat family Polygonaceae. It is native to East Asia in Japan, China and Korea. In North America and Europe the species is very successful and has been classified as an invasive species in several countries. In Australia, it is illegal to have any of this species growing on one's property.