[1] Members of the genus, including R. japonica (Japanese knotweed) and its hybrid with R. sachalinensis, are highly invasive plants.

[3][4] As with many species in the family Polygonaceae, the taxonomic boundaries of Reynoutria have been much confused; in particular, it has been repeatedly merged with and separated from Fallopia.

and continued through to the late 20th century, with competing arguments based around plant morphology, habit and chemistry.

[6][7] A series of molecular phylogenetic studies have clarified these relationships; Reynoutria is a well-supported monophyletic taxon.

[5] While Muehlenbeckia and Fallopia s.s. are believed to be more closely related, all three share the morphological character of extra floral nectaries.