Abstract: The sequences of chloroplast trnL-F (including 19 species and 1 varieties) and matK (including 16 species and 1 varieties) regions of 4 genera from Polygonaceae were compared and analyzed to examine the systematic position of Reynoutria Houtt. and Polygonum sibiricum Laxm. The genus Rheum L. from subfamily Rumicoideae was designated as the outgroup. From the two strict consensus trees it was inferred that: (1) the genus Reynoutria was a member of the genus Fallopia with high bootstrap support; (2) Polygonum sibiricum Laxm. was separated from Polygonum and adjacent to genus Fallopia, so this species should be raised to the genus rank and can be called Knorringia sibirica (Laxm.) Tzvel. Moreover, the boundary of the two genera was defined in this article.

Key words: matK sequences, phylogenetics, Polygonum sibiricum, Reynoutria Houtt., trnL-Fsequences