Bistorta is a genus of flowering plants in the family Polygonaceae. about 40 species are accepted. It has been supported as a separate clade by molecular phylogenetic analysis. Bistorta species are native throughout much of the Northern Hemisphere, as far south as Mexico in North America and Thailand in Asia. Description Species of Bistorta are perennial herbaceous plants. Their roots are fibrous, forming rhizomes. They have erect, unbranched stems. Their leaves are usually longer than wide, mostly basal, but with some arranged alternately on the stems. The inflorescences are spikelike. The individual flowers have five white to purple-pink (rarely red) tepals. The flowers are bisexual, although the 5–8 stamens are sometimes poorly developed. There are three styles. The fruits are in the form of achenes, that are brown or dark brown, unwinged, and three-angled. The monoploid number of chromosomes, x, is 11 or 12. Taxonomy In 1753, Carl Linnaeus divided up his genus Polygonum into unranked groups, one of which was Bistorta. In 1754, Giovanni Antonio Scopoli elevated Bistorta to a genus. Bistorta is placed in the subfamily Polygonoideae, tribe Persicarieae, along with the genera Koenigia and Persicaria. A 2015 molecular phylogenetic study suggested that the tribes in Polygonoideae were related as shown in the following cladogram. Within the tribe Persicarieae, Bistorta is most closely related to Koenigia: Species , Plants of the World Online accepted the following 42 species. Bistorta abukumensis Yonek., Iketsu & H.Ohashi Bistorta affinis (D.Don) Greene Bistorta albiflora Miyam. & H.Ohba Bistorta alopecuroides (Turcz. ex Besser) Kom. Bistorta amplexicaulis (D.Don) Greene Bistorta attenuata Kom. Bistorta attenuatifolia Miyam. & H.Ohba Bistorta bistortoides (Pursh) Small Bistorta burmanica Yonek. & H.Ohashi Bistorta coriacea (Sam.) Yonek. & H.Ohashi Bistorta diopetes H.Ohba & S.Akiyama Bistorta elliptica (Willd. ex Spreng.) V.V.Petrovsky, D.F.Murray & Elven Bistorta emodi (Meisn.) H.Hara Bistorta griersonii Yonek. & H.Ohashi Bistorta griffithii (Hook.f.) Grierson Bistorta hayachinensis (Makino) H.Gross Bistorta honanensis (H.W.Kung) Yonek. & H.Ohashi Bistorta incana (Nakai) Nakai Bistorta jaljalensis H.Ohba & S.Akiyama Bistorta krascheninnikovii N.A.Ivanova Bistorta longispicata Yonek. & H.Ohashi Bistorta ludlowii Yonek. & H.Ohashi Bistorta macrophylla (D.Don) Soják Bistorta manshuriensis (Petrov ex Kom.) Kom. Bistorta milletii H.Lév. Bistorta milletioides H.Ohba & S.Akiyama Bistorta ochotensis Kom. Bistorta officinalis Delarbre Bistorta paleacea (Wall. ex Hook.f.) Yonek. & H.Ohashi Bistorta perpusilla (Hook.f.) Greene Bistorta plumosa (Small) Greene Bistorta purpureonervosa (A.J.Li) Yonek. & H.Ohashi (Brügger) Dostál Bistorta rubra Yonek. & H.Ohashi Bistorta sherei H.Ohba & S.Akiyama Bistorta sinomontana (Sam.) Miyam. Bistorta