Bistorta
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.