Rheum undulatum

Rheum rhabarbarum is a species of flowering plant in the family Polygonaceae, native to southern Siberia to north and central China. It has been harvested from the wild for centuries for its root, which was harvested for use as a popular medicine in Europe and Asia. It was later cultivated for its root in England and Russia. It is considered to be one of the species involved in the development of culinary rhubarb, for which the scientific name R. rhabarbarum is sometimes (erroneously) used. Rheum rhabarbarum was first described by Carl Linnaeus in 1753. Linnaeus also described R. undulatum, but this is now considered to be the same species. The name rha barbarum, Latin for 'foreign rha', was first used in the writings of Celsus, who uses the word to describe a valued medicinal root imported from the east. According to the 2003 key in the Flora of China, this species is distinguished from other entire-leaved rhubarbs in China with leaves having a wavy or crisped margin; R. wittrockii, R. webbianum, R. australe and R. hotaoense, by having less than 1 cm-sized fruit, yellow-white to greenish-white flowers, and the surface of the rachis of panicle covered in papilla. In many characters it is most similar to R. webbianum, and somewhat less so R. hotaoense. There have been at least two studies investigating the karyotypy of this species, both studies focussing on the synonym R. undulatum. Both 2n=22 and 2n=44 have been found. It is possible that this karyotypic diversity indicates the existence of one or more cryptic species, because the polyploid forms would essentially be reproductively isolated. It is native to an area of southeastern Siberia in the Daurian region around and stretching east from Lake Baikal in Russia, and in northern Mongolia. In China, it occurs in the northern provinces of Hebei, Heilongjiang, Henan, Hubei, Jilin, Inner Mongolia, Shanxi and Shaanxi. In China it is known as a species growing on mountain slopes at 1000–1600 m elevation. In Russia it occurs in sandy ground along field edges, on the steppes, and in the regionally uncommon copses of woodland. In China it flowers in June, and has fruit after July.