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Rheum rhabarbarum
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Order:	Caryophyllales
Family:	Polygonaceae
Genus:	Rheum
Species:	R. rhabarbarum
Binomial name
	Rheum rhabarbarum; L.
Synonyms
	Rheum franzenbachii Münter ; Rheum franzenbachii var. mongolium Münter ; Rheum macropterum Mart. ; Rheum muricatum Blanco ; Rheum sanguineum Meisn. ; Rheum undulatum L. ; Rheum undulatum var. longifolium C. Y. Cheng & T. C. Kao ;

Rheum rhabarbarum is a species of flowering plant in the family Polygonaceae, native to a region stretching from southern Siberia to north and central China.^[1] 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.

Taxonomy

Rheum rhabarbarum was first described by Carl Linnaeus in 1753.^[3] Linnaeus also described R. undulatum, but this is now considered to be the same species.^[1]

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.^[4]

Description

Similar species

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.^[5]

Karyotypy

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.^[6]

Distribution

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.^[7]^[8] In China, it occurs in the northern provinces of Hebei,^[2]^[9] Heilongjiang,^[2]^[9] Henan,^[9] Hubei,^[2]^[9] Jilin,^[2]^[9] Inner Mongolia,^[2]^[9] Shanxi^[2]^[9] and Shaanxi.^[9]

Habitat & ecology

In China, it is known as a species growing on mountain slopes at 1,000–1,600 m elevation.^[2] In Russia it occurs in sandy ground along field edges, on the steppes, and in the regionally uncommon copses of woodland.^[7]

In China, it flowers in June, and has fruit after July.^[2]

Most documented insect relationships with this species are muddied by the misapplication of the name R. rhabarbarum to plants of R. × hybridum. As such, most of the insects which are said to use this species as a food plant are generalists from Europe or North America which did not actually eat this species nor are native to the region where this species occurs. An exception is the butterfly Lycaena violacea, whose caterpillars are only known to feed on R. rhabarbarum and whose range is concurrent with that of its host plant (most Lycaena spp. are specialised on Polygonaceae). Cosmia trapezina var. exigua is roughly native to some of the same areas, and its European variety has been found to have eaten rhubarb in Finland (it usually feeds on various tree species). Other species found to eat (garden) rhubarb which occur in the native range of this plant are Arctia caja, Hydraecia micacea, Spilarctia luteum and Xestia baja.^[10]

Cultivation

Rheum rhabarbarum (syn. R. undulatum) was one of a number of distinct species grown in Europe before the beginning of the 18th century. Initially the roots of a related species, possibly R. rhaponticum, were used for medicinal purposes. A putative hybrid of unknown origin, Rheum × hybridum, was also grown. The three taxa were grown as vegetable crops in England and Scandinavia by the early 18th century. They readily hybridize, and culinary rhubarb was developed by selecting open-pollinated seed, so that its precise origin is almost impossible to determine.^[11] In appearance, culinary rhubarb varies continuously between R. rhabarbarum and R. rhaponticum. Modern rhubarb cultivars are tetraploids with 2n = 44, in contrast to 2n=22 for the wild species such as R. rhaponticum.^[12]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h "Rheum rhabarbarum L.", Plants of the World Online, Royal Botanic Gardens, Kew, retrieved 2019-03-10
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Bojian (包伯坚), Bao; Grabovskaya-Borodina, Alisa E. (2003). "Rheum rhabarbarum". In Zhengyi (吴征镒), Wu; Raven, Peter H.; Deyuan (洪德元), Hong (eds.). Flora of China, Vol. 5. Beijing: Science Press. p. 343.
^ "Plant Name Details for Rheum rhabarbarum L.", The International Plant Names Index, retrieved 2019-03-10
^ Alam, Shamshad; Khan, Naeem A. (2015). "Rhubarb (Rewand), A Review" (PDF). Hamdard Medicus. 58 (1): 84–96. Retrieved 13 March 2019.
^ Bojian (包伯坚), Bao; Grabovskaya-Borodina, Alisa E. (2003). "Rheum". In Zhengyi (吴征镒), Wu; Raven, Peter H.; Deyuan (洪德元), Hong (eds.). Flora of China, Vol. 5. Beijing: Science Press. p. 341.
^ Ruirui, Liu; Wang, Ailan; Tian, Xinmin; Wang, Dongshi; Liu, Jianquan (2010). "Uniformity of karyotypes in Rheum (Polygonaceae), a species-rich genus in the Qinghai-Tibetan Plateau and adjacent regions". Caryologia Firenze. 63 (1): 82–90. doi:10.1080/00087114.2010.10589711. S2CID 86616077. Retrieved 24 March 2019.
^ ^a ^b Смекалова, Т.Н.; Ушакова, Р.С. (19 October 2004). "AgroAtlas - Дикие родичи культурных растений - Ареал Rheum rhabarbarum L. (Ревень волнистый)". AgroAtlas, Interactive Agricultural Ecological Atlas of Russia and Neighboring Countries (in Russian). Retrieved 16 March 2019.
^ Smekalova, T.N. "AgroAtlas - Relatives - Rheum rhabarbarum L. - Wavy Rhubarb". AgroAtlas, Interactive Agricultural Ecological Atlas of Russia and Neighboring Countries. Retrieved 15 March 2019.
^ ^a ^b ^c ^d ^e ^f ^g ^h "Species Catalogue of China, Plants". 中国生物物种名录植物卷 (in Chinese). Beijing: Science Press. 2017. Retrieved 15 March 2019.
^ Savela, Markku (27 September 1998). "Rheum". Lepidoptera and some other life forms. Markku Savela. Retrieved 16 March 2019.
^ Tanhuanpää, Pirjo; Suojala-Ahlfors, Terhi & Hartikainen, Merja (2019), "Genetic diversity of Finnish home garden rhubarbs (Rheum spp.) assessed by simple sequence repeat markers", Genetic Resources and Crop Evolution, 66 (1): 17–25, doi:10.1007/s10722-018-0692-8, S2CID 52821042
^ Libert, Bo & Englund, Roger (1989). "Present Distribution and Ecology of Rheum rhaponticum (Polygonaceae)". Willdenowia. 19 (1): 91–98. JSTOR 3996925.