Rheum palmatum

Rheum palmatum

Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Order:	Caryophyllales
Family:	Polygonaceae
Genus:	Rheum
Species:	R. palmatum
Binomial name
*Rheum palmatum* L.

Rheum palmatum is a species of flowering plant in the knotweed family Polygonaceae. It is commonly called Chinese rhubarb,^[1]^[2] ornamental rhubarb,^[3] Turkey rhubarb^[2] or East Indian rhubarb.^[2]

Rheum palmatum is a herbaceous perennial related to the edible rhubarb. It is primarily used in traditional medicine, and as an ornamental subject in the garden.

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Taxonomy

Agnia Losina-Losinskaja proposed classifying it in the section Palmata in the Flora SSSR in 1936.^[4] In the 1998 Flora Republicae popularis Sinicae A. R. Li maintains this classification for this species.^[5]

Description

Its lobed leaves are large, jagged and hand-shaped, growing in width to two feet. Chinese rhubarb has thick, deep roots.^[6]

Similar species

The species Rheum tanguticum is closely related to R. palmatum.^[7]

R. palmatum can be distinguished from R. × hybridum, the garden rhubarb we eat, by size; while garden rhubarb only grows to a few feet in height, Chinese rhubarb can grow to six feet.^[6]

Karyotypy

R. palmatum has a chromosome count of 2n=22.^[5]

Distribution

It is native in the regions of western China, northern Tibet, and the Mongolian Plateau.^[6]

Folk medicine

Rheum tanguticum, Rheum palmatum, R. rhabarbarum and R. officinale and a few others, are all harvested for their roots, which are used as a herbal medicine.^[7] Rheum palmatum (or dahuang) is an important crop that has been used in traditional Chinese medicine for over 2,000 years.^[8]

The dried roots of Chinese rhubarb became one of the most prominent items traded along the Silk Road.^[6] Imported roots of various rhubarb species were widely used in Europe for hundreds of years before the identity of the plant was eventually discovered.^[6] Some of the common names associated with Rheum palmatum – "Russian rhubarb", "Turkey rhubarb", and "Indian rhubarb" – are directly affiliated with the trade routes for rhubarb from China.^[6]

The root is known for its purported purging effects and suppressing fever.^[6] In ancient China, rhubarb root was taken to try to cure stomach ailments and as a "cathartic" (an agent used to relieve constipation), and used as a poultice for "fevers and edema" (swelling caused by fluid retention in the body tissues).^[6] It was given its Latin name by Carolus Linnaeus in the year 1759 and first grown in Britain around 1762.^[6]

The first International Symposium on Rhubarb was held in China in 1990. Its objective was to verify the scientific data and treatment of Chinese Rhubarb used by Chinese pharmacopoeias.^[6]

Health risks

Pregnant women should avoid all intake of the plant since it may cause uterine stimulation.^[6] If taken for an extended amount of time, adverse effects include: "hypertrophy of the liver, thyroid, and stomach, as well as nausea, griping, abdominal pain, vomiting, and diarrhea."^[6]

Though the root of the Chinese rhubarb is a key facet of herbal medicine, its leaves can actually be poisonous if consumed in large amounts due to the oxalic acid content.^[6] Patients with "arthritis, kidney problems, inflammatory bowel disease, or intestinal obstruction" should refrain from consumption.^[6]

Cultivation

Ornamental use

With its large palmate leaves and tall panicles of pink flowers, Rheum palmatum is a bold statement plant for the temperate garden, that grows up to 2.5 m (8.2 ft) tall and broad. It is hardy down to −20 °C (−4 °F).^[9] It is propagated by seed in the spring, or by root division in spring or autumn.^[7] It grows best in full sunlight in well-drained soil.^[7]

The following cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-^[10]

'Ace of Hearts'^[11] – compact cultivar to 1.5 m (4.9 ft)
'Bowles's Crimson'^[12]
'Hadspen Crimson'^[13]

Farming as medicinal herb

Since it is the roots and rhizome which serve as this plant's source of medicinal usage, special care is taken in their preparation.^[6] When 6–10 years old, the rhizomes of these plants are removed from the ground in the autumn when both its stems and leaves changed to yellow wild.^[7] Furthermore, the removal of the lateral rootlets and the crown are removed, leaving only the root.^[7] Any debris around the root is cleaned off, the coarse exterior bark removed, and the root cut and divided into cube-like pieces to increase its surface area, thereby decreasing the time needed for drying.^[6]

References

^ USDA, NRCS (n.d.). "Rheum palmatum". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 1 February 2016.
^ ^a ^b ^c Eisenreich, Dan (1996–2010). "Rhubarb Botanical Information". The Rhubarb Compendium. Retrieved 2011-02-07.
^ BSBI List 2007 (xls). Botanical Society of Britain and Ireland. Archived from the original (xls) on 2015-06-26. Retrieved 2014-10-17.
^ Лозина-Лозинская, Агния Сергеевна (1936). "Rheum". In Комаро́в, Влади́мир Лео́нтьевич (ed.). Flora SSSR, Vol. 5 (in Russian). Moscow: Издателство Академии Наук СССР. pp. 500–501.
^ ^a ^b 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 ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p Foster, Steven (2006). Desk Reference to Nature's Medicine. Washington, D.C.: National Geographic Society. pp. 104–105. ISBN 0-7922-3666-1.
^ ^a ^b ^c ^d ^e ^f Chevallier, Andrew (2000). Natural Health: Encyclopedia of Herbal Medicine. New York: Dorling Kindersley. pp. 127. ISBN 0-7894-6783-6.
^ Piątek, Marcin; Lutz, Matthias; Wang, Yan; Wang, Shengrong; Kellner, Ronny (August 2021). "Thecaphora dahuangis, a new species causing leaf smut disease of the traditional medicinal plant dahuang (Rheum palmatum) in China". Plant Pathology. 70 (6): 1292–1299. doi:10.1111/ppa.13385.
^ "RHS Plantfinder – Rheum palmatum". Retrieved 23 September 2018.
^ "AGM Plants – Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 84. Retrieved 27 September 2018.
^ "RHS Plantfinder – Rheum 'Ace of Hearts'". Retrieved 23 September 2018.
^ "RHS Plantfinder – Rheum palmatum 'Bowles's Crimson". Retrieved 23 September 2018.
^ "RHS Plantfinder – Rheum palmatum 'Hadspen Crimson'". Retrieved 23 September 2018.