Rheum (plant)

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Rheum
Rheum rhabarbarum.2006-04-27.uellue.jpg
Scientific classification e
Kingdom: Plantae
Clade: Angiosperms
Clade: Eudicots
Order: Caryophyllales
Family: Polygonaceae
Subfamily: Polygonoideae
Genus: Rheum
L.
Species

See text.

Synonyms[1]
  • Rhabarbarum Fabr.

Rheum[2] is a genus of about 60 herbaceous perennial plants in the family Polygonaceae. Species are native to eastern Europe, southern and eastern temperate Asia, with a few reaching into northern tropical Asia. Rheum is cultivated in Europe and North America.[1] The genus includes the vegetable[3] rhubarb. The species have large somewhat triangular shaped leaves with long, fleshy petioles. The flowers are small, greenish-white to rose-red, and grouped in large compound leafy inflorescences. A number of cultivars of rhubarb have been domesticated both as medicinal plants and for human consumption. While the leaves are toxic, the stalks are used in pies and other foods for their tart flavor.

Description[edit]

Rheum ribes growing in Iran

Rheum species are herbaceous perennials growing from fleshy roots. They have upright growing stems and mostly basal, deciduous leaves growing from short, thick rhizomes. They have persistent or deciduous ocrea. The inflorescences are terminal and panicle-like with pedicels. The hermaphrodite flowers consist of a whitish green to pinkish green, hairless and campanulate (bell-shaped) perianth, composed of six tepals. The outer three tepals are narrower than the inner three and all are sepal-like in appearance. The flowers have nine (sometimes six) stamina inserted on the torus at the base of the peranthium, they are free or subconnate at their base. The anthers are yellow or pinkish green, elliptic in shape. The ovary is simple and triangular shaped with three erect or deflexed styles. The stigmas are head-like. The fruits are a three-sided achene with winged sides, and the seeds are albuminous with a straight or curved embryo.

Seeds

Taxonomy[edit]

The genus Rheum was erected in 1753 by Carl Linnaeus,[4] initially for three species: R. rhaponticum, R. rhabarbarum and R. ribes.[5] Linnaeus did not explain the origin of the genus name. Rheum is usually derived from the Greek rheon,[6][7] mentioned by Dioscorides as an alternative name for medicinal rhubarb; the word rheon is itself thought to be derived from the (old) Persian rewend.[7] Dioscorides calls the plant rha, but mentions the Romans call it rha ponticum, and it was also called ria or rheon.[8] It is theorised the Ancient Greek word rha was derived from an ancient Scythian name for the Volga River in Russia, , near from where the plant was supposedly brought.[8][9][10] (See Volga River § Nomenclature.)

Rheum is placed in the family Polygonaceae, subfamily Polygonoideae. Within the subfamily, it is in the tribe Rumiceae, along with the two genera Oxyria and Rumex. It is most closely related to Rumex.[11]

Rumiceae

Oxyria

Rumex

Rheum

Species[edit]

The genus is represented by about 50–60 extant species.[1][12] The many cultivars of culinary rhubarb more usually grown for eating are recognised as Rheum × hybridum in the Royal Horticultural Society's list of recognised plant names. The drug rheum is prepared from the rhizomes and roots of another species, R. officinale or medicinal rhubarb. This species is also native to Asia, as is the turkey rhubarb, R. palmatum. Another species, the Sikkim rhubarb, R. nobile, is limited to the Himalayas.

As of March 2019, Plants of the World Online recognized the following species:[1]

Other species within this genus that have been recognized include:[13]

Ecology[edit]

Rheum species have been recorded as larval food plants for some Lepidoptera species including brown-tail, buff ermine, cabbage moth, large yellow underwing, and nutmeg moth.[citation needed]

Uses[edit]

Many rheum species have food and medicinal uses. Some of these uses originated in Asia more than 2,000 years ago. All parts of the plant contain slightly poisonous oxalic acid, but its concentration in the leaf stems or petioles used in food preparation is very low, and their tart flavor instead is caused by nontoxic malic acid. The plants also produce other compounds, including citric acid and anthraquinone glycosides, and the raw or cooked leaf blades are poisonous to humans and livestock if consumed in large enough amounts.[14] Plants in cultivation are propagated by cutting up the crowns of larger plants and by seeds.

Some species are grown for their ornamental qualities, including R. acuminatum, R. alexandrae, R. australe, R. kialense, R. palmatum, R. rhabarbarum and R. ribes.[15]

References[edit]

  1. ^ a b c d "Rheum L.". Plants of the World Online. Royal Botanic Gardens, Kew. Retrieved 2019-03-10.
  2. ^ From Ancient Greek ῥῆον.
  3. ^ Vegetable Crops Production Guide for the Atlantic Provinces[dead link]
  4. ^ "Plant Name Details for Rheum L." The International Plant Names Index. Retrieved 2019-03-12.
  5. ^ Linnaeus, Carolus (1753). "Rheum ribes". Species Plantarum, Tomus I. Stockholm: Impensis Laurentii Salvii. Retrieved 2019-03-11.
  6. ^ Hyam, R. & Pankhurst, R.J. (1995). Plants and their names : a concise dictionary. Oxford: Oxford University Press. ISBN 978-0-19-866189-4.
  7. ^ a b Dunstone, Denis (2014). Why is an Apple a Pomme? A Journey with Words. Lulu Publishing Services. ISBN 978-1-4834-1859-9.
  8. ^ a b Osbaldeston, Tess Anne; Wood, RPA (2000). Dioscorides - De Materia Medica. Johannesburg: Ibidis Press. p. 364, 367. ISBN 0-620-23435-0.
  9. ^ J.P. Mallory & D.Q. Adams, Encyclopedia of Indo-European Culture, s.v. "dew" (London: Fitzroy Dearborn, 1997), 158-9.
  10. ^ Johnson, A.T. & Smith, H.A. (1972). Plant Names Simplified : Their Pronunciation Derivation & Meaning. Buckenhill, Herefordshire: Landsmans Bookshop. ISBN 978-0-900513-04-6.
  11. ^ Schuster, Tanja M.; Reveal, James L.; Bayly, Michael J. & Kron, Kathleen A. (2015). "An updated molecular phylogeny of Polygonoideae (Polygonaceae): Relationships of Oxygonum, Pteroxygonum, and Rumex, and a new circumscription of Koenigia". Taxon. 64 (6): 1188–1208. doi:10.12705/646.5.
  12. ^ Wang, A.; Yang, M; Liu, J (2005). "Molecular Phylogeny, Recent Radiation and Evolution of Gross Morphology of the Rhubarb genus Rheum (Polygonaceae) Inferred from Chloroplast DNA trnL-F Sequences". Annals of Botany. 96 (3): 489–98. doi:10.1093/aob/mci201. PMC 4246783. PMID 15994840.
  13. ^ The Plant List
  14. ^ Rheum rhabarbarum in Flora of North America @. Efloras.org. Retrieved on 2015-05-02.
  15. ^ Jelitto, Leo; Baumgardt, John Philip; Schacht, Wilhelm; Fessler, Alfred; Epp, Michael E.; Vol 2 (1990). Hardy herbaceous perennials. Portland, Or.: Timber Press. p. 555. ISBN 0-88192-159-9.CS1 maint: Multiple names: authors list (link)