Prunus

Prunus
Prunus cerasus (Sour Cherry) in bloom
Scientific classification
Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Order:	Rosales
Family:	Rosaceae
Subfamily:	Prunoideae or Spiraeoideae[1]
Genus:	Prunus L.
Species
see text
Synonyms
Amygdalopersica Daniel Amygdalophora M.Roem. Amygdalopsis M.Roem. Amygdalus L. Armeniaca Scop. Cerapadus Buia Ceraseidos Siebold & Zucc. Cerasus Mill. Emplectocladus Torr. Lauro-cerasus Duhamel Laurocerasus M.Roem. Maddenia Hook.f. & Thomson Padellus Vassilcz. Padus Mill. Persica Mill. Pygeum Gaertn.

Prunus is a genus of trees and shrubs, which includes the plums, cherries, peaches, apricots and almonds. Within the rose family Rosaceae, it was traditionally placed as a subfamily, the Prunoideae (or Amygdaloideae), but was sometimes placed in its own family, the Prunaceae (or Amygdalaceae). More recently it has become apparent that Prunus evolved from within subfamily Spiraeoideae.^[1] There are around 430 species spread throughout the northern temperate regions of the globe.

The flowers are usually white to pink, with five petals and five sepals. They are borne singly, or in umbels of two to six or sometimes more on racemes. The fruit is a drupe (a "prune") with a relatively large hard coated seed (a "stone"). Leaves are simple and usually lanceolate, unlobed and toothed along the margin.

Etymology

The Online Etymology Dictionary presents the customary derivations of plum^[2] and prune^[3] from Latin prūnum,^[4] the plum fruit. The tree is prūnus;^[5] however, Pliny also uses prūnus silvestris to mean the blackthorn. The word is not native Latin, but is a loan from Greek προῦνον (prounon) which is a variant of προῦμνον (proumnon),^[6] origin unknown. The tree is προύμνη (proumnē).^[7] Most dictionaries follow Hoffman, Etymologisches Wörterbuch des Grieschischen, in making some form of the word a loan from a pre-Greek language of Asia Minor, related to Phrygian.

The first use of Prunus as a genus name was by Linnaeus in Hortus Cliffortianus of 1737, which went on to become Species Plantarum. In that work Linnaeus attributes the word to "Varr.", who it is assumed must be Marcus Terentius Varro.

Classification

Linnean classification

In 1737 Linnaeus used four genera to include the species of modern Prunus — Amygdalus, Cerasus, Prunus and Padus — but simplified it to Amygdalus and Prunus in 1758.^[8] Since then the various genera of Linnaeus and others have become subgenera and sections, as it is clearer that all the species are more closely related. Liberty Hyde Bailey says:^[9]

"The numerous forms grade into each other so imperceptibly and inextricably that the genus cannot be readily broken up into species."

Modern classification

A recent DNA study of 48 species concluded that Prunus is monophyletic and is descended from some Eurasian ancestor.^[10]

Historical treatments break the genus up into several different genera, but this segregation is not currently widely recognised other than at the subgeneric rank. ITIS recognises just the single genus Prunus, with an open list of species,^[11] all of which are shown below, under "Species".^[12]

One standard modern treatment of the subgenera derives from the work of Alfred Rehder in 1940. Rehder hypothesized five subgenera: Amygdalus, Prunus, Cerasus, Padus and Laurocerasus.^[13] To them C. Ingram added Lithocerasus.^[14] The six subgenera are described as follows:

• Prunus subgenera:
  • Subgenus Amygdalus: almonds and peaches. Axillary buds in threes (vegetative bud central, two flower buds to sides). Flowers in early spring, sessile or nearly so, not on leafed shoots. Fruit with a groove along one side; stone deeply grooved. Type species Prunus dulcis (Almond).
  • Subgenus Prunus: plums and apricots. Axillary buds solitary. Flowers in early spring stalked, not on leafed shoots. Fruit with a groove along one side; stone rough. Type species Prunus domestica (Plum).
  • Subgenus Cerasus: cherries. Axillary buds single. Flowers in early spring in corymbs, long-stalked, not on leafed shoots. Fruit not grooved; stone smooth. Type species Prunus cerasus (Sour cherry).
  • Subgenus Lithocerasus. Axillary buds in threes. Flowers in early spring in corymbs, long-stalked, not on leafed shoots. Fruit not grooved; stone smooth. Type species Prunus pumila (Sand cherry).
  • Subgenus Padus: bird cherries. Axillary buds single. Flowers in late spring in racemes on leafy shoots, short-stalked. Fruit not grooved; stone smooth. Type species Prunus padus (European bird cherry).
  • Subgenus Laurocerasus: cherry-laurels. Axillary buds single. Flowers in early spring in racemes, not on leafed shoots, short-stalked. Fruit not grooved; stone smooth. Mostly evergreen (all the other subgenera are deciduous). Type species Prunus laurocerasus (European cherry-laurel).

Another recent DNA study^[13] found that Amygdaloideae can be divided into two clades: Prunus-Maddenia, with Maddenia basal within Prunus, and Exochorda-Oemleria-Prinsepia, but further refinement^[1] shows that Exochorda-Oemleria-Prinsepia is somewhat separate from Prunus-Maddenia-Pygeum, and that, like subfamily Maloideae, all of these genera appear to be best considered within subfamily Spiraeoideae. Prunus can be divided into two clades: Amygdalus-Prunus and Cerasus-Laurocerasus-Padus. Yet another study adds Emplectocladus as a subgenus to the former.^[15]

Uses

Japanese Cherry (Prunus serrulata) in bloom

Cherries are prone to gummosis

The genus Prunus includes the almond, apricot, cherry, peach and plum, all of which have cultivars developed for commercial fruit and "nut" production. The edible part of the almond is the seed; the almond fruit is a drupe and not a true nut. Many other species are occasionally cultivated or used for their seed and fruit.

There are also a number of species, hybrids, and cultivars grown as ornamental plants, usually for their profusion of flowers, sometimes for ornamental foliage and shape, occasionally for their bark. These ornamentals include the group that may be collectively called flowering cherries (including sakura, the Japanese flowering cherries).

Other species such as blackthorn are grown for hedging, game cover, and other utilitarian purposes.

The wood of some species is a minor and specialised timber (cherry wood), usually from larger tree species such as the wild cherry.

Many species produce an aromatic resin from wounds in the trunk; this is sometimes used medicinally. There are other minor uses, including other medicinal uses, and dye production.

Pygeum is a herbal remedy containing extracts from the bark of Prunus africana. It is used as to alleviate some of the discomfort caused by inflammation in patients suffering from benign prostatic hyperplasia.

Because of their considerable value as both food and ornamental plants, many Prunus species have been introduced to parts of the world to which they are not native, some becoming naturalised.

Prunus species are food plants for the larvae of a large number of Lepidoptera species (butterflies and moths); see List of Lepidoptera which feed on Prunus.

Toxicity

Many species are cyanogenic; that is, they contain compounds called cyanogenic glucosides, notably amygdalin, which, on hydrolysis, yield hydrogen cyanide (HCN).^[16] Although the fruits of some may be edible by humans and livestock (in addition to the ubiquitous fructivory of birds), seeds, leaves and other parts may be toxic, some highly.^[17] The plants contain no more than trace amounts of HCN but on decomposition after crushing and exposure to air or on digestion poisonous amounts may be generated. The trace amounts may give a characteristic taste ("bitter almond") with increasing bitterness in larger quantities, less tolerable to people than to birds, which habitually feed on specific fruits.

Species

Old World

New World

Palaeobotanical models

The development sequence of a nectarine (Prunus persica) over a 7½ month period, from bud formation in early winter to fruit ripening in midsummer.

The earliest known fossil Prunus are wood, drupe and seed and a leaf from the middle Eocene of the Princeton Chert of British Columbia.^[18] Using the known age as calibration data, recent research by Oh and Potter^[19] reconstructs a partial phylogeny of some Rosaceae from a number of nucleotide sequences. According to this study Prunus and its "sister clade" Maloideae (apple subfamily) diverged at 44.3 mya (or 43 million years ago, well before most of the Primates existed). This date is within the Lutetian, or older middle Eocene.^[20] Stokey and Wehr report:^[18] "The Eocene was a time of rapid evolution and diversification in Angiosperm families such as the Rosaceae ...."

The Princeton finds are among a large number of Angiosperm fossils from the Okanagan Highlands dating to the late early and middle Eocene. Crataegus is found at three locations: Mcabee, Republic and Princeton, while Prunus is found at those locations and Quilchena and Chuchua. A recent recapitulation of research on the topic^[21] reports that the Rosaceae were more diverse at higher altitudes. The Okanagan formations date to as early as 52 mya, but the 44.3 mya data, which is approximate, depending on assumptions, might still apply. The authors state: "... the McAbee flora records a diverse early middle Eocene angiosperm-dominated forest."^[22]

Notes

Bibliography

• Dillhoff, Richard M; Leopold, Estella B.; Manchester, Steven R. (February 2005). "The McAbee flora of British Columbia and its relation to the Early-Middle Eocene Okanagan Highlands flora of the Pacific Northwest" (PDF). Canadian Journal of Earth Sciences 42 (2): 151. doi:10.1139/e04-084. http://www.evolvingearth.org/learnearthscience/mcabeefeb2005cjes.pdf. 
• Stockey, Ruth A.; Wehr, Wesley C. (1996). "Flowering Plants in and around Eocene Lakes of the Interior". In Ludvigson, Rolf. Life in Stone: a Natural History of British Columbia's Fossils. Vancouver: UBCPess. ISBN 0-7748-0578-1 .

External links

• "GRIN Species Records of Prunus". Beltsville, Maryland: USDA, ARS, National Genetic Resources Program. Germplasm Resources Information Network - (GRIN) [Online Database]. National Germplasm Resources Laboratory. http://www.ars-grin.gov/cgi-bin/npgs/html/splist.pl?9887. Retrieved 13 November 2009. 
• "Our Cherries Collection — Prunus". Missouri Botanical Garden: Kemper Center for Home Gardening. 2001-2009. http://www.mobot.org/gardeninghelp/plantcollection.asp?code=4. Retrieved 13 November 2009.