Prunus is a genus of trees and shrubs, which includes the plums, cherries, peaches, nectarines, apricots and almonds. Around 430 species are spread throughout the northern temperate regions of the globe. Many members of the genus are widely cultivated for fruit and ornament. The fruit from this genus are commonly called the stone fruit.
Members of the genus can be deciduous or evergreen. A few species have spiny stems. The leaves are simple, alternate, usually lanceolate, unlobed, and often with nectaries on the leaf stalk. The flowers are usually white to pink, sometimes red, with five petals and five sepals. There are numerous stamens. Flowers are borne singly, or in umbels of two to six or sometimes more on racemes. The fruit is a fleshy drupe (a "prune") with a single relatively large, hard-coated seed (a "stone").
Within the rose family Rosaceae, it was traditionally placed as a subfamily, the Amygdaloideae (incorrectly "Prunoideae"), but was sometimes placed in its own family, the Prunaceae (or Amygdalaceae). More recently, it has become apparent that Prunus evolved from within a much larger clade now called subfamily Amygdaloideae (incorrectly "Spiraeoideae").
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. 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:
- "The numerous forms grade into each other so imperceptibly and inextricably that the genus cannot be readily broken up into species."
Historical treatments break the genus 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, all of which are shown below, under "Species".
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. To them C. Ingram added Lithocerasus. 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: mostly evergreen (all the other subgenera are deciduous); axillary buds single; flowers in early spring in racemes, not on leafed shoots, short-stalked; fruit not grooved, stone smooth; type species: Prunus laurocerasus (European cherry-laurel)
Another recent DNA study found that there are two clades: Prunus-Maddenia, with Maddenia basal within Prunus, and Exochorda-Oemleria-Prinsepia, but further refinement shows that Exochorda-Oemleria-Prinsepia is somewhat separate from Prunus-Maddenia-Pygeum, and that, like the traditional subfamily Maloideae with apple-like fruits, all of these genera appear to be best considered within the expanded subfamily Amygdaloideae. Prunus can be divided into two clades: Amygdalus-Prunus and Cerasus-Laurocerasus-Padus. Yet another study adds Emplectocladus as a subgenus to the former.
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, not a true nut. Many other species are occasionally cultivated or used for their seed and fruit.
A number of species, hybrids, and cultivars are also grown as ornamental plants, usually for their profusion of flowers, sometimes for ornamental foliage and shape, and 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 (Prunus spinosa), are grown for hedging, game cover, and other utilitarian purposes.
The wood of some species (notably cherry) is a specialised timber.
Many species produce an aromatic resin from wounds in the trunk; this is sometimes used medicinally. Other minor uses include dye production.
Pygeum, a herbal remedy containing extracts from the bark of Prunus africana, is used as to alleviate some of the discomfort caused by inflammation in patients suffering from benign prostatic hyperplasia.
Many species are cyanogenic; that is, they contain compounds called cyanogenic glucosides, notably amygdalin, which, on hydrolysis, yield hydrogen cyanide. 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 so. The plants contain no more than trace amounts of hydrogen cyanide, 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.
Pests and diseases
Various Prunus species are winter hosts of the Damson-hop aphid, Phorodon humuli, which is destructive to hops Humulus lupulus just at the time of their maturity, so it is recommended that plum trees not be grown in the vicinity of hop fields.
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The lists below are incomplete, but include most of the better known species.
The earliest known fossil Prunus specimens are wood, drupe and seed and a leaf from the middle Eocene of the Princeton Chert of British Columbia. Using the known age as calibration data, recent research by Oh and Potter 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. Stokey and Wehr report: "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 reported that the Rosaceae were more diverse at higher altitudes. The Okanagan formations date to as early as 52 mya, but the 44.3 mya date, which is approximate, depending on assumptions, might still apply. The authors state: "... the McAbee flora records a diverse early middle Eocene angiosperm-dominated forest."
The Online Etymology Dictionary presents the customary derivations of plum and prune from Latin prūnum, the plum fruit. The tree is prūnus; and Pliny 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), origin unknown. The tree is προύμνη (proumnē). Most dictionaries follow Hoffman, Etymologisches Wörterbuch des Griechischen, 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.
- Potter, D.; Eriksson, T.; Evans, R.C.; Oh, S.; Smedmark, J.E.E.; Morgan, D.R.; Kerr, M.; Robertson, K.R.; Arsenault, M.; Dickinson, T.A.; Campbell, C.S. (2007). "Phylogeny and classification of Rosaceae". Plant Systematics and Evolution 266 (1–2): 5–43. doi:10.1007/s00606-007-0539-9. http://rd.springer.com/journal/606/266/1/page/1#page-1. [Referring to the subfamily by the name "Spiraeoideae"]
- European Garden Flora; vol. 4
- Linnaeus Carolus; Sprengel, Curtius (editor) (1830). Genera Plantarum Editio Nona (Genera plantarum, ninth edition). Gottingen: Dieterich page 402 for Amygdalus, page 403 for Prunus..
- Bailey, Liberty Hyde (1898). Sketch of the Evolution of Our Native Fruits. New York: The MacMillan Company. p. 181.
- Bortiri, Esteban; and others, E.; Oh, S. H.; Jiang, J.; Baggett, S.; Granger, A.; Weeks, C.; Buckingham, M.; Potter, D. et al. (2001). "Phylogeny and Systematics of Prunus (Rosaceae) as Determined by Sequence Analysis of ITS and the Chloroplast trnL-trnF Spacer DNA". Systematic Botany 26 (4): 797–807. JSTOR 3093861 . Abstract and first page for free.
- Do a search in the ITIS database on the scientific name Prunus for its current list.
- Other established species appear as well, which for whatever reasons are not yet in ITIS.
- Lee, Sangtae; Wen, Jun (2001). "A phylogenetic analysis of Prunus and the Amygdaloideae (Rosaceae) using ITS sequences of nuclear ribosomal DNA". American Journal of Botany 88 (1): 150–160. doi:10.2307/2657135. JSTOR 2657135. PMID 11159135. http://www.amjbot.org/cgi/content/full/88/1/150?ck=nck#T1.
- Okie, William (July 2003). "Stone Fruits". Encyclopedia of Fruits and Nuts.
- Bortiri, Esteban; Oh, Sang-Hun; Gao, Fang-You; Potter, Dan (2002). "The phylogenetic utility of nucleotide sequences of sorbitol 6-phosphate dehydrogenase in Prunus (Rosaceae)" (PDF). American Journal of Botany 89 (11): 1697–1708. doi:10.3732/ajb.89.10.1697. http://www.amjbot.org/cgi/reprint/89/10/1697.pdf. The specification is Emplectocladus (Torr.) Sargent
- Armstrong, E. Frankland (1913). "Glucosides". In Davis, W.A.; Sadtler, Samuel S.. Allen's Commercial Organic Analysis, etc. (Fourth ed.). Philadelphia: P. Blakiston's Son & Co.. p. 102. "Amygdalin ... is found in bitter almonds and in the kernels of peaches, cherries, plums, apples, etc. It is hydrolysed by emulsin to hydrogen cyanide, usually in their leaves and seeds"
- Cook, Laurence Martin; Callow, Robert S. (1999). Genetic and evolutionary diversity: the sport of nature (2nd ed.). Cheltenham: Stanley Thornes. p. 135.
- Rothamstead Insect Survey, Rothamstead Research (undated). "Damson-hop aphid, Phorodon humuli". http://www.rothamsted.ac.uk/insect-survey/STPhorodon_humuli.php.
- Day, Kevin (1999-01-27). "Peach and Nectarine Cork Spot:A Review of the 1998 Season". University of California, Davis. http://cetulare.ucdavis.edu/pubfruit/peach.htm. Retrieved 2010-04-01.
- Stockey & Wehr, pp 234, 241, 245.
- Oh, Sang-Hun; Potter, Daniel (2005). "Molecular phylogenetic systematics and biogeography of tribe Neillieae (Rosaceae) using DNA sequences of cpDNA, rDNA, and LEAFY1". American Journal of Botany 92 (1): 179–192. doi:10.3732/ajb.92.1.179. PMID 21652396. http://www.amjbot.org/cgi/content/full/92/1/179.
- A date of 76 mya is given for Rosaceae, which is within the late Cretaceous.
- Dillhoff & Leopold (2005), pp 151–166
- Dillhoff & Leopold (2005), p 165.
- "plum". Online Etymological Dictionary. http://www.etymonline.com/index.php?term=plum.
- "prune". Online Etymological Dictionary. http://www.etymonline.com/index.php?term=prune.
- "prūnum". Lewis's Elementary Latin Dictionary. Perseus Digital Library. 1890. http://artfl.uchicago.edu/cgi-bin/philologic/getobject.pl?c.6:1:2066.latinsmall.
- "prūnus". Lewis's Elementary Latin Dictionary. Perseus Digital Library. 1890. http://artfl.uchicago.edu/cgi-bin/philologic/getobject.pl?c.6:1:2067.latinsmall.
- "προῦμνον". Liddell and Scott's Greek-English Lexicon. Perseus Digital Library. http://artfl.uchicago.edu/cgi-bin/philologic/getobject.pl?c.59:3:144.lsj.
- "προύμνη". Liddell and Scott's Greek-English Lexicon. Perseus Digital Library. http://artfl.uchicago.edu/cgi-bin/philologic/getobject.pl?c.59:3:143.lsj.
- 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 .