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87-439: About 30 species; see text Pears are fruits produced and consumed around the world, growing on a tree and harvested in late summer into mid-autumn. The pear tree and shrub are a species of genus Pyrus / ˈ p aɪ r ə s / , in the family Rosaceae , bearing the pomaceous fruit of the same name. Several species of pears are valued for their edible fruit and juices, while others are cultivated as trees. The tree
174-423: A mutation–selection balance . It is predicted that a viral quasispecies at a low but evolutionarily neutral and highly connected (that is, flat) region in the fitness landscape will outcompete a quasispecies located at a higher but narrower fitness peak in which the surrounding mutants are unfit, "the quasispecies effect" or the "survival of the flattest". There is no suggestion that a viral quasispecies resembles
261-405: A ring species . Also, among organisms that reproduce only asexually , the concept of a reproductive species breaks down, and each clone is potentially a microspecies. Although none of these are entirely satisfactory definitions, and while the concept of species may not be a perfect model of life, it is still a useful tool to scientists and conservationists for studying life on Earth, regardless of
348-400: A "classical" method of determining species, such as with Linnaeus, early in evolutionary theory. However, different phenotypes are not necessarily different species (e.g. a four-winged Drosophila born to a two-winged mother is not a different species). Species named in this manner are called morphospecies . In the 1970s, Robert R. Sokal , Theodore J. Crovello and Peter Sneath proposed
435-424: A 'smallest clade' idea" (a phylogenetic species concept). Mishler and Wilkins and others concur with this approach, even though this would raise difficulties in biological nomenclature. Wilkins cited the ichthyologist Charles Tate Regan 's early 20th century remark that "a species is whatever a suitably qualified biologist chooses to call a species". Wilkins noted that the philosopher Philip Kitcher called this
522-471: A bulbous end. The fruit is a pseudofruit composed of the receptacle or upper end of the flower stalk (the so-called calyx tube) greatly dilated. Enclosed within its cellular flesh is the true fruit: 2–5 ' cartilaginous ' carpels , known colloquially as the "core". Pears and apples cannot always be distinguished by the form of the fruit; some pears look very much like some apples, e.g. the nashi pear . Pear cultivation in temperate climates extends to
609-428: A connected series of neighbouring populations, each of which can sexually interbreed with adjacent related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" population. Such non-breeding, though genetically connected, "end" populations may co-exist in the same region thus closing
696-432: A different species from its ancestors. Viruses have enormous populations, are doubtfully living since they consist of little more than a string of DNA or RNA in a protein coat, and mutate rapidly. All of these factors make conventional species concepts largely inapplicable. A viral quasispecies is a group of genotypes related by similar mutations, competing within a highly mutagenic environment, and hence governed by
783-508: A genetic boundary suitable for defining a species concept is present. DNA barcoding has been proposed as a way to distinguish species suitable even for non-specialists to use. One of the barcodes is a region of mitochondrial DNA within the gene for cytochrome c oxidase . A database, Barcode of Life Data System , contains DNA barcode sequences from over 190,000 species. However, scientists such as Rob DeSalle have expressed concern that classical taxonomy and DNA barcoding, which they consider
870-482: A lesser degree. Other species are used as rootstocks for European and Asian pears and as ornamental trees . Pear wood is close-grained and has been used as a specialized timber for fine furniture and making the blocks for woodcuts . The Manchurian or Ussurian Pear, Pyrus ussuriensis (which produces unpalatable fruit primarily used for canning) has been crossed with Pyrus communis to breed hardier pear cultivars. The Bradford pear ( Pyrus calleryana 'Bradford')
957-492: A misnomer, need to be reconciled, as they delimit species differently. Genetic introgression mediated by endosymbionts and other vectors can further make barcodes ineffective in the identification of species. A phylogenetic or cladistic species is "the smallest aggregation of populations (sexual) or lineages (asexual) diagnosable by a unique combination of character states in comparable individuals (semaphoronts)". The empirical basis – observed character states – provides
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#17327723843411044-507: A moderate amount of dietary fiber , and no micronutrients in significant amounts (table). A 2019 review found preliminary evidence for the potential of pear consumption to favorably affect cardiovascular health. Pears grow in the sublime orchard of Alcinous , in the Odyssey vii: "Therein grow trees, tall and luxuriant, pears and pomegranates and apple -trees with their bright fruit, and sweet figs , and luxuriant olives . Of these
1131-449: A particular species, including which genus (and higher taxa) it is placed in, is a hypothesis about the evolutionary relationships and distinguishability of that group of organisms. As further information comes to hand, the hypothesis may be corroborated or refuted. Sometimes, especially in the past when communication was more difficult, taxonomists working in isolation have given two distinct names to individual organisms later identified as
1218-489: A recipe for a spiced, stewed-pear patina , or soufflé . Romans also introduced the fruit to Britain. Pyrus nivalis , which has white down on the undersurface of the leaves, is chiefly used in Europe in the manufacture of perry (see also cider ). Other small-fruited pears, distinguished by their early ripening and globose fruit, may be referred to as P. cordata , a species found wild in southwestern Europe. The genus
1305-400: A short way of saying that something applies to many species within a genus, but not to all. If scientists mean that something applies to all species within a genus, they use the genus name without the specific name or epithet. The names of genera and species are usually printed in italics . However, abbreviations such as "sp." should not be italicised. When a species' identity is not clear,
1392-404: A specialist may use "cf." before the epithet to indicate that confirmation is required. The abbreviations "nr." (near) or "aff." (affine) may be used when the identity is unclear but when the species appears to be similar to the species mentioned after. With the rise of online databases, codes have been devised to provide identifiers for species that are already defined, including: The naming of
1479-523: A species as groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups. It has been argued that this definition is a natural consequence of the effect of sexual reproduction on the dynamics of natural selection. Mayr's use of the adjective "potentially" has been a point of debate; some interpretations exclude unusual or artificial matings that occur only in captivity, or that involve animals capable of mating but that do not normally do so in
1566-400: A species as determined by a taxonomist. A typological species is a group of organisms in which individuals conform to certain fixed properties (a type), so that even pre-literate people often recognise the same taxon as do modern taxonomists. The clusters of variations or phenotypes within specimens (such as longer or shorter tails) would differentiate the species. This method was used as
1653-491: A species. All species definitions assume that an organism acquires its genes from one or two parents very like the "daughter" organism, but that is not what happens in HGT. There is strong evidence of HGT between very dissimilar groups of prokaryotes , and at least occasionally between dissimilar groups of eukaryotes , including some crustaceans and echinoderms . The evolutionary biologist James Mallet concludes that there
1740-685: A species. Generally the term includes the unknown element of a distinct act of creation. Many authors have argued that a simple textbook definition, following Mayr's concept, works well for most multi-celled organisms , but breaks down in several situations: Species identification is made difficult by discordance between molecular and morphological investigations; these can be categorised as two types: (i) one morphology, multiple lineages (e.g. morphological convergence , cryptic species ) and (ii) one lineage, multiple morphologies (e.g. phenotypic plasticity , multiple life-cycle stages). In addition, horizontal gene transfer (HGT) makes it difficult to define
1827-528: A taxonomic decision at the discretion of cognizant specialists, is not governed by the Codes of Zoological or Botanical Nomenclature, in contrast to the PhyloCode , and contrary to what is done in several other fields, in which the definitions of technical terms, like geochronological units and geopolitical entities, are explicitly delimited. The nomenclatural codes that guide the naming of species, including
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#17327723843411914-517: A traditional biological species. The International Committee on Taxonomy of Viruses has since 1962 developed a universal taxonomic scheme for viruses; this has stabilised viral taxonomy. Most modern textbooks make use of Ernst Mayr 's 1942 definition, known as the Biological Species Concept as a basis for further discussion on the definition of species. It is also called a reproductive or isolation concept. This defines
2001-447: A variation on the morphological species concept, a phenetic species, defined as a set of organisms with a similar phenotype to each other, but a different phenotype from other sets of organisms. It differs from the morphological species concept in including a numerical measure of distance or similarity to cluster entities based on multivariate comparisons of a reasonably large number of phenotypic traits. A mate-recognition species
2088-515: A variety of reasons. Viruses are a special case, driven by a balance of mutation and selection , and can be treated as quasispecies . Biologists and taxonomists have made many attempts to define species, beginning from morphology and moving towards genetics . Early taxonomists such as Linnaeus had no option but to describe what they saw: this was later formalised as the typological or morphological species concept. Ernst Mayr emphasised reproductive isolation, but this, like other species concepts,
2175-438: Is "an entity composed of organisms which maintains its identity from other such entities through time and over space, and which has its own independent evolutionary fate and historical tendencies". This differs from the biological species concept in embodying persistence over time. Wiley and Mayden stated that they see the evolutionary species concept as "identical" to Willi Hennig 's species-as-lineages concept, and asserted that
2262-400: Is a group of sexually reproducing organisms that recognise one another as potential mates. Expanding on this to allow for post-mating isolation, a cohesion species is the most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms; no matter whether populations can hybridise successfully, they are still distinct cohesion species if
2349-458: Is a set of organisms adapted to a particular set of resources, called a niche, in the environment. According to this concept, populations form the discrete phenetic clusters that we recognise as species because the ecological and evolutionary processes controlling how resources are divided up tend to produce those clusters. A genetic species as defined by Robert Baker and Robert Bradley is a set of genetically isolated interbreeding populations. This
2436-562: Is accelerated by the gas ethylene . If pears are placed next to bananas in a fruit bowl, the ethylene emitted by the banana causes the pears to ripen. Refrigeration will slow further ripening. According to Pear Bureau Northwest, most varieties show little color change as they ripen (though the skin on Bartlett pears changes from green to yellow as they ripen). Pears are consumed fresh, canned, as juice , and dried . The juice can also be used in jellies and jams , usually in combination with other fruits, including berries. Fermented pear juice
2523-414: Is between 8 and 8.7 million. About 14% of these had been described by 2011. All species (except viruses ) are given a two-part name , called a "binomial". The first part of a binomial is the genus to which the species belongs. The second part is called the specific name or the specific epithet (in botanical nomenclature , also sometimes in zoological nomenclature ). For example, Boa constrictor
2610-566: Is called perry or pear cider and is made in a way that is similar to how cider is made from apples. Perry can be distilled to produce an eau de vie de poire , a colorless, unsweetened fruit brandy. Pear purée is used to manufacture snack foods such as Fruit by the Foot and Fruit Roll-Ups . The culinary or cooking pear is green but dry and hard, and only edible after several hours of cooking. Two Dutch cultivars are Gieser Wildeman (a sweet variety) and Saint Remy (slightly sour). Pear wood
2697-414: Is called speciation . Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book The Origin of Species . Speciation depends on a measure of reproductive isolation , a reduced gene flow. This occurs most easily in allopatric speciation, where populations are separated geographically and can diverge gradually as mutations accumulate. Reproductive isolation
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2784-403: Is described formally, in a publication that assigns it a unique scientific name. The description typically provides means for identifying the new species, which may not be based solely on morphology (see cryptic species ), differentiating it from other previously described and related or confusable species and provides a validly published name (in botany) or an available name (in zoology) when
2871-671: Is further weakened by the existence of microspecies , groups of organisms, including many plants, with very little genetic variability, usually forming species aggregates . For example, the dandelion Taraxacum officinale and the blackberry Rubus fruticosus are aggregates with many microspecies—perhaps 400 in the case of the blackberry and over 200 in the dandelion, complicated by hybridisation , apomixis and polyploidy , making gene flow between populations difficult to determine, and their taxonomy debatable. Species complexes occur in insects such as Heliconius butterflies, vertebrates such as Hypsiboas treefrogs, and fungi such as
2958-726: Is hard or even impossible to test. Later biologists have tried to refine Mayr's definition with the recognition and cohesion concepts, among others. Many of the concepts are quite similar or overlap, so they are not easy to count: the biologist R. L. Mayden recorded about 24 concepts, and the philosopher of science John Wilkins counted 26. Wilkins further grouped the species concepts into seven basic kinds of concepts: (1) agamospecies for asexual organisms (2) biospecies for reproductively isolated sexual organisms (3) ecospecies based on ecological niches (4) evolutionary species based on lineage (5) genetic species based on gene pool (6) morphospecies based on form or phenotype and (7) taxonomic species,
3045-529: Is known about his biography is gleaned from his book. It appears that he was a large landowner whose interests lay exclusively with agricultural matters. It is clear that he did much hands-on growing and experimenting with a wide range of crops himself. It is also clear that he was well-read in the agricultural writings of his predecessors. The work is mostly compiled from the writings of other authors. Al-'Awwam cites information from 112 different prior authors. His citations of earlier authors have been analyzed with
3132-420: Is medium-sized and native to coastal and mildly temperate regions of Europe, North Africa, and Asia. Pear wood is one of the preferred materials in the manufacture of high-quality woodwind instruments and furniture . About 3,000 known varieties of pears are grown worldwide, which vary in both shape and taste. The fruit is consumed fresh, canned , as juice , dried , or fermented as perry . The word pear
3219-403: Is no easy way to tell whether related geographic or temporal forms belong to the same or different species. Species gaps can be verified only locally and at a point of time. One is forced to admit that Darwin's insight is correct: any local reality or integrity of species is greatly reduced over large geographic ranges and time periods. The botanist Brent Mishler argued that the species concept
3306-478: Is not valid, notably because gene flux decreases gradually rather than in discrete steps, which hampers objective delimitation of species. Indeed, complex and unstable patterns of gene flux have been observed in cichlid teleosts of the East African Great Lakes . Wilkins argued that "if we were being true to evolution and the consequent phylogenetic approach to taxa, we should replace it with
3393-745: Is one of the preferred materials in the manufacture of high-quality woodwind instruments and furniture , and was used for making the carved blocks for woodcuts . It is also used for wood carving, and as a firewood to produce aromatic smoke for smoking meat or tobacco . Pear wood is valued for kitchen spoons, scoops and stirrers, as it does not contaminate food with color, flavor or smell, and resists warping and splintering despite repeated soaking and drying cycles. Lincoln describes it as "a fairly tough, very stable wood... (used for) carving... brushbacks, umbrella handles, measuring instruments such as set squares and T-squares... recorders... violin and guitar fingerboards and piano keys... decorative veneering." Pearwood
3480-400: Is one of the species of the genus Boa , with constrictor being the species' epithet. While the definitions given above may seem adequate at first glance, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation , in a species complex of hundreds of similar microspecies , and in
3567-457: Is probably from Germanic pera as a loanword of Vulgar Latin pira , the plural of pirum , akin to Greek apios (from Mycenaean ápisos ), of Semitic origin ( pirâ ), meaning "fruit". The adjective pyriform or piriform means pear-shaped. The classical Latin word for a pear tree is pirus ; pyrus is an alternate form of this word sometimes used in medieval Latin . The pear is native to coastal, temperate, and mountainous regions of
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3654-586: Is similar to Mayr's Biological Species Concept, but stresses genetic rather than reproductive isolation. In the 21st century, a genetic species could be established by comparing DNA sequences. Earlier, other methods were available, such as comparing karyotypes (sets of chromosomes ) and allozymes ( enzyme variants). An evolutionarily significant unit (ESU) or "wildlife species" is a population of organisms considered distinct for purposes of conservation. In palaeontology , with only comparative anatomy (morphology) and histology from fossils as evidence,
3741-496: Is sometimes an important source of genetic variation. Viruses can transfer genes between species. Bacteria can exchange plasmids with bacteria of other species, including some apparently distantly related ones in different phylogenetic domains , making analysis of their relationships difficult, and weakening the concept of a bacterial species. Ibn al-%27Awwam Ibn al-'Awwam ( Arabic : ابن العوام ), also called Abu Zakariya Ibn al-Awwam ( Arabic : أبو زكريا بن العوام ),
3828-434: Is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity . Other ways of defining species include their karyotype , DNA sequence, morphology , behaviour, or ecological niche . In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. The most recent rigorous estimate for the total number of species of eukaryotes
3915-423: Is the favored wood for architect's rulers because it does not warp. It is similar to the wood of its relative, the apple tree ( Malus domestica ) and used for many of the same purposes. Raw pear is 84% water, 15% carbohydrates and contains negligible protein and fat (table). In a 100 g ( 3 + 1 ⁄ 2 oz) reference amount, raw pear supplies 239 kilojoules (57 kilocalories) of food energy ,
4002-614: Is thought to have originated in present-day Western China in the foothills of the Tian Shan , a mountain range of Central Asia, and to have spread to the north and south along mountain chains, evolving into a diverse group of over 20 widely recognized primary species. The enormous number of varieties of the cultivated European pear ( Pyrus communis subsp. communis ), are likely derived from one or two wild subspecies ( P. c. subsp. pyraster and P. c. subsp. caucasica ), widely distributed throughout Europe, and sometimes forming part of
4089-594: Is threatened by hybridisation, but this can be selected against once a pair of populations have incompatible alleles of the same gene, as described in the Bateson–Dobzhansky–Muller model . A different mechanism, phyletic speciation, involves one lineage gradually changing over time into a new and distinct form (a chronospecies ), without increasing the number of resultant species. Horizontal gene transfer between organisms of different species, either through hybridisation , antigenic shift , or reassortment ,
4176-656: Is widespread as an ornamental tree in North America, where it has become invasive in regions. It is also used as a blight-resistant rootstock for Pyrus communis fruit orchards. The Willow-leaved pear ( Pyrus salicifolia ) is grown for its silvery leaves, flowers, and its "weeping" form. The following cultivars have gained the Royal Horticultural Society 's Award of Garden Merit : The purely decorative cultivar P. salicifolia 'Pendula', with pendulous branches and silvery leaves, has also won
4263-830: The Celtic languages , while in Slavic and other dialects, differing appellations still referring to the same thing are found—a diversity and multiplicity of nomenclature , which led Alphonse Pyramus de Candolle to infer a very ancient cultivation of the tree from the shores of the Caspian to those of the Atlantic. The pear was also cultivated by the Romans, who ate the fruits raw or cooked, just like apples. Pliny's Natural History recommended stewing them with honey and noted three dozen varieties. The Roman cookbook De re coquinaria has
4350-665: The Geoponica and the Nabataean Agriculture . Ibn al-Awwam's book is divided into thirty-four chapters. The first thirty deal with crops and the last four deal with livestock. The first four chapters in the book deal successively with different types of soils , fertilizers , irrigation , and planning a garden layout. Then there are five chapters on growing fruit trees, including grafting, pruning, growing from cuttings, etc., and dozens of different fruit trees are treated individually. Later chapters deal with ploughing ,
4437-530: The ICZN for animals and the ICN for plants, do not make rules for defining the boundaries of the species. Research can change the boundaries, also known as circumscription, based on new evidence. Species may then need to be distinguished by the boundary definitions used, and in such cases the names may be qualified with sensu stricto ("in the narrow sense") to denote usage in the exact meaning given by an author such as
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#17327723843414524-1079: The Old World , from Western Europe and North Africa east across Asia. They are medium-sized trees, reaching up to 20 m tall, often with a tall, narrow crown; a few pear species are shrubby . The leaves are alternately arranged, simple, 2–12 cm (1– 4 + 1 ⁄ 2 in) long, glossy green on some species, densely silvery-hairy in some others; leaf shape varies from broad oval to narrow lanceolate. Most pears are deciduous , but one or two species in Southeast Asia are evergreen . Some pears are cold-hardy, withstanding temperatures as low as −25 to −40 °C (−13 to −40 °F) in winter, but many grown for agriculture are vulnerable to cold damage. Evergreen species only tolerate temperatures down to about −12 °C (10 °F). The flowers are white, rarely tinted yellow or pink, 2–4 centimetres (1– 1 + 1 ⁄ 2 in) diameter, and have five petals , five sepals , and numerous stamens . Like that of
4611-399: The fly agaric . Natural hybridisation presents a challenge to the concept of a reproductively isolated species, as fertile hybrids permit gene flow between two populations. For example, the carrion crow Corvus corone and the hooded crow Corvus cornix appear and are classified as separate species, yet they can hybridise where their geographical ranges overlap. A ring species is
4698-507: The jaguar ( Panthera onca ) of Latin America or the leopard ( Panthera pardus ) of Africa and Asia. In contrast, the scientific names of species are chosen to be unique and universal (except for some inter-code homonyms ); they are in two parts used together : the genus as in Puma , and the specific epithet as in concolor . A species is given a taxonomic name when a type specimen
4785-406: The "cynical species concept", and arguing that far from being cynical, it usefully leads to an empirical taxonomy for any given group, based on taxonomists' experience. Other biologists have gone further and argued that we should abandon species entirely, and refer to the "Least Inclusive Taxonomic Units" (LITUs), a view that would be coherent with current evolutionary theory. The species concept
4872-405: The abbreviation "sp." in the singular or "spp." (standing for species pluralis , Latin for "multiple species") in the plural in place of the specific name or epithet (e.g. Canis sp.). This commonly occurs when authors are confident that some individuals belong to a particular genus but are not sure to which exact species they belong, as is common in paleontology . Authors may also use "spp." as
4959-570: The amount of hybridisation is insufficient to completely mix their respective gene pools . A further development of the recognition concept is provided by the biosemiotic concept of species. In microbiology , genes can move freely even between distantly related bacteria, possibly extending to the whole bacterial domain. As a rule of thumb, microbiologists have assumed that members of Bacteria or Archaea with 16S ribosomal RNA gene sequences more similar than 97% to each other need to be checked by DNA–DNA hybridisation to decide if they belong to
5046-404: The award. Summer and autumn cultivars of Pyrus communis , being climacteric fruits , are gathered before they are fully ripe, while they are still green, but snap off when lifted. Certain other pears, including Pyrus pyrifolia and P. × bretschneideri , have both climacteric and non-climacteric varieties. In 2022, world production of pears was 26 million tonnes , led by China with 73% of
5133-588: The best-known of the Vainakh peoples today being the Chechens of Chechnya . Pear and walnut trees were held to be the sacred abodes of beneficent spirits in pre-Islamic Chechen religion and, for this reason, it was forbidden to fell them. Species A species ( pl. : species) is a population of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring , typically by sexual reproduction . It
5220-474: The biological species concept, "the several versions" of the phylogenetic species concept, and the idea that species are of the same kind as higher taxa are not suitable for biodiversity studies (with the intention of estimating the number of species accurately). They further suggested that the concept works for both asexual and sexually-reproducing species. A version of the concept is Kevin de Queiroz 's "General Lineage Concept of Species". An ecological species
5307-505: The biological species concept, a cladistic species does not rely on reproductive isolation – its criteria are independent of processes that are integral in other concepts. Therefore, it applies to asexual lineages. However, it does not always provide clear cut and intuitively satisfying boundaries between taxa, and may require multiple sources of evidence, such as more than one polymorphic locus, to give plausible results. An evolutionary species, suggested by George Gaylord Simpson in 1951,
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#17327723843415394-488: The choice of seeds , the seasons and their tasks, grain farming, leguminous plants, small allotments, aromatic plants and industrial plants. Again, many plants are treated individually on how to cultivate them. One chapter is devoted to methods of preserving and storing foods after harvest, a topic which comes up intermittently elsewhere. The symptoms of many diseases of trees and vines are indicated, as are methods of cure. The chapters on livestock include discussion of
5481-433: The concept of a chronospecies can be applied. During anagenesis (evolution, not necessarily involving branching), some palaeontologists seek to identify a sequence of species, each one derived from the phyletically extinct one before through continuous, slow and more or less uniform change. In such a time sequence, some palaeontologists assess how much change is required for a morphologically distinct form to be considered
5568-460: The cultivated forms. According to Pear Bureau Northwest, about 3,000 known varieties of pears are grown worldwide. The pear is normally propagated by grafting a selected variety onto a rootstock , which may be of a pear or quince variety. Quince rootstocks produce smaller trees, which is often desirable in commercial orchards or domestic gardens. For new varieties the flowers can be cross-bred to preserve or combine desirable traits. The fruit of
5655-482: The diseases and injuries to horses and cattle. Ibn al-Awwam's book, an agriculture encyclopedia of more than a thousand pages, is primarily a compilation of the writings of other authors. But it is a compilation that is guided and informed by Ibn al-Awwam's own rich and non-bookish knowledge of the subject. An edition was published in 1802 with the Arabic text placed alongside a translation into Spanish, and in 1864 it
5742-435: The evidence to support hypotheses about evolutionarily divergent lineages that have maintained their hereditary integrity through time and space. Molecular markers may be used to determine diagnostic genetic differences in the nuclear or mitochondrial DNA of various species. For example, in a study done on fungi , studying the nucleotide characters using cladistic species produced the most accurate results in recognising
5829-533: The following summary results: about 1900 direct and indirect citations altogether, of which 615 are to Greek authors (the great majority to the Geoponica of Cassianus Bassus ), 585 are to Middle Eastern Arabic authors (the great majority to the Book of Nabataean Agriculture attributed to Ibn Wahshiyya ), and 690 are to Andalusian Arabic authors (the great majority to Ibn Bassal , Abu ʾl-Khayr al-Ishbīlī or Ibn Hajjaj, all three of whom wrote books about agriculture in
5916-512: The fruit perishes not nor fails in winter or in summer, but lasts throughout the year." "A Partridge in a Pear Tree" is the first gift in the cumulative song "The Twelve Days of Christmas" . The pear tree was an object of particular veneration (as was the walnut ) in the tree worship of the Nakh peoples of the North Caucasus – see Vainakh mythology and see also Ingushetia –
6003-549: The later 11th century in southern Spain, copies of which have survived only partly and incompletely). Ibn al-Awwam compiled from only a subset of the authors he cites: This subset in turn contains all the material of the full set of authors he cites. His most influential direct sources were the Andalusian Arabic sources, who in turn were acquainted with various non-Andalusian sources, including sources from classical antiquity. Like himself, his Andalusian sources had read
6090-754: The natural vegetation of the forests. Court accounts of Henry III of England record pears shipped from La Rochelle-Normande and presented to the king by the sheriffs of the City of London. The French names of pears grown in English medieval gardens suggest that their reputation, at the least, was French; a favoured variety in the accounts was named for Saint Rieul of Senlis , Bishop of Senlis in northern France. Asian species with medium to large edible fruit include P. pyrifolia , P. ussuriensis , P. × bretschneideri , and P. × sinkiangensis . Small-fruited species, such as Pyrus calleryana , may be used as rootstocks for
6177-483: The numerous fungi species of all the concepts studied. Versions of the phylogenetic species concept that emphasise monophyly or diagnosability may lead to splitting of existing species, for example in Bovidae , by recognising old subspecies as species, despite the fact that there are no reproductive barriers, and populations may intergrade morphologically. Others have called this approach taxonomic inflation , diluting
6264-593: The paper is accepted for publication. The type material is usually held in a permanent repository, often the research collection of a major museum or university, that allows independent verification and the means to compare specimens. Describers of new species are asked to choose names that, in the words of the International Code of Zoological Nomenclature , are "appropriate, compact, euphonious, memorable, and do not cause offence". Books and articles sometimes intentionally do not identify species fully, using
6351-834: The pear is produced on spurs, which appear on shoots more than one year old. There are four species which are primarily grown for edible fruit production: the European pear Pyrus communis subsp. communis cultivated mainly in Europe and North America, the Chinese white pear ( bai li ) Pyrus × bretschneideri , the Chinese pear Pyrus ussuriensis , and the Nashi pear Pyrus pyrifolia (also known as Asian pear or apple pear), which are grown mainly in eastern Asia. There are thousands of cultivars of these three species. A species grown in western China, P. sinkiangensis , and P. pashia , grown in southern China and south Asia, are also produced to
6438-674: The person who named the species, while the antonym sensu lato ("in the broad sense") denotes a wider usage, for instance including other subspecies. Other abbreviations such as "auct." ("author"), and qualifiers such as "non" ("not") may be used to further clarify the sense in which the specified authors delineated or described the species. Species are subject to change, whether by evolving into new species, exchanging genes with other species, merging with other species or by becoming extinct. The evolutionary process by which biological populations of sexually-reproducing organisms evolve to become distinct or reproductively isolated as species
6525-411: The related apple , the pear fruit is a pome , in most wild species 1–4 cm ( 1 ⁄ 2 – 1 + 1 ⁄ 2 in) diameter, but in some cultivated forms up to 18 cm (7 in) long and 9 cm ( 3 + 1 ⁄ 2 in) broad. The shape varies in most species from oblate or globose, to the classic pyriform " pear shape " of the European pear with an elongated basal portion and
6612-563: The remotest antiquity, and evidence exists of its use as a food since prehistoric times. Many traces have been found in prehistoric pile dwellings around Lake Zurich . Pears were cultivated in China as early as 2000 BC. An article on Pear tree cultivation in Spain is brought down in Ibn al-'Awwam 's 12th-century agricultural work, Book on Agriculture . The word pear , or its equivalent, occurs in all
6699-487: The result of misclassification leading to questions on whether there really are any ring species. The commonly used names for kinds of organisms are often ambiguous: "cat" could mean the domestic cat, Felis catus , or the cat family, Felidae . Another problem with common names is that they often vary from place to place, so that puma, cougar, catamount, panther, painter and mountain lion all mean Puma concolor in various parts of America, while "panther" may also mean
6786-586: The ring. Ring species thus present a difficulty for any species concept that relies on reproductive isolation. However, ring species are at best rare. Proposed examples include the herring gull – lesser black-backed gull complex around the North pole, the Ensatina eschscholtzii group of 19 populations of salamanders in America, and the greenish warbler in Asia, but many so-called ring species have turned out to be
6873-508: The same species. This concept was narrowed in 2006 to a similarity of 98.7%. The average nucleotide identity (ANI) method quantifies genetic distance between entire genomes , using regions of about 10,000 base pairs . With enough data from genomes of one genus, algorithms can be used to categorize species, as for Pseudomonas avellanae in 2013, and for all sequenced bacteria and archaea since 2020. Observed ANI values among sequences appear to have an "ANI gap" at 85–95%, suggesting that
6960-529: The same species. When two species names are discovered to apply to the same species, the older species name is given priority and usually retained, and the newer name considered as a junior synonym, a process called synonymy . Dividing a taxon into multiple, often new, taxa is called splitting . Taxonomists are often referred to as "lumpers" or "splitters" by their colleagues, depending on their personal approach to recognising differences or commonalities between organisms. The circumscription of taxa, considered
7047-506: The species concept and making taxonomy unstable. Yet others defend this approach, considering "taxonomic inflation" pejorative and labelling the opposing view as "taxonomic conservatism"; claiming it is politically expedient to split species and recognise smaller populations at the species level, because this means they can more easily be included as endangered in the IUCN red list and can attract conservation legislation and funding. Unlike
7134-624: The subject in any language. It was published in Spanish and French translations in the 19th century. The edition in French is about 1350 pages. His full name was Abu Zakariya Yahya ibn Muhammad ibn Ahmad ibn Al-'Awwam Al-Ishbili ( Arabic : أبو زكريا يحيى بن محمد بن أحمد بن العوام الإشبيلي ). The appellation "Al-Ishbili" at the end of his name means "the Sevillean" i.e. from Seville . His dates of birth and death are known. Nearly everything that
7221-485: The theoretical difficulties. If species were fixed and clearly distinct from one another, there would be no problem, but evolutionary processes cause species to change. This obliges taxonomists to decide, for example, when enough change has occurred to declare that a lineage should be divided into multiple chronospecies , or when populations have diverged to have enough distinct character states to be described as cladistic species. Species and higher taxa were seen from
7308-877: The time of Aristotle until the 18th century as categories that could be arranged in a hierarchy, the great chain of being . In the 19th century, biologists grasped that species could evolve given sufficient time. Charles Darwin 's 1859 book On the Origin of Species explained how species could arise by natural selection . That understanding was greatly extended in the 20th century through genetics and population ecology . Genetic variability arises from mutations and recombination , while organisms themselves are mobile, leading to geographical isolation and genetic drift with varying selection pressures . Genes can sometimes be exchanged between species by horizontal gene transfer ; new species can arise rapidly through hybridisation and polyploidy ; and species may become extinct for
7395-609: The total (table). About 48% of the Southern Hemisphere 's pears are produced in the Patagonian valley of Río Negro in Argentina. Pears may be stored at room temperature until ripe. Pears are ripe when the flesh around the stem gives to gentle pressure. Ripe pears are optimally stored refrigerated, uncovered in a single layer, where they have a shelf life of 2 to 3 days. Pears ripen at room temperature. Ripening
7482-540: The wild. It is difficult to define a species in a way that applies to all organisms. The debate about species concepts is called the species problem. The problem was recognised even in 1859, when Darwin wrote in On the Origin of Species : I was much struck how entirely vague and arbitrary is the distinction between species and varieties. He went on to write: No one definition has satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of
7569-466: Was a Al-Andalus agriculturist who flourished at Seville (modern-day southern Spain ) in the later 12th century. He wrote a lengthy handbook on agriculture entitled in Arabic Kitāb al-Filāḥa ( Arabic : كِتَاب الفِلَاحَة , lit. ''Book on Agriculture''), which is the most comprehensive treatment of the subject in medieval Arabic, and one of the most important medieval works on
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