During 10,000 years of cultivation, numerous forms ofwheat, many of themhybrids, have developed under a combination ofartificial andnatural selection.^[1][2] This diversity has led to much confusion in the naming of wheats. Genetic and morphological characteristics of wheat influence its classification; many common and botanical names of wheat are in current use.

The genusTriticum includes the wild anddomesticated species usually thought of as wheat.

In the 1950s growing awareness of the genetic similarity of the wild goatgrasses (Aegilops) led botanists such as Bowden to amalgamateAegilops andTriticum as one genus,Triticum.^[3] This approach is still followed by some (mainly geneticists), but has not been widely adopted by taxonomists.^[4]Aegilops is morphologically highly distinct fromTriticum, with rounded rather than keeledglumes.^[5]

Aegilops is important in wheatevolution because of its role in two important hybridisation events. Wildemmer (T. dicoccoides andT. araraticum) resulted from thehybridisation of a wild wheat,T. urartu, and an as yet unidentified goatgrass, probably closely related toAe. speltoides.^[7]Hexaploid wheats (e.g.T. aestivum – the most common – andT. spelta) are the result of a hybridisation between a domesticatedtetraploid wheat, probablyT. dicoccum orT. durum, and another goatgrass,Ae. tauschii orAe. squarrosa.^[6][8] The hexaploid genome is anallohexaploid composed of two copies each of three subgenomes, AABBDD.^[9] TheA genome is fromT. urartu (AA).^[9] TheB genome is a descendant of theS genome of an unidentified species related toAegilops sectionSitopsis (SS).^[9] This naturalhybridization event happened ~3–0.8MYA, yielding the tetraploidT. dicoccoides.^[9] In time this tetraploid gave rise toT. turgidum, which gave rise to moderndurum.^[9] Then ~0.4 MYAT. diccocoides naturally crossed withAegilops tauschii (DD), adding theD genome and yielding the hexaploid.^[9]

Botanists of the classical period, such asColumella, and in sixteenth and seventeenth centuryherbals, divided wheats into two groups,Triticum corresponding to free-threshing wheats, andZea corresponding to hulled ('spelt') wheats.^[4]

Carl Linnaeus recognised five species, all domesticated:^[4]

• T. aestivum Bearded spring wheat
• T. hybernum Beardless winter wheat
• T. turgidum Rivet wheat
• T. spelta Spelt wheat
• T. monococcum Einkorn wheat

Later classifications added to the number of species described, but continued to give species status to relatively minor variants, such aswinter- vs.spring- forms. The wild wheats were not described until the mid-19th century because of the poor state of botanical exploration in theNear East, where they grow.^[4]

The development of a modern classification depended on the discovery, in the 1920s, that wheat was divided into 3ploidy levels.^[10]

As with manygrasses,polyploidy is common in wheat.^[11] There are two wild diploid (non-polyploid) wheats,T. boeoticum andT. urartu.T. boeoticum is the wild ancestor of domesticated einkorn,T. monococcum.^[12] Cells of the diploid wheats each contain 2 complements of 7 chromosomes, one from the mother and one from the father (2n=2x=14, where 2n is the number of chromosomes in each somatic cell, and x is the basic chromosome number).

The polyploid wheats aretetraploid (4 sets of chromosomes, 2n=4x=28), orhexaploid (6 sets of chromosomes, 2n=6x=42). The tetraploid wild wheats are wild emmer,T. dicoccoides, andT. araraticum. Wild emmer is the ancestor of all the domesticated tetraploid wheats, with one exception:T. araraticum is the wild ancestor ofT. timopheevii.^[13]

There are no wild hexaploid wheats, although feral forms ofcommon wheat are sometimes found. Hexaploid wheats developed underdomestication. Genetic analysis has shown that the original hexaploid wheats were the result of a cross between a tetraploid domesticated wheat, such asT. dicoccum orT. durum, and a wild goatgrass, such asAe. tauschii.^[8]

Polyploidy is important to wheat classification for three reasons:

• Wheats within one ploidy level will be more closely related to each other.
• Ploidy level influences some plant characteristics. For example, higher levels of ploidy tend to be linked to larger cell size.
• Polyploidy brings newgenomes into a species. For example,Aegilops tauschii brought the D genome into hexaploid wheats, with enhanced cold-hardiness^[14] and some distinctive morphological features.^[15]

Observation of chromosome behaviour duringmeiosis, and the results of hybridisation experiments, have shown thatwheat genomes (complete complements of genetic matter) can be grouped into distinctive types. Each type has been given a name,A,B, andD. Grasses sharing the same genome will be more-or-less interfertile, and might be treated by botanists as one species. Identification of genome types is obviously a valuable tool in investigating hybridisation. For example, if two diploid plants hybridise to form a new polyploid form (an allopolyploid), the two original genomes will be present in the new form. Many thousands of years after the original hybridisation event, identification of the component genomes will allow identification of the original parent species.^[16]

InTriticum, five genomes, all originally found in diploid species, have been identified:

• A^m, also called A^b – present in wild einkorn (T. boeoticum).
• A – present inT. urartu^[9] (closely related toT. boeoticum but not interfertile).
• B – present in most tetraploid wheats. Source not identified, but similar toAe. speltoides.^[9]
• G – present intimopheevii group of wheats. Source not identified, but similar toAe. speltoides.
• D – present inAe. tauschii, and thus in all hexaploid wheats.^[9]

The genetic approach to wheat taxonomy (see below) takes the genome composition as defining each species.^[17] As there are five known combinations inTriticum this translates into fivesuper species:

• A^mT. monococcum
• A^uT. urartu
• BA^uT. turgidum
• GA^mT. timopheevii
• BA^uD,T. aestivum

For a larger list of genome names, seeTriticeae § Genetics.

There are four wild species, all growing in rocky habitats in theFertile Crescent of theNear East.^[18] All the other species aredomesticated. Although relatively few genes control domestication, and wild and domesticated forms are interfertile, wild and domesticated wheats occupy entirely separate habitats. Traditional classification gives more weight to domesticated status.

All wild wheats are hulled: they have tough glumes (husks) that tightly enclose the grains. Eachpackage of glumes, lemma and palaea, and grains is known as a spikelet. At maturity therachis (central stalk of the cereal ear) disarticulates, allowing the spikelets to disperse.^[19]

The first domesticated wheats, einkorn and emmer, were hulled like their wild ancestors, but with rachises that (while not entirely tough) did not disarticulate at maturity. During thePre-Pottery Neolithic B period, at about 8000 BC, free-threshing forms of wheat evolved, with light glumes and fully tough rachis.

Hulled or free-threshing status is important in traditional classification because the different forms are usually grown separately, and have very different post-harvesting processing. Hulled wheats need substantial extra pounding or milling to remove the tough glumes.

In addition to hulled/free-threshing status, other morphological criteria, e.g. spike laxness or glume wingedness, are important in defining wheat forms. Some of these are covered in the individual species accounts linked from this page, butFloras must be consulted for full descriptions and identification keys.

Although the range of recognised types of wheat has been reasonably stable since the 1930s, there are now sharply differing views as to whether these should be recognised at species level (traditional approach) or at subspecific level (genetic approach). The first advocate of the genetic approach was Bowden, in a 1959 classification (now historic rather than current).^[20] He, and subsequent proponents (usually geneticists), argued that forms that were interfertile should be treated as one species (thebiological species concept). Thus emmer and hard wheat should both be treated as subspecies (or at other infraspecific ranks) of a single tetraploid species defined by the genome BA^u. Van Slageren's 1994 classification is probably the most widely used genetic-based classification at present.^[21]

Users of traditional classifications give more weight to the separate habitats of the traditional species, which means that species that could hybridise do not, and to morphological characters. There are also pragmatic arguments for this type of classification: it means that most species can be described in Latin binomials, e.g.Triticum aestivum, rather than the trinomials necessary in the genetic system, e.g.T. a. subsp.aestivum. Both approaches are widely used.

In the nineteenth century, elaborate schemes of classification were developed in which wheat ears were classified to botanicalvariety on the basis of morphological criteria such as glume hairiness and colour or grain colour. These variety names are now largely abandoned, but are still sometimes used for distinctive types of wheat such asmiracle wheat, a form ofT. turgidum with branched ears, known asT. t. L. var.mirabile Körn.

The term "cultivar" (abbreviated ascv.) is often confused with "species" or "domesticate". In fact, it has a precise meaning in botany: it is the term for a distinct population of a crop, usually commercial and resulting from deliberate plant-breeding. Cultivar names are always capitalised, often placed between apostrophes, and not italicised. An example of a cultivar name isT. aestivum cv. 'Pioneer 2163'. A cultivar is often referred to by farmers as a variety, but this is best avoided in print, because of the risk of confusion with botanical varieties. The term "landrace" is applied to informal, farmer-maintained populations of crop plants.

Botanical names for wheat are generally expected to follow an existing classification, such as those listed ascurrent by the Wheat Genetics Resource Center.^[22] The classifications given in the following table are among those suitable for use. If a genetic classification is favoured, the GRIN classification is comprehensive, based on van Slageren's work but with some extra taxa recognised. If the traditional classification is favoured, Dorofeev's work is a comprehensive scheme that meshes well with other less complete treatments. Wikipedia's wheat pages generally follow a version of the Dorofeev scheme – see thetaxobox on the Wheat page.

A general rule is thatdifferent taxonomic schemes should not be mixed in one context. In a given article, book or web page, only one scheme should be used at a time. Otherwise, it will be unclear to others how the botanical name is being used.

Note: Blank common name indicates that no common name is in use in the English language.

• Triticum boeoticumBoiss. is sometimes divided into two subspecies:
  • T. boeoticumBoiss. subsp.thaoudar(Reut. ex Hausskn.) E. Schiem. – with two grains in each spikelet, distributed to east of fertile crescent.
  • T. boeoticumBoiss. subsp.boeoticum – one grain in each spikelet, in Balkans.
• Triticum dicoccumSchrank exSchübler is also known asTriticum dicocconSchrank.
• Triticum aethiopicumJakubz. is a variant form ofT. durum found in Ethiopia. It is not usually regarded as a separate species.
• Triticum karamyscheviiNevsky was previously known asTriticum paleocolchicumA. M. Menabde.

This sectionis missing information about genome and ploidy, if possible. Please expand the section to include this information. Further details may exist on thetalk page.(January 2022)

Russian botanists have given botanical names to hybrids developed during genetic experiments. As these only occur in the laboratory environment, it is questionable whether botanical names (rather than lab. numbers) are justified. Botanical names have also been given to rare mutant forms. Examples include:

• Triticum × borisoviiZhebrak – (T. aestivum ×T. timopheevi)
• Triticum × fungicidumZhuk. – Hexaploid, artificial cross (T. carthlicum ×T. timopheevi)
• Triticum jakubzineriUdachin &Shakhm.
• Triticum militinae Zhuk. &Migush. – mutant form ofT. timopheevi.
• Triticum petropavlovskyi Udachin & Migush.
• Triticum sinskajaeFilat. &Kurkiev – mutant, free-threshing form ofT. monococcum.
• Triticum × timococcum Kostov
• Triticum timonovum Heslot & Ferrary – Hexaploid, artificial cross.
• Triticum zhukovskyiMenabde &Ericzjan (T. timopheevi ×T. monococcum): 6N^[6]

• Winter wheat vs.spring wheat
• Cultivated plant taxonomy
• List of Canadian Heritage Wheat Varieties

• Caligari, P.D.S.; Brandham, P.E., eds. (2001).Wheat taxonomy: the legacy of John Percival(PDF) (Linnean Special Issue 3 ed.). London: Linnean Society. p. 190.
• Percival, John (1921).The wheat plant: a monograph. London: Duckworth.
• Padulosi, Stefano, Karl Hammer and J. Heller (1996).Hulled Wheats. Promoting the conservation and use of underutilized and neglected crops. 4. Proceedings of the First International Workshop on Hulled Wheats 21 July 1995 – 22 July 1995, Castelvecchio Pascoli, Tuscany, Italy. Bioversity International.ISBN 978-92-9043-288-3. Archived fromthe original on January 14, 2006.{{cite book}}: CS1 maint: multiple names: authors list (link)
• "Wheat Classification Tables Site". Archived fromthe original on March 10, 2000. RetrievedJanuary 15, 2006. Lists ofTriticum names. An essential tool.
• "GRIN taxonomy:Triticum". RetrievedJanuary 15, 2006. Includes links to USDA germplasm collection, and public domain imagesGermplasm Resources Information Network (GRIN)
• "Triticum taxonomy".Mansfeld's World Database of Agricultural and Horticultural Crops. RetrievedJanuary 16, 2006.

• Les meilleurs blés (1880 and 1909)Archived February 17, 2006, at theWayback Machine Also onPl@ntUse. Beautifully illustrated French book on wheats then in cultivation and studied by the French breeders family Vilmorin.

• International Triticeae Consortium Mainly concerned with the International Triticeae Meeting. Site includes genome tables for Triticeae.
• GrainGenes: Triticeae Taxonomy
• Annual Wheat Newsletter

• Wheat: the big picture Illustrated guide to life cycle of wheat plant

• Wheat
• Plant taxonomies

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