During 10,000 years of cultivation, numerous forms of
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
, many of them
hybrids, have developed under a combination of
artificial
Artificiality (the state of being artificial or manmade) is the state of being the product of intentional human manufacture, rather than occurring naturally through processes not involving or requiring human activity.
Connotations
Artificiality ...
and
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
. This diversity has led to much confusion in the naming of wheats. This article explains how genetic and morphological characteristics of wheat influence its classification, and gives the most common botanical names of wheat in current use (see ). Information on the cultivation and uses of wheat is at the main
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
page.
''Aegilops'' and ''Triticum''
The genus ''
Triticum
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologica ...
'' includes the
wild
Wild, wild, wilds or wild may refer to:
Common meanings
* Wild animal
* Wilderness, a wild natural environment
* Wildness, the quality of being wild or untamed
Art, media and entertainment Film and television
* ''Wild'' (2014 film), a 2014 A ...
and
domesticated species usually thought of as wheat.
In the 1950s growing awareness of the genetic similarity of the wild goatgrasses (''
Aegilops
''Aegilops'' is a genus of Eurasian and North American plants in the grass family, Poaceae. They are known generally as goatgrasses. '') led botanists such as Bowden to amalgamate ''Aegilops'' and ''Triticum'' as one genus, ''Triticum''. This approach is still followed by some (mainly geneticists), but has not been widely adopted by taxonomists.
''Aegilops'' is morphologically highly distinct from ''Triticum'', with rounded rather than keeled
glume
In botany, a glume is a bract (leaf-like structure) below a spikelet in the inflorescence (flower cluster) of grasses (Poaceae) or the flowers of sedges (Cyperaceae). There are two other types of bracts in the spikelets of grasses: the lemma and ...
s.
''Aegilops'' is important in wheat
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
because of its role in two important hybridisation events. Wild
emmer (''
T. dicoccoides'' and ''
T. araraticum'') resulted from the
hybridisation of a wild wheat, ''
T. urartu'', and an as yet unidentified goatgrass, probably closely related to ''
Ae. speltoides''.
Hexaploid
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...
wheats (e.g. ''
T. aestivum'' the most common and '' T. spelta'') are the result of a hybridisation between a domesticated
wheat, probably '' T. dicoccum'' or ''
T. durum'', and another goatgrass, ''Aegilops tauschii">Ae. tauschii'' (also known as ''Ae. squarrosa'').
The hexaploid genome is an allohexaploid">Triticum durum">T. durum'', and another goatgrass, ''Aegilops tauschii">Ae. tauschii'' (also known as ''Ae. squarrosa'').
The hexaploid genome is an allohexaploid composed of two copies each of three subgenomes, AABBDD.
The is from ''T. urartu'' (AA).
The is a descendant of the of an unidentified species related to ''Aegilops'' section ''
Sitopsis
''Aegilops'' is a genus of Eurasian and North American plants in the grass family, Poaceae. They are known generally as goatgrasses. '' (SS).
This natural
hybridization event happened ~30.8
MYA
Mya may refer to:
Brands and product names
* Mya (program), an intelligent personal assistant created by Motorola
* Mya (TV channel), an Italian Television channel
* Midwest Young Artists, a comprehensive youth music program
Codes
* Burmese ...
, yielding the tetraploid ''
T. diccocoides''.
In time this tetraploid gave rise to ''
T. turgidum'', which gave rise to modern
durum
Durum wheat (), also called pasta wheat or macaroni wheat (''Triticum durum'' or ''Triticum turgidum'' subsp. ''durum''), is a tetraploid species of wheat. It is the second most cultivated species of wheat after common wheat, although it represen ...
.
Then ~0.4 MYA ''T. diccocoides'' naturally crossed with ''Aegilops tauschii'' (DD), adding the and yielding the hexaploid.
Early taxonomy
Botanists of the classical period, such as
Columella, and in sixteenth and seventeenth century
herbal
A herbal is a book containing the names and descriptions of plants, usually with information on their medicinal, tonic, culinary, toxic, hallucinatory, aromatic, or magical powers, and the legends associated with them.Arber, p. 14. A herbal m ...
s, divided wheats into two groups, ''Triticum'' corresponding to free-threshing wheats, and ''Zea'' corresponding to hulled ('spelt') wheats.
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
recognised five species, all domesticated:
* ''
T. aestivum
Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield.
Ta ...
'' 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 as
winter- vs.
spring- forms. The wild wheats were not described until the mid-19th century because of the poor state of botanical exploration in the
Near East
The ''Near East''; he, המזרח הקרוב; arc, ܕܢܚܐ ܩܪܒ; fa, خاور نزدیک, Xāvar-e nazdik; tr, Yakın Doğu is a geographical term which roughly encompasses a transcontinental region in Western Asia, that was once the hist ...
, where they grow.
The development of a modern classification depended on the discovery, in the 1920s, that wheat was divided into 3
ploidy
Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mat ...
levels.
Important characters in wheat
Ploidy level
As with many
grasses
Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns and ...
,
polyploidy is common in wheat. There are two wild diploid (non-polyploid) wheats, ''
T. boeoticum'' and ''
T. urartu''. ''T. boeoticum'' is the wild ancestor of domesticated einkorn, ''
T. monococcum''. 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 are
tetraploid (4 sets of chromosomes, 2n=4x=28), or
hexaploid
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...
(6 sets of chromosomes, 2n=6x=42). The tetraploid wild wheats are wild emmer, ''
T. dicoccoides'', and ''
T. araraticum''. Wild emmer is the ancestor of all the domesticated tetraploid wheats, with one exception: ''T. araraticum'' is the wild ancestor of ''
T. timopheevi''.
There are no wild hexaploid wheats, although feral forms of
common wheat
Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield.
Ta ...
are sometimes found. Hexaploid wheats developed under
domestication. Genetic analysis has shown that the original hexaploid wheats were the result of a cross between a tetraploid domesticated wheat, such as ''T. dicoccum'' or ''T. durum'', and a wild goatgrass, ''Ae. tauschii''.
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 new
genomes
In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding gen ...
into a species. For example, ''Aegilops tauschii'' brought the D genome into hexaploid wheats, with enhanced cold-hardiness and some distinctive morphological features.
Genome
Observation of chromosome behaviour during
meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
, and the results of hybridisation experiments, have shown that
wheat genomes (complete complements of genetic matter) can be grouped into distinctive types. Each type has been given a name,
A,
B, and
D. 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.
In ''Triticum'', five genomes, all originally found in diploid species, have been identified:
*A
m – present in wild einkorn (''T. boeoticum'').
*A – present in ''T. urartu''
(closely related to ''T. boeoticum'' but not interfertile).
*B – present in most tetraploid wheats. Source not identified, but similar to ''Ae. speltoides''.
*G – present in ''timopheevi'' group of wheats. Source not identified, but similar to ''Ae. speltoides''.
*D – present in ''Ae. tauschii'', and thus in all hexaploid wheats.
[
]
The genetic approach to wheat taxonomy (see below) takes the genome composition as defining each species.
As there are five known combinations in ''Triticum'' this translates into five ''super'' species:
*A
m ''T. monococcum''
*A
u ''T. urartu''
*BA
u ''T. turgidum''
*GA
m ''T. timopheevi''
*BA
uD, ''T. aestivum''
For a larger list of genome names, see .
Domestication
There are four wild species, all growing in rocky habitats in the
fertile crescent
The Fertile Crescent ( ar, الهلال الخصيب) is a crescent-shaped region in the Middle East, spanning modern-day Iraq, Syria, Lebanon, Israel, Palestine and Jordan, together with the northern region of Kuwait, southeastern region of ...
of the
Near East
The ''Near East''; he, המזרח הקרוב; arc, ܕܢܚܐ ܩܪܒ; fa, خاور نزدیک, Xāvar-e nazdik; tr, Yakın Doğu is a geographical term which roughly encompasses a transcontinental region in Western Asia, that was once the hist ...
. All the other species are
domesticated. 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.
Hulled ''vs.'' free-threshing
All wild wheats are hulled: they have tough glumes (husks) that tightly enclose the grains. Each ''package'' of glumes, lemma and palaea, and grains is known as a spikelet. At maturity the rachis (central stalk of the cereal ear) disarticulates, allowing the spikelets to disperse.
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 the
Pre-Pottery Neolithic B
Pre-Pottery Neolithic B (PPNB) is part of the Pre-Pottery Neolithic, a Neolithic culture centered in upper Mesopotamia and the Levant, dating to years ago, that is, 8800–6500 BC. It was typed by British archaeologist Kathleen Kenyon during h ...
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.
For more information, see
Wheat: Hulled vs. free-threshing wheat
Morphology
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, but
Floras must be consulted for full descriptions and identification keys.
Traditional ''vs.'' genetic classifications
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). He, and subsequent proponents (usually geneticists), argued that forms that were interfertile should be treated as one species (the
biological species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexe ...
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.
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
Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield.
Ta ...
'', rather than the trinomials necessary in the genetic system, e.g.
''T. a.'' subsp. ''aestivum''. Both approaches are widely used.
Infraspecific classification
In the nineteenth century, elaborate schemes of classification were developed in which wheat ears were classified to botanical
variety 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 as
miracle wheat, a form of ''
T. turgidum'' with branched ears, known as
''T. t.'' L. var. ''mirabile'' Körn.
The term "
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
" (abbreviated as ''cv.'') is often confused with "
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
" 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 is ''T. 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.
Naming
Botanical names for wheat are generally expected to follow an existing classification, such as those listed as ''current'' by the .
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 the
taxobox on the Wheat page.
A general rule is that different 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.
Table of wheat species
Note: Blank common name indicates that no common name is in use in the English language.
Explanatory notes on selected names
*''Triticum boeoticum''
Boiss. is sometimes divided into two subspecies:
**''T. boeoticum''
Boiss. subsp. ''thaoudar''
(Reut. ex Hausskn.) E. Schiem. – with two grains in each spikelet, distributed to east of fertile crescent.
**''T. boeoticum''
Boiss. subsp. ''boeoticum'' – one grain in each spikelet, in Balkans.
*''Triticum dicoccum''
Schrank ex Schübler is also known as ''Triticum dicoccon''
Schrank.
*''Triticum aethiopicum''
Jakubz. is a variant form of ''T. durum'' found in Ethiopia. It is not usually regarded as a separate species.
*''Triticum karamyschevii''
Nevsky was previously known as ''Triticum paleocolchicum''
A. M. Menabde.
Artificial species and mutants
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 × borisovii
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeological ...
''
Zhebrak
Anton Romanovich Zhebrak (Belarusian: Антон Раманавіч Жэбрак; 27 December 1901 – 20 May 1965) was a Soviet botanist, geneticist and professor.
Career
He was born in to a peasant family. Zhebrak received his undergraduate d ...
– (''
T. aestivum
Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield.
Ta ...
'' × ''
T. timopheevi'')
*''
Triticum × fungicidum''
Zhuk. – Hexaploid, artificial cross (''
T. carthlicum'' × ''T. timopheevi'')
*''
Triticum jakubzineri
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeological ...
''
Udachin &
Shakhm.
*''
Triticum militinae
''Triticum timopheevii'', Timopheev's wheat or Zanduri wheat, is a tetraploid wheat that has both cultivated and wild forms. It is believed to have evolved in isolation from the more common '' Triticum turgidum''; hybrids between T. timopheevii ...
'' Zhuk. &
Migush. – mutant form of ''T. timopheevi''.
*''
Triticum petropavlovskyi
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologica ...
'' Udachin & Migush.
*''
Triticum sinskajae
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeological ...
''
Filat. &
Kurkiev – mutant, free-threshing form of ''
T. monococcum''.
*''
Triticum × timococcum'' Kostov
*''
Triticum timonovum
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeological ...
'' Heslot & Ferrary – Hexaploid, artificial cross.
*''
Triticum zhukovskyi
''Triticum zhukovskyi'', or Zhukovsky's wheat, is a hexaploid wheat, very closely resembling the Triticum timopheevii, a tetraploid variety of wheat. ''T. zhukovskyi'' was first observed in Western Georgia in close proximity to ''Triticum timoph ...
''
Menabde &
Ericzjan (''T. timopheevi'' × ''T. monococcum'')
See also
*
Winter wheat
Winter wheat (usually ''Triticum aestivum'') are strains of wheat that are planted in the autumn to germinate and develop into young plants that remain in the vegetative phase during the winter and resume growth in early spring. Classification ...
vs.
spring wheat
*
Cultivated plant taxonomy
*
List of Canadian Heritage Wheat Varieties
'Red Fife' was the first named variety of wheat developed in Canada. Plant breeders continue to use heritage wheat varieties in order to develop new varieties.
Farmers are growing heritage wheat varieties as part of the 100 Mile Diet, 'eat local ...
References
Sources
*
*
*
* Lists of ''Triticum'' names. An essential tool.
* Includes links to USDA germplasm collection, and public domain images
Germplasm Resources Information Network (GRIN)
*
External links
Taxonomy
Les meilleurs blés (1880 and 1909)Also o
Pl@ntUse Beautifully illustrated French book on wheats then in cultivation and studied by the French breeders family Vilmorin.
Genetics
Mainly concerned with the International Triticeae Meeting. Site includes genome tables for Triticeae.
GrainGenes: Triticeae TaxonomyAnnual Wheat Newsletter
Morphology
Wheat: the big pictureIllustrated guide to life cycle of wheat plant
{{DEFAULTSORT:Wheat taxonomy
.
wheat
Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...