Taxonomy of wheat

During 10,000 years of cultivation, numerous forms of

• 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 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]

• A^m, also called A^b – present in wild einkorn (T. boeoticum).
• A – present in T. urartu[9] (closely related to T. boeoticum but not interfertile).
• B – present in most tetraploid wheats. Source not identified, but similar to Ae. speltoides.^[9]
• G – present in timopheevii group of wheats. Source not identified, but similar to Ae. speltoides.
• D – present in Ae. 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 in Triticum this translates into five super species:

• A^m T. monococcum
• A^u T. urartu
• BA^u T. turgidum
• GA^m T. timopheevii
• BA^uD, T. aestivum

For a larger list of genome names, see Triticeae § Genetics.

Domestication

There are four wild species, all growing in rocky habitats in the

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.^[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 the Pre-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.

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).

The term "cultivar" (abbreviated as cv.) 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 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 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 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

This section is missing information about genome and ploidy, if possible. Please expand the section to include this information. Further details may exist on the talk 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:

• Zhebrak – (T. aestivum × T. timopheevi
  )
• Triticum × fungicidum Zhuk. – Hexaploid, artificial cross (T. carthlicum × T. timopheevi)
• Triticum jakubzineri Udachin & Shakhm.
• Triticum militinae Zhuk. & Migush.
  – mutant form of T. timopheevi.
• Triticum petropavlovskyi Udachin & Migush.
• Triticum sinskajae Filat. & Kurkiev – mutant, free-threshing form of T. monococcum.
• Triticum × timococcum Kostov
• Triticum timonovum Heslot & Ferrary – Hexaploid, artificial cross.
• Triticum zhukovskyi Menabde & Ericzjan (T. timopheevi × T. monococcum): 6N^[6]