Taxonomy of wheat facts for kids

Wheat has been grown by humans for about 10,000 years. During this time, many different types of wheat have appeared. Some are natural, and some were created by people choosing the best plants to grow. This wide variety can make it confusing to name and sort them all. This article will help you understand how scientists classify wheat based on its genes and how it looks. You'll also learn the common scientific names used today. For more about how wheat is grown and used, check out the main wheat page.

Miracle wheat (Triticum turgidum var. mirabile).

Wheat's Family: Aegilops and Triticum

The group of plants called Triticum includes all the wild and farmed types of wheat we know.

In the 1950s, scientists realized that wild goatgrasses, called Aegilops, were very similar to wheat. Some botanists thought they should all be in one big group, Triticum. However, most scientists who classify plants still keep Aegilops and Triticum separate. This is because Aegilops plants look quite different from Triticum plants.

Aegilops plants are important because they played a big part in how wheat evolved. For example, wild emmer wheat (T. dicoccoides) came from a mix of wild wheat and a type of goatgrass. Also, hexaploid wheats, like the common bread wheat (T. aestivum), were formed when a farmed tetraploid wheat mixed with another goatgrass called Ae. tauschii.

How Wheat Was First Classified

Early plant scientists, like those in ancient Rome, sorted wheats into two main groups. One group was for wheats where the grains were easy to remove from their husks. The other group was for wheats that kept their husks tightly around the grains.

Carl Linnaeus, a famous scientist, named five types of farmed wheat:

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

Later, more types were added, but even small differences like growing in winter or spring were sometimes given their own species name. Wild wheats were not described until the mid-1800s. This was because the areas where they grew in the Near East had not been fully explored by botanists.

A big step in classifying wheat happened in the 1920s. Scientists discovered that wheat types could be grouped by how many sets of chromosomes they had.

Key Features for Classifying Wheat

Chromosome Sets (Ploidy Level)

Like many grasses, wheat often has multiple sets of chromosomes. This is called polyploidy. There are two wild diploid wheats, meaning they have two sets of chromosomes. These are T. boeoticum and T. urartu. T. boeoticum is the wild ancestor of farmed einkorn wheat. Each cell of these diploid wheats has 14 chromosomes (2 sets of 7).

Polyploid wheats can be tetraploid (four sets of chromosomes, 28 chromosomes total) or hexaploid (six sets of chromosomes, 42 chromosomes total). Wild emmer wheat is a tetraploid wild wheat. It is the ancestor of most farmed tetraploid wheats.

There are no wild hexaploid wheats. They developed after wheat was farmed by humans. Scientists found that hexaploid wheats came from a cross between a farmed tetraploid wheat and a wild goatgrass.

Understanding ploidy is important for three reasons:

• Wheats with the same number of chromosome sets are usually more closely related.
• Ploidy affects how the plant looks. For example, more chromosome sets often mean larger cells.
• Polyploidy can bring new genetic information into a species. For instance, the D genome from Aegilops tauschii gave hexaploid wheats better cold resistance.

Genetic Makeup (Genome)

Scientists study chromosomes and how plants breed to understand their genomes. A genome is the complete set of genetic information in a plant. Each type of genome is given a letter, like B or D. Plants that share the same genome can usually breed with each other.

Knowing the genome types helps scientists figure out how different wheat types formed. If two different diploid plants mix to create a new polyploid plant, the new plant will have both original genomes. This helps identify the original parent plants, even thousands of years later.

In Triticum wheat, five main genomes have been found:

• A^m – Found in wild einkorn (T. boeoticum).
• A – Found in T. urartu (similar to T. boeoticum but can't breed with it).
• B – Found in most tetraploid wheats. Its exact source is unknown but it's similar to Ae. speltoides.
• G – Found in the timopheevi group of wheats. Its source is also unknown but similar to Ae. speltoides.
• D – Found in Ae. tauschii and all hexaploid wheats.

Some scientists classify wheat based on its genome makeup. This leads to five "super species":

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

Farming Status (Domestication)

There are four wild wheat species. They all grow in rocky areas of the Fertile Crescent in the Near East. All other wheat types are farmed by humans. Even though wild and farmed wheats can breed with each other, they grow in completely different places. Traditional classification often gives more importance to whether a wheat is wild or farmed.

Hulled or Free-Threshing Wheat

All wild wheats are "hulled." This means their grains are tightly covered by tough husks called glumes. When the plant is ripe, the central stalk (rachis) breaks apart. This allows the spikelets (the part with the grains and husks) to scatter.

The first farmed wheats, einkorn and emmer, were also hulled. But their central stalks did not break apart easily when ripe. Around 8000 BC, new types of wheat appeared that were "free-threshing." These had lighter husks and strong central stalks that did not break apart. This made it much easier to get the grains out.

Whether a wheat is hulled or free-threshing is important for classification. This is because they are grown and processed differently after harvest. Hulled wheats need a lot more work to remove their tough husks.

For more details, see Wheat: Hulled vs. free-threshing wheat.

How Wheat Looks (Morphology)

Besides being hulled or free-threshing, other features of how wheat looks are important for classifying it. These include how loose or tight the spike (the top part of the wheat plant) is, or if the husks have wings. You can find full descriptions and ways to identify different types in plant guidebooks called Floras.

Different Ways to Classify Wheat

Since the 1930s, scientists have generally agreed on the different types of wheat. However, they disagree on whether these types should be called full species or smaller groups within a species.

Some scientists, usually those who study genetics, believe that any types of wheat that can breed with each other should be considered one species. For example, emmer and hard wheat can breed, so they would be seen as different types of one larger species. This is called the "genetic approach."

Other scientists use the "traditional approach." They give more importance to where different wheat types grow and how they look. They also find it more practical because it allows most wheat types to have a simple two-part Latin name, like Triticum aestivum. The genetic system often needs a three-part name. Both ways of classifying are used widely today.

Smaller Groups Within Species

In the 1800s, very detailed ways of classifying wheat were created. Wheat ears were sorted into botanical varieties based on things like the hairiness or color of the husks, or the color of the grain. These variety names are not used much anymore. But they are sometimes still used for special types, like miracle wheat. This is a type of T. turgidum with branched ears, known as T. turgidum L. var. mirabile Körn.

The word cultivar (short for cv.) is often confused with species. A cultivar is a specific group of a crop plant that farmers grow. It usually comes from planned plant breeding. Cultivar names always start with a capital letter and are often put in single quotes, like T. aestivum cv. 'Pioneer 2163'. Farmers might call a cultivar a "variety," but it's better to avoid this in writing to prevent confusion with botanical varieties. The term landrace refers to older, informal types of crop plants that farmers have grown for a long time.

Naming Wheat Types

When giving scientific names to wheat, it's best to follow an existing classification system. The systems listed by the Wheat Genetics Resource Center are good examples. If you prefer the genetic way of classifying, the GRIN classification is very complete. If you like the traditional way, Dorofeev's work is a good choice. Wikipedia's wheat pages generally follow a version of the Dorofeev system.

It's important to remember: do not mix different classification systems in the same article or book. Stick to one system so everyone understands how you are naming the wheat types.

Table of Wheat Species

This table shows different types of wheat using two common classification systems: the genetic approach and the traditional approach.

Note: If a common name is blank, it means there isn't a widely used English name for that type of wheat.

Lab-Created Wheat and Special Forms

Scientists have given scientific names to wheat types created in labs through genetic experiments. Since these only exist in a lab, some question if they should have formal botanical names. Names have also been given to rare mutant forms of wheat. Here are a few examples:

• Triticum × borisovii Zhebrak – This is a mix of T. aestivum and T. timopheevi.
• Triticum × fungicidum Zhuk. – A hexaploid type created in the lab.
• Triticum sinskajae Filat. & Kurkiev – A mutant form of T. monococcum where the grains are easy to remove.
• Triticum zhukovskyi Menabde & Ericzjan – This is a mix of T. timopheevi and T. monococcum.