Origin, Taxonomy, and Genetic Systems

Barley was one of the first domesticated cereals, most likely originating in the Fertile Crescent area of the Near East. Many references to barley and beer are found in early Egyptian and Sumerian writings that are more than 5000 years old. Archaeological evidence of barley cultivation has been found dating back to 8000 BC in Iran. There is now considerable evidence that the initial cultivation of barley in China and India occurred at a later date. Cultivated barley is one of 31 Hordeum species, belonging to the tribe Triticeae, family Poaceae. It is an annual diploid species with 2n=14 chromosomes. The genetic system is relatively simple, while the species is genetically diverse, making it an ideal study organism. Molecular evidence has revealed considerable homology between barley, wheat, and rye. Among the wild Hordeum, there are diploid, tetraploid, and hexaploid species. Many are perennial. The species are native in various parts of the world.

Barley has a single floret in each spikelet. There are three spikelets at each node, alternating on opposite sides of the barley head or spike. In two-rowed barley, the central floret is fertile and the two lateral florets are sterile, resulting in a single seed at each node, giving the head a flat appearance (see the picture on the far right). In six-rowed barley, all of the florets are fertile (see the head on the left side of the picture). The central seeds are round and fat, but the laterals tend to be slightly asymmetric. A single head of barley can produce up to 80 seeds.

Currently the wild ancestor of barley (H. vulgare subsp. spontaneum) is thought to be a subspecies of cultivated barley, and cultivated barley is classified in the subspecies vulgare. Wild barley has a brittle rachis and occurs only in the two-row form. Cultivated barley has a nonbrittle rachis and may be two-rowed or six-rowed. H. vulgare subsp. spontaneum may be a transitional form between the true progenitor of barley and the cultivated species.

Barley generally has several stems or tillers. The Barley tillers are round and erect, with conspicuous nodes and internodes. Like many grasses, the stem is hollow. The ability of the barley plant to send up new tillers in response to favorable environmental conditions is a useful mechanism for adapting to changes during the growing season.
Two-rowed varieties usually have a higher number of tillers per plant and larger, heavier seed than six-rowed varieties. Six-rowed varieties on the other hand, usually have more seeds per inflorescence. Thus the compensatory effects of yield components lead to similar levels of yield potential.
The straw of barley is generally weaker than wheat.