| Abstract: |
The grass family includes some 10,000 species, and it encompasses tremendous morphological, physiological, ecological, and genetic diversity. The phylogeny of the family is becoming increasingly well understood. There were two major radiations of grasses, an early diversification leading to the subfamilies Pooideae, Bambusoideae, and Oryzoideae, and a later one leading to Panicoideae, Chloridoideae, Centothecoideae, and Arundinoideae. The phylogeny can be used to determine the direction of changes in genome arrangement and genome size. The grass family includes all the major cereals, such as wheat, maize, rice, barley, and oats, and most of the minor grains as well, such as rye, common millet, finger millet, teff, and many others that are less familiar. It also includes such economically important species as sugar cane and sorghum. Understanding the grass family is thus central to understanding the crops that feed the world. The family encompasses far more physiological, morphological, and genetic diversity than just the major cereal crops. It is the fourth largest family of flowering plants, and is divided into 650 (1) to 765 (2, 3) genera. It includes 8,00010,000 species, which is about double the number of species of mammals (4), and roughly the same number as birds (5). Members of the family occur on all continents, including Antarctica, which means that there is a grass species adapted to virtually every terrestrial habitat on earth. The genomic similarities now being discovered among all the cereal crops imply that the entire family can be viewed as a single genetic system (6, 7). This means that the diversity in the family can potentially be harnessed for agronomic uses.
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