Oat (Avena L.) includes 29 to 31 species (depending on the classification scheme) of wild and domesticated annual grasses in the family Gramineae (Poaceae) that comprise a polyploid series, with diploid, hexaploid, and tetraploid forms (Baum 1977; Leggett 1992). The primary cultivated species are hexaploids, A. sativa L. and A. byzantina C. Koch, although 5 other species have to some extent been cultivated for human consumption. These are the tetraploid A. abyssinica Hochst and the diploids A. strigosa Schreb., A. brevis Roth., A. hispanica Ard., and A. nuda L. Nevertheless, oat consumed in human diets this century has been almost exclusively hexaploids.

The separation of the two cultivated hexaploids is based on minor, and not always definitive, morphological differences and is of more historical than contemporary relevance. A. byzantina (red oat) was the original germ plasm base of most North American fall-sown cultivars, whereas A. sativa was the germ plasm base of spring-sown cultivars. Late twentieth-century breeding populations in both ecogeographic regions contain intercrosses of both species. This has led to the almost exclusive use of the term A. sativa in describing new cultivar releases.

Oat is the fifth most economically important cereal in world production after wheat, rice, corn, and barley. It is cultivated in temperate regions worldwide, especially those of North America and Europe, where it is well adapted to climatic conditions of adequate rainfall, relatively cool temperatures, and long days (Sorrells and Simmons 1992). Oat is used primarily for animal feed, although human consumption has increased in recent years.