According to Langenscheidt Fachwoerterbuch Landwirtschaft

Bread wheat is sown either in winter or in spring, depending on local climatic conditions. Spring wheat is generally confined to a relatively low altitude (0-800m) where winters are mild, such as the Arabian Peninsula, the Nile Valley, North Africa and parts of Central and West Asia. Winter wheat (and semi-winter or facultative wheat) is more suited to continental or highland areas such as those in Iran, Uzbekistan, and Afghanistan. Both winter and facultative wheat contain genes for vernalization, which enable the plants to tolerate cold conditions and promote a longer growing period. Crosses between spring, facultative, and winter wheat can expand the variety of germplasm available for selection and provide cultivars.
http://www.icarda.org/Publications/AnnualReport/2000/Project...


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Note added at 23 mins (2012-04-20 15:35:14 GMT)
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Intermediate (alternate or facultative) wheat
They differ from winter wheats in that they do not need low temperatures in order to flower. They differ from spring wheats in that they do not normally develop during the short, cold winter days. Some varieties will only grow well when sown in the autumn.
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