An oak is a tree or shrub in the genus Quercus of the beech family, Fagaceae, having approximately 600 extant species. The common name "oak" may also appear in the names of species in related genera, notably Lithocarpus. The genus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in Asia and the Americas.

Source: http://en.wikipedia.org/wiki/Oak
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