Temporal range: Paleogene–Present possible Late Cretaceous records
|Foliage and acorns of Quercus robur|
An oak is a tree or shrub in the genus Quercus (//; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably Lithocarpus (stone oaks), as well as in those of unrelated species such as Grevillea robusta (silky oaks) and the Casuarinaceae (she-oaks). The genus Quercus is native to the Northern Hemisphere, and includes deciduous and evergreen species extending from cool temperate to tropical latitudes in the Americas, Asia, Europe, and North Africa. North America contains the largest number of oak species, with approximately 90 occurring in the United States, while Mexico has 160 species of which 109 are endemic. The second greatest center of oak diversity is China, which contains approximately 100 species.
Oaks have spirally arranged leaves, with lobate margins in many species; some have serrated leaves or entire leaves with smooth margins. Many deciduous species are marcescent, not dropping dead leaves until spring. In spring, a single oak tree produces both male flowers (in the form of catkins) and small female flowers, meaning that the trees are monoecious. The fruit is a nut called an acorn or oak nut borne in a cup-like structure known as a cupule; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on their species. The acorns and leaves contain tannic acid, which helps to guard from fungi and insects. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.
- Sunset Western Garden Book, 1995, Leisure Arts, pp. 606–607, ISBN 0376038519.
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- Hogan, C. Michael (2012) "Oak" Archived 23 May 2013 at the Wayback Machine. ed. Arthur Dawson. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC
- Conrad, Jim. "Oak Flowers" Archived 4 November 2013 at the Wayback Machine. backyardnature.com. 2011-12-12. Retrieved 2013-11-03.
- Tull, Delena (1 January 1999). Edible and Useful Plants of Texas and the Southwest: A Practical Guide. University of Texas Press. ISBN 9780292781641. Archived from the original on 15 February 2017.
- Hipp, Andrew (2004). Oak Trees Inside and Out. Rosen Publishing Group, Inc. p. 4.