Wine barrels are made of oak; these are used for aging alcoholic beverages such as sherry and whisky, giving them a range of flavours, colours, and aromas.

[11] 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.

[14] The genus crossed the isthmus of Panama when the northern and southern continents came together[15] and is present as one species, Q. humboldtii, above 1,000 metres in Colombia.

[14] The oaks of North America are of many sections (Protobalanus, Lobatae, Ponticae, Quercus, and Virentes) along with related genera such as Notholithocarpus.

Oaks of section Cyclobalanopsis extend in a narrow belt along the Himalayas to cover mainland and island Southeast Asia as far as Sumatra, Java, Borneo, and Palawan.

[7][16] Finally, oaks of multiple sections (Cyclobalanopsis, Ilex, Cerris, Quercus and related genera like Lithocarpus and Castanopsis) extend across east Asia including China, Korea, and Japan.

[12] Potential records of Quercus have been reported from Late Cretaceous deposits in North America and East Asia.

These are not considered definitive, as macrofossils older than the Paleogene, and possibly from before the Eocene are mostly poorly preserved without critical features for certain identification.

Amongst the oldest unequivocal records of Quercus are pollen from Austria, dating to the Paleocene-Eocene boundary, around 55 million years ago.

[24] In addition, hundreds of oak species have been compared (at RAD-seq loci), allowing a detailed phylogeny to be constructed.

The phylogeny from Hipp et al. 2019 is:[25] CTB lineage Cyclobalanoides Glauca Acuta Semiserrata East Asian Cerris West Eurasian Cerris Early-diverging Ilex East Asian Ilex Himalaya-Mediterranean Himalayan subalpine Agrifoliae Palustres Coccineae (Rubrae) Phellos (Laurifoliae) Texas red oaks Erythromexicana

Dumosae Prinoids Albae Roburoids Stellatae Texas white oaks Leucomexicana The genus Quercus was circumscribed by Carl Linnaeus in the first edition of his 1753 Species Plantarum.

Ecological stresses, especially near habitat margins, can also cause a breakdown of mate recognition as well as a reduction of male function (pollen quantity and quality) in one parent species.

[49] The maintenance of particular loci for adaptation to ecological niches may explain the retention of species identity despite significant gene flow.

"[53] By this definition, many species of Quercus would be lumped together according to their geographic and ecological habitat, despite clear distinctions in morphology and genetic data.

The caterpillars of this species defoliate the trees and are hazardous to human health; their bodies are covered with poisonous hairs which can cause rashes and respiratory problems.

[61] Japanese oak wilt, caused by the fungus Raffaelea quercivora, has rapidly killed trees across Japan.

[63] The leaves and acorns of oaks are poisonous to livestock, including cattle and horses, if eaten in large amounts, due to the toxin tannic acid, which causes kidney damage and gastroenteritis.

[64][65] An exception is the domestic pig, which, under the right conditions, may be fed entirely on acorns,[66] and has traditionally been pastured in oak woodlands (such as the Spanish dehesa[67] and the English system of pannage).

[75] In hill states of India such as Uttarakhand, along with being used for fuelwood and timber, oak wood is used for agricultural implements, while the leaves serve as fodder for livestock during lean periods.

[80] The dried bark of the white oak was used in traditional medical preparations; its tannic acid content made it astringent and antiseptic.

Oak barrels, which may be charred before use, contribute to their contents' colour, taste, and aroma, imparting a desirable oaky vanillin flavour.

[87][88] In Japan, Children's Day is celebrated with Kashiwa-mochi rice cakes, filled with a sweet red bean paste, and wrapped in a kashiwa oak leaf.

This species grows around the Mediterranean Sea; Portugal, Spain, Algeria, and Morocco produce most of the world's supply.

[92][93][94] In the Himalayan region of India, oak forests are being invaded by pine trees due to global warming.

[95] Over the past 200 years, large areas of oak forest in the highlands of Mexico, Central America, and the northern Andes have been cleared for coffee plantations and cattle ranching.

[96] In the US, entire oak ecosystems have declined due to a combination of factors thought to include fire suppression, increased consumption of acorns by growing mammal populations, herbivory of seedlings, and introduced pests.

[101] It is the national tree of many countries,[102] including the US,[103] Bulgaria, Croatia, Cyprus (golden oak), Estonia, France, Germany, Moldova, Jordan, Latvia, Lithuania, Poland, Romania, Serbia, and Wales.

Arrangements of oak leaves, acorns, and sprigs indicate different branches of the United States Navy staff corps officers.

[109] The prehistoric Indo-European tribes worshiped the oak and connected it with a thunder god, and this tradition descended to many classical cultures.