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{{Short description|Tree or shrub in the genus Quercus}}
{{redirect2|Oak tree|Quercus||Oak (disambiguation)|and|Oak Tree (disambiguation)|and|Quercus (disambiguation)}}
{{good article}}
{{Use dmy dates|date=July 2020}}
{{Automatic_taxobox
| name              = Oak
| fossil_range      = [[Paleocene]] - [[Eocene]] boundary – recent {{fossilrange|56|0}} possible Paleocene & Late Cretaceous records
| image             = Quercus robur.jpg
| image_caption     = Foliage and acorns of ''[[Quercus robur]]''
| taxon             = Quercus
| authority         = [[Carl Linnaeus|L.]]
| subdivision_ranks = Subgenera and sections
| subdivision       =
* [[Quercus subg. Cerris|''Quercus'' subg. ''Cerris'']]
** [[Quercus subg. Cerris#Section Cerris|''Quercus'' sect. ''Cerris'']]
** [[Quercus subg. Cerris#Section Cyclobalanopsis|''Quercus'' sect. ''Cyclobalanopsis'']]
** [[Quercus subg. Cerris#Section Ilex|''Quercus'' sect. ''Ilex'']] 
* [[Quercus subg. Quercus|''Quercus'' subg. ''Quercus'']]
** [[Quercus subg. Quercus#Section Lobatae|''Quercus'' sect. ''Lobatae'']]
** [[Quercus subg. Quercus#Section Ponticae|''Quercus'' sect. ''Ponticae'']] 
** [[Quercus subg. Quercus#Section Protobalanus|''Quercus'' sect. ''Protobalanus'']]
** [[Quercus subg. Quercus#Section Quercus|''Quercus'' sect. ''Quercus'']]
** [[Quercus subg. Quercus#Section Virentes|''Quercus'' sect. ''Virentes'']]

See also [[List of Quercus species|List of ''Quercus'' species]].
}}

An '''oak''' is a [[hardwood]] tree or shrub in the [[genus]] '''''Quercus''''' of the [[Fagaceae|beech family]]. They have spirally arranged leaves, often with lobed edges, and a nut called an [[acorn]], borne within a cup. The genus is widely distributed in the [[Northern Hemisphere]]; it includes some 500 species, both [[deciduous]] and [[evergreen]]. Fossil oaks date back to the Middle [[Eocene]]. [[Molecular phylogeny]] shows that the genus is divided into [[Old World]] and New World [[clade]]s, but many oak species [[Hybrid (biology)|hybridise]] freely, making the genus's history difficult to resolve.<!--Note: lead summaries cited text in body of article: citations are not repeated up here.-->

Ecologically, oaks are [[keystone species]] in habitats from Mediterranean semi-desert to subtropical [[rainforest]]. They live in association with many kinds of [[fungi]] including [[truffle]]s. Oaks support more than 950 species of [[caterpillar]], many kinds of [[gall wasp]] which form distinctive [[gall]]s (roundish woody lumps such as the [[oak apple]]), and a large number of pests and diseases. Oak leaves and acorns contain enough [[tannin]] to be toxic to cattle, but pigs are able to digest them safely. Oak timber is strong and hard, and has found many uses in construction and furniture-making. The bark was traditionally used for [[tanning leather]]. [[Oak (wine)|Wine barrel]]s 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. The spongy bark of the [[cork oak]] is used to make traditional wine bottle corks. Almost a third of oak species are threatened with extinction due to climate change, [[invasive pests]], and [[habitat loss]].<!--per MoS, lead summarizes cited claims in body of article but does not repeat the citations-->

In culture, the oak tree is a symbol of strength and serves as the [[national tree]] of many countries. In Indo-European and related religions, the oak is associated with [[thunder god]]s. Individual oak trees of cultural significance include the [[Royal Oak]] in Britain, the [[Charter Oak]] in the United States, and the [[Gernikako Arbola|Guernica Oak]] in the [[Basque Country (greater region)|Basque Country]].<!--per MoS, lead summarizes cited claims in body of article but does not repeat the citations-->

== Etymology ==

The [[genus|generic]] name ''Quercus'' is [[Latin]] for "oak", derived from [[Proto-Indo-European language|Proto-Indo-European]] ''*kwerkwu-'', "oak", which is also the origin of the name "[[fir]]", another important or sacred tree in Indo-European culture. The word "cork", for the bark of the [[cork oak]], similarly derives from ''Quercus''.<ref>{{cite web |title=Quercus (n.) |url=https://www.etymonline.com/word/quercus |website=Online Etymology Dictionary |access-date=1 October 2023}}</ref> The common name "oak" is from [[Old English]] ''ac'' (seen in placenames such as [[Acton, London|Acton]], from ''ac'' + ''tun'', "oak village"),<ref>{{cite book |last=Mills |first=A. D. |title=A Dictionary of English Place-Names |date=1993 |orig-year=1991 |publisher=[[Oxford University Press]] |isbn=978-0-19-283131-6 |page=2}}</ref> which in turn is from [[Proto-Germanic language|Proto-Germanic]] ''*aiks'', "oak".<ref>{{cite web |title=Quercus (n.) |url=https://www.etymonline.com/word/oak |website=Online Etymology Dictionary |access-date=1 October 2023}}</ref>

== Description ==

Oaks are [[hardwood]] ([[dicotyledon]]ous) trees, [[deciduous]] or [[evergreen]], with spirally arranged leaves, often with [[Dentate leaf|lobate margins]]; some have [[serrated leaves]] or [[Entire (botany)|entire leaves]] with smooth margins. Many deciduous species are [[marcescent]], not dropping dead leaves until spring. In spring, a single oak tree [[Monoecy|produces both]] male and female flowers. The [[staminate]] (male) flowers are arranged in [[catkin]]s, while the small [[pistillate]] (female) flowers<ref>{{cite web |last=Conrad |first=Jim |url=http://www.backyardnature.net/fl_bloak.htm |title=Oak Flowers |archive-url=https://web.archive.org/web/20131104064011/http://www.backyardnature.net/fl_bloak.htm |archive-date=4 November 2013 |website=Backyardnature.com |date=12 December 2011}}</ref> produce an [[acorn]] (a&nbsp;kind of [[Nut (fruit)|nut]]) contained in a [[Calybium and cupule|cupule]]. Each acorn usually contains one seed and takes 6–18 months to mature, depending on the species. The acorns and leaves contain [[tannic acid]],<ref>{{Cite book |last=Tull |first=Delena  |url=https://books.google.com/books?id=pnnHgcasN-cC&pg=PA102 |title=Edible and Useful Plants of Texas and the Southwest: A Practical Guide |date=1999 |publisher=University of Texas Press |isbn=978-0-2927-8164-1 |url-status=live |archive-url=https://web.archive.org/web/20170215071946/https://books.google.com/books?id=pnnHgcasN-cC&pg=PA102 |archive-date=15 February 2017}}</ref> which helps to guard against fungi and insects.<ref>{{Cite book |last=Hipp |first=Andrew |title=Oak Trees Inside and Out |publisher=Rosen Publishing |year=2004 |page=4}}</ref> There are some 500 extant species of oaks.<ref name=powo>{{cite web |title=''Quercus'' L. |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:325819-2 |website=Plants of the World Online |publisher=[[Royal Botanic Gardens, Kew]] |access-date=30 September 2020}}</ref>

Trees in the genus are often large and slow-growing; ''Q.&nbsp;alba'' can reach an age of 600 years, a diameter of {{convert|13|ft|m}} and a height of {{convert|145|ft|m}}.<ref name="Core">{{cite web |last1=Core |first1=Earl L. |title=Silvical Characteristics of the Five Upland Oaks |url=https://www.nrs.fs.usda.gov/pubs/other/oak_sym/oak_symposium_proceedings_019.pdf |publisher=United States Department of Agriculture |access-date=5 October 2023 |pages=19–22}}</ref> The [[Granit oak]] in Bulgaria, a ''Q.&nbsp;robur'' specimen, has an estimated age of 1,637 years, making it the oldest oak in Europe.<ref>{{cite web |last=Todorov |first=Radoslav |title=Знаете ли кои са най-старите живи организми? |url=https://chr.bg/zhivot/znaete-li-koi-sa-naj-starite-zhivi-organizmi/ |trans-title=Do you know which are the oldest living organisms? |website=Chronicle.B |access-date=5 October 2023 |language=Bulgarian |date=30 September 2018}}</ref> The Wi'aaSal tree, a [[live oak]] in the reservation of the [[Pechanga Band of Indians]], California, is at least 1,000 years old, and might be as much as 2,000 years old, which would make it the oldest oak in the US.<ref>{{cite web |title=The Largest Oak Trees in the World |url=https://hardwoodsgroup.com/the-largest-oak-trees-in-the-world/ |website=Hardwoods Group |date=27 July 2021 |access-date=5 October 2023}}</ref> Among the smallest oaks is ''[[Quercus acuta|Q.&nbsp;acuta]]'', the Japanese evergreen oak. It forms a bush or small tree to a height of some {{convert|30|ft|m}}.<ref>{{cite web |last1=Gilman |first1=Edward F. |last2=Watson |first2=Dennis G. |title=''Quercus acuta'': Japanese Evergreen Oak |url=https://edis.ifas.ufl.edu/publication/ST539 |publisher=IFAS |access-date=5 October 2023}}</ref>

<gallery mode="packed" heights="220px">
File:Brockwell Oak (9).jpg|''[[Quercus robur]]'' habit
File:Quercus lusitanica - Köhler–s Medizinal-Pflanzen-253.jpg|Illustration of ''[[Quercus lusitanica|Q.&nbsp;lusitanica]]'' showing [[staminate]] (left) and [[pistillate]] flowers (right)
File:2021-04-22 18 54 32 Male flowers (catkins) on a White Oak within a wooded area in the Franklin Farm section of Oak Hill, Fairfax County, Virginia.jpg|Catkins of ''[[Quercus alba|Q.&nbsp;alba]]'' containing the staminate or 'male' flowers
File:Летен дъб - цъфтеж, нови листа.JPG|New leaves and reddish pistillate or 'female' flowers of ''[[Quercus robur|Q.&nbsp;robur]]''
</gallery>

== Distribution ==

[[File:Quercus Global Distribution.svg|thumb|upright=2| Global distribution of ''Quercus''. The New and Old World parts are mostly separate [[clade]]s.{{efn|The New World sections are ''Protobalanus'', ''Lobatae'', ''Ponticae'', ''Quercus'', and ''Virentes''. Old World sections are ''Cerris'', ''Ilex'' and ''Cyclobalanopsis''.}} Red: North American.{{efn|The North American sections are ''Protobalanus'', ''Lobatae'', ''Ponticae'', ''Quercus'', and ''Virentes''.}} Pink: Central American.{{efn|The Central American sections are ''Virentes'', ''Quercus'' and ''Lobatae''}} Yellow: European.{{efn|The European sections are ''Quercus'', ''Cerris'' and ''Ilex''.}} Green: West/Central Asian.{{efn|The West/Central Asian sections are ''Ponticae'', ''Quercus'', ''Cerris'' and ''Ilex''.}} Turquoise: Southeast Asian.{{efn|The Southeast Asian sections are ''Quercus'', ''Cyclobalanopsis'', ''Cerris'' and ''Ilex''.}} Blue: East Asian.{{efn|The East Asian sections are ''Quercus'', ''Cerris'', ''Ilex'' and ''Cyclobalanopsis''.}}<ref name="Liu Yang Tian Yang 2023"/> See Phylogeny chapter/tree for sections.{{what|reason=Where would one find this?|date=January 2025}}]]

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 has the largest number of oak species, with approximately 160 species in Mexico, of which 109 are endemic, and about 90 in the United States. The second greatest area of oak diversity is China, with approximately 100 species.<ref>Hogan, C. Michael (2012) [http://www.eoearth.org/article/Oak "Oak"] {{webarchive |url=https://web.archive.org/web/20130523173442/http://www.eoearth.org/article/Oak |date=23 May 2013 }}. ed. Arthur Dawson. ''Encyclopedia of Earth''. National Council for Science and the Environment. Washington DC</ref>

In the Americas, ''Quercus'' is widespread from [[Vancouver]] and [[Nova Scotia]] in the south of Canada, south to [[Mexico]] and across the whole of the eastern United States. It is present in a small area of the west of [[Cuba]]; in [[Mesoamerica]] it occurs mainly above {{convert|1,000|m}}.<ref name="Nixon 2006"/> The genus crossed the [[isthmus of Panama]] when the northern and southern continents came together<ref name="Hooghiemstra 2006">{{cite book |last=Hooghiemstra |first=H. |chapter=Immigration of Oak into Northern South America: A Paleo-Ecological Document |title=Ecology and conservation of neotropical montane oak forests |publisher=Springer |year=2006 |pages=17–28 |chapter-url=}}</ref> and is present as one species, ''Q.&nbsp;humboldtii'', above 1,000&nbsp;metres in Colombia.<ref name="Nixon 2006">{{cite book |last=Nixon |first=Kevin C. |chapter=Global and neotropical distribution and diversity of oak (genus ''Quercus'') and oak forests |title=Ecology and conservation of neotropical montane oak forests |publisher=Springer |year=2006 |pages=3–13 |chapter-url=https://www.researchgate.net/publication/226843540}}</ref> The oaks of North America are of many sections (''Protobalanus'', ''Lobatae'', ''Ponticae'', ''Quercus'', and ''Virentes'') along with related genera such as ''Notholithocarpus''.<ref name="Liu Yang Tian Yang 2023"/>

In the Old World, oaks of section ''Quercus'' extend across the whole of Europe including European Russia apart from the far north, and north Africa (north of the Sahara) from Morocco to Libya. In Mediterranean Europe, they are joined by oaks of the sections ''Cerris'' and ''Ilex'', which extend across Turkey, the Middle East, Iran, Afghanistan and Pakistan'','' while section ''Ponticae'' is endemic to the western Caucasus in [[Turkey]] and [[Georgia (country)|Georgia]]. 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]].<ref name=powo/><ref>{{cite journal |last=Jablonski |first=Eike |title=Among the Oaks of Borneo and Java |journal=International Oaks |issue=10, Spring 2000 |date=2000 |url=http://www.internationaloaksociety.org/content/international-oaks-no-10-2000}}</ref> 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.<ref name="Liu Yang Tian Yang 2023">{{citation |last1=Liu |first1=Shuiyin |last2=Yang |first2=Yingying |last3=Tian |first3=Qin |last4=Yang |first4=Zhiyun |last5=Li |first5=Shufeng |last6=Valdes |first6=Paul J. |last7=Farnsworth |first7=Alex |last8=Kates |first8=Heather R. |last9=Siniscalchi |first9=Carolina M. |last10=Guralnick |first10=Robert P. |last11=Soltis |first11=Douglas E. |last12=Soltis |first12=Pamela S. |last13=Stull |first13=Gregory W. |last14=Folk |first14=Ryan A. |last15=Yi |first15=Tingshuang |display-authors=3 |title=Phylogenomic Analyses Reveal Widespread Gene Flow During the Early Radiation of Oaks and Relatives (Fagaceae: Quercoideae) |publisher=Cold Spring Harbor Laboratory |date=2023-04-28 |doi=10.1101/2023.04.25.538215 |s2cid=258428911 }}</ref>

== Evolution ==

=== Fossil history ===

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. The oldest records of ''Quercus'' in North America are from [[Oregon]], dating to the Middle Eocene, around 44 million years ago, with the oldest records in Asia from the Middle Eocene of Japan; both forms have affinities to the ''[[Cyclobalanopsis]]'' group.<ref>{{Citation |last1=Barrón |first1=Eduardo |title=The Fossil History of ''Quercus'' |date=2017 |work=Oaks Physiological Ecology. Exploring the Functional Diversity of Genus Quercus L. |volume=7 |pages=39–105 |editor-last=Gil-Pelegrín |editor-first=Eustaquio |place=Cham |publisher=Springer International Publishing |doi=10.1007/978-3-319-69099-5_3 |isbn=978-3-319-69098-8 |last2=Averyanova |first2=Anna |last3=Kvaček |first3=Zlatko |last4=Momohara |first4=Arata |last5=Pigg |first5=Kathleen B. |last6=Popova |first6=Svetlana |last7=Postigo-Mijarra |first7=José María |last8=Tiffney |first8=Bruce H. |last9=Utescher |first9=Torsten |display-authors=3 |series=Tree Physiology |hdl=10261/277765 |editor2-last=Peguero-Pina |editor2-first=José Javier |editor3-last=Sancho-Knapik |editor3-first=Domingo |hdl-access=free }}</ref>

<gallery class=center mode=nolines widths=200px heights=200px>
File:Quercus hispanica 20170317.jpg|''[[Quercus × hispanica]]'' leaf. [[Miocene]], [[Lleida]], Spain
File:Quercus hiholensis acorn UWBM 56470-3 Pigg & Wehr 2002 Plt2 fig16.png|''[[Quercus hiholensis]]'' acorn, [[Langhian]] age (Middle Miocene), Washington State, US (c. 15 mya)
File:Quercus kobatakei leaf (cropped).jpg|''Quercus kobatakei'' leaf. Early [[Oligocene]], Japan
File:Early Oligocene oak acorn from Bridge Creek Flora.jpg|Early Oligocene acorn, Oregon, US (33 mya)
</gallery>

=== External phylogeny ===

''Quercus'' forms part, or rather two parts, of the Quercoideae subfamily of the [[Fagaceae]], the beech family. Modern [[molecular phylogenetics]] suggests the following relationships:<ref name="Manos Cannon Oh 2008">{{cite journal | last1=Manos | first1=Paul S. | last2=Cannon | first2=Charles H. | last3=Oh | first3=Sang-Hun | title=Phylogenetic Relationships and Taxonomic Status Of the Paleoendemic Fagaceae Of Western North America: Recognition Of A New Genus, Notholithocarpus | journal=Madroño | publisher=California Botanical Society | volume=55 | issue=3 | year=2008 | issn=0024-9637 | doi=10.3120/0024-9637-55.3.181 | pages=181–190| s2cid=85671229 | url=https://www.biodiversitylibrary.org/part/168898 }}</ref><ref name="Xiang Wang Li 2014">{{cite journal | last1=Xiang | first1=Xiao-Guo | last2=Wang | first2=Wei | last3=Li | first3=Rui-Qi | last4=Lin | first4=Li | last5=Liu | first5=Yang | last6=Zhou | first6=Zhe-Kun | last7=Li | first7=Zhen-Yu | last8=Chen | first8=Zhi-Duan |display-authors=3 | title=Large-scale phylogenetic analyses reveal fagalean diversification promoted by the interplay of diaspores and environments in the Paleogene | journal=Perspectives in Plant Ecology, Evolution and Systematics | publisher=Elsevier BV | volume=16 | issue=3 | year=2014 | issn=1433-8319 | doi=10.1016/j.ppees.2014.03.001 | pages=101–110| bibcode=2014PPEES..16..101X }}</ref>

{{clade
|label1=[[Fagaceae]]
|1={{clade
   |label1=Fagoideae
   |1=''[[beech|Fagus]]'' (beeches)
   |label2=Quercoideae
   |2={{clade
      |1=''[[Trigonobalanus]]'' (3 evergreen species)
      |2={{clade
         |1={{clade
            |1=''[[Lithocarpus]]'' (stone oaks)
            |2=''[[Chrysolepis]]'' (chinquapins)
            }}
         |2={{clade
            |1='''''Quercus''' [[pro parte]]''
            |2={{clade
               |1=''[[Notholithocarpus]]'' (tan oak)
               |2={{clade
                 |1='''''Quercus''' [[pro parte]]''
                 |2={{clade
                   |1=''[[Castanopsis]]'' (also called chinquapins)
                   |2=''[[chestnut|Castanea]]'' (chestnuts)
                   }}
                }}
             }}
          }}
       }}
   }}
}}
}}

=== Internal phylogeny ===

Molecular techniques for phylogenetic analysis show that the genus ''Quercus'' consisted of [[Old World]] and [[New World]] clades.<ref name=":0"/><ref>{{Cite journal |last1=Hipp |first1=Andrew L. |last2=Manos|first2=Paul S. |last3=González-Rodríguez|first3=Antonio |last4=Hahn |first4=Marlene |last5=Kaproth|first5=Matthew |last6=McVay|first6=John D.| last7=Avalos|first7=Susana Valencia |last8=Cavender-Bares|first8=Jeannine |author-link8=Jeannine Cavender-Bares |display-authors=3 |date=January 2018 |title=Sympatric parallel diversification of major oak clades in the Americas and the origins of Mexican species diversity |journal=New Phytologist |volume=217 |issue=1 |pages=439–452 |doi=10.1111/nph.14773|pmid=28921530 |doi-access=free |bibcode=2018NewPh.217..439H |hdl=10161/15608|hdl-access=free }}</ref><ref>{{Cite journal |last1=Hubert|first1=François |last2=Grimm|first2=Guido W. |last3=Jousselin|first3=Emmanuelle |last4=Berry |first4=Vincent |last5=Franc|first5=Alain |last6=Kremer|first6=Antoine |display-authors=3 |date=2014-10-02 |title=Multiple nuclear genes stabilize the phylogenetic backbone of the genus ''Quercus'' |journal=Systematics and Biodiversity |volume=12 |issue=4 |pages=405–423 |doi=10.1080/14772000.2014.941037 |bibcode=2014SyBio..12..405H |s2cid=85604759 |issn=1477-2000 |url=https://figshare.com/articles/dataset/Multiple_nuclear_genes_stabilize_the_phylogenetic_backbone_of_the_genus_i_Quercus_i_/1128657|url-access=subscription }}</ref> The entire [[genome]] of ''Quercus robur'' (the pedunculate oak) has been [[DNA sequencing|sequenced]],<ref>{{Cite journal |last1=Plomion |first1=Christophe |last2=Aury |first2=Jean-Marc |last3=Amselem |first3=Joëlle |last4=Alaeitabar |first4=Tina |last5=Barbe |first5=Valérie |last6=Belser |first6=Caroline |last7=Bergès |first7=Hélène |last8=Bodénès |first8=Catherine |last9=Boudet|first9=Nathalie |last10=Boury |first10=Christophe |last11=Canaguier |first11=Aurélie |display-authors=3 |date=January 2016 |title=Decoding the oak genome: public release of sequence data, assembly, annotation and publication strategies |journal=Molecular Ecology Resources |volume=16 |issue=1|pages=254–265 |doi=10.1111/1755-0998.12425 |pmid=25944057 |s2cid=42715997|doi-access=free |bibcode=2016MolER..16..254P }}</ref> revealing an array of [[mutation]]s that may underlie the evolution of longevity and [[Plant disease resistance|disease resistance]] in oaks.<ref>{{Cite journal |last1=Plomion |first1=Christophe |last2=Aury |first2=Jean-Marc |last3=Amselem |first3=Joëlle |last4=Leroy |first4=Thibault |last5=Murat |first5=Florent |last6=Duplessis |first6=Sébastien |last7=Faye |first7=Sébastien |last8=Francillonne |first8=Nicolas |last9=Labadie |first9=Karine |last10=Le Provost |first10=Grégoire |last11=Lesur |first11=Isabelle |date=July 2018 |title=Oak genome reveals facets of long lifespan |journal=Nature Plants |volume=4 |issue=7 |pages=440–452 |doi=10.1038/s41477-018-0172-3 |pmc=6086335 |pmid=29915331|bibcode=2018NatPl...4..440P }}</ref> In addition, hundreds of oak species have been compared (at [[RAD-seq]] loci), allowing a detailed phylogeny to be constructed. However, the high signal of [[introgressive hybridization]] (the transfer of genetic material by repeated backcrossing with hybrid offspring) in the genus has made it difficult to resolve an unambiguous, unitary history of oaks. The phylogeny from Hipp et al. 2019 is:<ref>{{Cite journal |last1=Hipp |first1=Andrew L. |last2=Manos |first2=Paul S. |last3=Hahn |first3=Marlene |last4=Avishai |first4=Michael |last5=Bodénès |first5=Cathérine |last6=Cavender-Bares |first6=Jeannine|last7=Crowl |first7=Andrew A. |last8=Deng |first8=Min |last9=Denk |first9=Thomas |last10=Fitz-Gibbon |first10=Sorel |last11=Gailing |first11=Oliver |display-authors=3 |date=2019-10-14 |title=Genomic landscape of the global oak phylogeny |journal=New Phytologist |volume=226 |issue=4 |pages=1198–1212 |doi=10.1111/nph.16162 |pmid=31609470 |doi-access=free}}</ref>

{{clade |style=font-size:95%; line-height:105%;
|label1='''''Quercus'''''
|sublabel1= 56 [[Mya (geology)|mya]]
|1={{clade
   |label1=[[Quercus subg. Cerris|subgenus ''Cerris'']]
   |sublabel1=[[Old World]]
   |1={{clade
      |1={{clade
       |label1=section ''Cyclobalanopsis''
       |sublabel1= 44 [[Mya (geology)|mya]]
       |1={{clade
         |1={{clade
            |1=CTB<!--Compound [[Trichome]] Base--> lineage <!--e.g. Quercus chungii--> [[File:Quercus rex leaf white background.jpg|60px]]
            |2=Cyclobalanoides <!--Q. corrugata-->
            }}
         |2={{clade
            |1=Glauca [[File:Quercus glauca MHNT.BOT.2010.4.2 (cropped).jpg|80px]]
            |2={{clade
               |1=Acuta [[File:Quercus acuta2 (cropped).jpg|70px]]
               |2=Semiserrata <!--e.g. Quercus macrocalyx-->
               }}
            }}
          }}
         }}
      |2={{clade
         |label1=section ''Cerris''
         |1={{clade
            |1=East Asian Cerris [[File:Quercus acutissima leaf white background.jpg|70px]]
            |2=West Eurasian Cerris [[File:Quercus cerris leaf illustrations.jpg|80px]]
            }}
         |label2=section ''Ilex''
         |2={{clade
            |1={{clade
               |1=Early-diverging Ilex [[File:Macedonian Oak Quercus trojana white background.jpg|60px]]
               |2=East Asian Ilex [[File:Quercus phillyreoides leaf white background.jpg|50px]]
               }}
            |2={{clade
               |1=Himalaya-Mediterranean [[File:Quercus ilex leaf illustration.jpg|50px]]
               |2=Himalayan subalpine [[File:Quercus semecarpifolia leaf.jpg|60px]]
               }}
            }}
         }}
      }}
   |label2=[[Quercus subg. Quercus|subgenus ''Quercus'']]
   |sublabel2=[[New World]]
   |2={{clade
      |1={{clade
       |label1=section ''Lobatae''
       |1={{clade
         |1=Agrifoliae [[File:Quercus agrifolia leaf.JPG|40px]]
         |2={{clade
            |1=Palustres [[File:Quercus palustris leaf (white background).jpg|60px]]
            |2={{clade
               |1={{clade
                  |1=Coccineae (Rubrae) [[File:Quercus rubra-(EU).jpg|35px]]
                  |2=Phellos (Laurifoliae) [[File:Leaf_of_Willow_Oak_Quercus_phellos_white_background.jpg|60px]]
                  }}
               |2={{clade
                  |1=Texas red oaks [[File:Quercus buckleyi leaf.jpg|50px]]
                  |2=Erythromexicana [[File:Quercus hypoleucoides leaf white background.jpg|40px]]
                  }}
               }}
            }}
         }}
        }}
      |2={{clade
         |1={{clade
            |label1=section ''Protobalanus'' 
            |1=[[File:Quercus palmeri leaf white background.jpg|50px]]
            |label2=section ''Ponticae'' 
            |2=[[File:Quercus pontica leaf (white background).jpg|55px]]
            |sublabel2=[[New World]], C. Asia
            }}
         |2={{clade
            |label1=section ''Virentes'' 
            |1=[[File:Quercus oleoides leaf white background.jpg|55px]]
            |label2=section ''Quercus''
            |sublabel2=[[New World]], Europe
            |2={{clade
				|1={{clade
				   |1=Dumosae [[File:Quercus dumosa leaf (white background).jpg|33px]]
				   |2={{clade
					  |1={{clade
						 |1=Prinoids [[File:Quercus prinoides leaf white background.jpg|40px]]
						 |2={{clade
						    |1=Albae [[File:Quercus montana leaf white background.jpg|38px]]
                            |2=Roburoids [[File:Quercus robur leaf.jpg|40px]]
							}}
						 }}
					  |2={{clade
						 |1=Stellatae [[File:Quercus stellata (EU).jpg|40px]]
						 |2={{clade
							|1=Texas white oaks [[File:Autumn White Oak Leaf.jpg|40px]]
							|2=Leucomexicana [[File:Quercus rugosa leaf white background.jpg|55px]]
							}}
						 }}
					  }}
				   }}
			    }}
            }}
         }}
      }}
   }}
}}

=== Taxonomy ===

{{See also|List of Quercus species}}

==== Taxonomic history ====

The genus ''Quercus'' was [[circumscription (taxonomy)|circumscribed]] by [[Carl Linnaeus]] in the first edition of his 1753 ''[[Species Plantarum]]''.<ref>{{cite journal |last1=Pardo |first1=Francisco M. Vázquez |last2=Maqueda |first2=Soledad Ramos |last3=Pérez |first3=Esperanza Doncel |title=''Quercus ilex'' L. and ''Quercus rotundifolia'' Lam.: Two Different Species |journal=International Oaks |issue=13 |year=2002 |pages=9–14 |url=https://www.internationaloaksociety.org/sites/default/files//files/IO/IOS%20Journal%20%2313/International%20Oaks%20No.%2013%20-%20Quercus%20ilex%20L.%20and%20Quercus%20rotundifolia%20Lam.-%20Two%20Different%20Species%20-%20Franciso%20M.%20V%C3%A1zquez%20Pardo%2C%20Soledad%20Ramos%20Maqueda%2C%20Esperanza%20Doncel%20P%C3%A9rez.pdf}}</ref> He described 15 species within the new genus, providing type specimens for 10 of these, and giving names but no types for ''[[Quercus cerris|Q.&nbsp;cerris]]'', ''[[Quercus coccifera|Q.&nbsp;coccifera]]'', ''[[Quercus ilex|Q.&nbsp;ilex]]'', ''[[Quercus smilax|Q.&nbsp;smilax]]'', and ''[[Quercus suber|Q.&nbsp;suber]]''.<ref>{{cite journal |last1=Iamonico |first1=Duilio |last2=Peruzzi |first2=Lorenzo |title=Lectotypification of Linnaean Names in the Genus ''Quercus'' (Fagaceae) |journal=Taxon |volume=62 |issue=5 |year=2013 |pages=1041–1045 |doi=10.12705/625.5 |jstor=taxon.62.5.1041|bibcode=2013Taxon..62.1041I }}</ref> He chose ''[[Quercus robur|Q.&nbsp;robur]]'', the pedunculate oak, as the [[type species]] for the genus.<ref>{{cite journal |last1=Nixon |first1=Kevin C. |last2=Carpenter |first2=James M. |last3=Stevenson |first3=Dennis W. |title=The PhyloCode is fatally flawed, and the 'Linnaean' system can easily be fixed |journal=The Botanical Review |volume=69 |issue=1 |year=2003 |pages=111–120 |doi=10.1663/0006-8101(2003)069[0111:TPIFFA]2.0.CO;2 |s2cid=43477057 |url=http://lamarck.unl.edu/systematics/papers-pdf/BotRev691_111-120.pdf}}</ref>

A 2017 classification of ''Quercus'', based on multiple molecular phylogenetic studies, divided the genus into two [[subgenera]] and eight [[Section (botany)|sections]]:<ref name=DenkGrimManoDeng17>{{Citation |last1=Denk |first1=Thomas |last2=Grimm |first2=Guido W. |last3=Manos |first3=Paul S. |last4=Deng |first4=Min |last5=Hipp |first5=Andrew L. |display-authors=3 |title=Oaks Physiological Ecology. Exploring the Functional Diversity of Genus ''Quercus'' L |series=Tree Physiology |date=2017 |volume=7 |editor1-last=Gil-Pelegrín |editor1-first=Eustaquio |editor2-last=Peguero-Pina |editor2-first=José Javier |editor3-last=Sancho-Knapik |editor3-first=Domingo |contribution=An Updated Infrageneric Classification of the Oaks: Review of Previous Taxonomic Schemes and Synthesis of Evolutionary Patterns |pages=13–38 |publication-place=Cham. |publisher=Springer International Publishing |doi=10.1007/978-3-319-69099-5_2 |isbn=978-3-319-69099-5 |contribution-url=https://doi.org/10.1007/978-3-319-69099-5_2 |mode=cs1}}</ref>

*Subgenus ''Quercus'' – the New World clade (or high-latitude clade), mostly native to North America
**Section ''Lobatae'' <small>Loudon</small> – North American red oaks
**Section ''Protobalanus'' <small>(Trelease) O.Schwarz</small> – North American intermediate oaks
**Section ''Ponticae'' <small>Stef.</small> – with a [[disjunct distribution]] between western [[Eurasia]] and western North America
**Section ''Virentes'' <small>Loudon</small> – American southern live oaks
**Section ''Quercus'' – white oaks from North America and Eurasia
*Subgenus ''Cerris'' <small>Oerst.</small>  – the Old World clade (or mid-latitude clade), exclusively native to Eurasia
**Section ''Cyclobalanopsis'' <small>Oerst.</small> – cycle-cup oaks of East Asia
**Section ''Cerris'' <small>Dumort.</small> – cerris oaks of subtropical and temperate Eurasia and North Africa
**Section ''Ilex'' <small>Loudon</small> – ilex oaks of tropical and subtropical Eurasia and North Africa
<!--note --- these sections are clearly marked on the cladogram below-->

The subgenus division supports the evolutionary diversification of oaks among two distinct clades: the Old World clade (subgenus ''Cerris''), including oaks that diversified in Eurasia; and the New World clade (subgenus ''Quercus''), oaks that diversified mainly in the Americas.<ref name=":0">{{Cite journal |last1=Manos |first1=Paul S. |last2=Zhou |first2=Zhe-Kun |last3=Cannon |first3=Charles H. |year=2001 |title=Systematics of Fagaceae: Phylogenetic Tests of Reproductive Trait Evolution |journal=International Journal of Plant Sciences |volume=162 |issue=6 |pages=1361–1379 |doi=10.1086/322949 |jstor=10.1086/322949 |bibcode=2001IJPlS.162.1361M |s2cid=85925622}}</ref><ref name="Manos Hipp 2021">{{cite journal |last1=Manos |first1=Paul S. |last2=Hipp |first2=Andrew L. |title=An Updated Infrageneric Classification of the North American Oaks (''Quercus'' Subgenus ''Quercus''): Review of the Contribution of Phylogenomic Data to Biogeography and Species Diversity |journal=Forests |publisher=MDPI AG |volume=12 |issue=6 |date=2021-06-15 |issn=1999-4907 |doi=10.3390/f12060786 |page=786 |doi-access=free |bibcode=2021Fore...12..786M }}</ref>

==== Subgenus ''Quercus'' ====

{{main|Quercus subg. Quercus|l1=''Quercus'' subg. ''Quercus''}}

* Sect. ''Lobatae'' ([[Synonym (taxonomy)|synonym]] ''Erythrobalanus''), the [[Erythrobalanus|red oaks]] of North America, [[Central America]] and northern [[South America]]. [[Style (botany)|Style]]s are long; the acorns mature in 18 months and taste very bitter. The inside of the acorn shell appears woolly. The actual nut is encased in a thin, clinging, papery skin. The leaves typically have sharp lobe tips, with spiny bristles at the lobe.<ref name=DenkGrimManoDeng17/>
* Sect. ''Protobalanus'', the [[Protobalanus|canyon live oak and its relatives]], in the southwestern [[United States]] and northwest [[Mexico]]. Styles are short; the acorns mature in 18 months and taste very bitter. The inside of the acorn shell appears woolly. The leaves typically have sharp lobe tips, with bristles at the lobe tip.<ref name=DenkGrimManoDeng17/>
* Sect. ''Ponticae,'' a disjunct including just two species. Styles are short, and the acorns mature in 12 months. The leaves have large [[stipule]]s, high secondary veins, and are highly toothed.<ref name=DenkGrimManoDeng17/>
* Sect. ''Virentes,'' the southern live oaks of the Americas. Styles are short, and the acorns mature in 12 months. The leaves are evergreen or subevergreen.<ref name=DenkGrimManoDeng17/>
* Sect. ''Quercus'' (synonyms ''Lepidobalanus'' and ''Leucobalanus''), the [[Lepidobalanus|white oaks]] of [[Europe]], [[Asia]] and North America. Trees or shrubs that produce nuts, specifically acorns, as fruits. Acorns mature in one year for annual trees and two years for biannual trees. Acorn is encapsulated by a spiny cupule as characterized by the family Fagaceae. Flowers in the ''Quercus'' genera produce one flower per node, with three or six styles, as well as three or six [[Ovary (botany)|ovaries]], respectively. The leaves mostly lack a bristle on their lobe tips, which are usually rounded. The type species is ''[[Quercus robur]]''.<ref name=DenkGrimManoDeng17/><ref>{{Cite book |last=Hitchcock |first=C. Leo |url=https://www.worldcat.org/oclc/1027726223 |title=Flora of the Pacific Northwest : an illustrated manual |publisher=University of Washington Press |others=Arthur Cronquist, David Giblin, Ben Legler, Peter F. Zika, Richard G. Olmstead |year=2018 |isbn=978-0-295-74289-2 |edition=Second |location=Seattle |pages=221 |oclc=1027726223}}</ref>

==== Subgenus ''Cerris'' ====

{{main|Quercus subg. Cerris|l1=''Quercus'' subg. ''Cerris''}}

The type species is ''Quercus cerris''.
* Sect. ''[[List of Quercus species#Section Cyclobalanopsis|Cyclobalanopsis]]'', the [[List of Quercus species#Section Cyclobalanopsis|ring-cupped oaks]] of eastern and southeastern Asia. These are evergreen trees growing {{convert|10|–|40|m|ft|0|abbr=off}} tall. They are distinct from subgenus ''Quercus'' in that they have acorns with distinctive cups bearing concrescent rings of scales; they commonly also have densely clustered acorns, though this does not apply to all of the species. Species of ''Cyclobalanopsis'' are common in the evergreen subtropical [[laurel forest]]s, which extend from southern Japan, southern Korea, and Taiwan across southern China and northern Indochina to the eastern Himalayas, in association with trees of the genus ''[[Castanopsis]]'' and the laurel family ([[Lauraceae]]).<ref name=DenkGrimManoDeng17/>
* Sect. ''Cerris'', the [[Cerris|Turkey oak and its relatives]] of Europe and Asia. Styles are long; acorns mature in 18 months and taste very bitter. The inside of the acorn's shell is hairless. Its leaves typically have sharp lobe tips, with bristles at the lobe tip.<ref name=DenkGrimManoDeng17/>
* Sect. ''[[List of Quercus species#Section Ilex|Ilex]]'', the Ilex oak and its relatives of Eurasia and northern [[Africa]]. Styles are medium-long; acorns mature in 12–24 months, appearing hairy on the inside. The leaves are evergreen, with bristle-like extensions on the teeth.<ref name=DenkGrimManoDeng17/>

== Ecology ==

[[File:Oak leafroller larvae.png|thumb|left|upright=0.8|Caterpillars of the North American oak leafroller, ''[[Archips semiferanus]]'', can defoliate oak forests.]]

Oaks are [[keystone species]] in a wide range of habitats from Mediterranean semi-desert to subtropical rainforest. They are important components of hardwood forests; some species grow in associations with members of the [[Ericaceae]] in [[oak–heath forest]]s.<ref>[http://www.dcr.virginia.gov/natural_heritage/ncTIIIe.shtml ''The Natural Communities of Virginia Classification of Ecological Community Groups'' (Version 2.3), Virginia Department of Conservation and Recreation, 2010] {{webarchive |url=https://web.archive.org/web/20090115181617/http://www.dcr.virginia.gov/natural_heritage/ncTIIIe.shtml |date=15 January 2009 }}. Dcr.virginia.gov. Retrieved 2011-12-10.</ref><ref>Schafale, M. P. and A. S. Weakley. 1990. ''Classification of the natural communities of North Carolina: third approximation''. North Carolina Natural Heritage Program, North Carolina Division of Parks and Recreation.</ref> Several kinds of [[truffle]]s, including two well-known varieties – black [[Tuber melanosporum|Périgord truffle]]<ref>{{cite web |url=http://www.thenibble.com/reviews/main/vegetables/truffle-glossary6.asp#glossary |title=Truffle Glossary: Black Truffles |publisher=thenibble.com |date=2010-07-01 |access-date=1 July 2010 |url-status=live |archive-url=https://web.archive.org/web/20100419130742/http://www.thenibble.com/reviews/main/vegetables/truffle-glossary6.asp#glossary |archive-date=19 April 2010}}</ref> and the white Piedmont truffle<ref name=r13>{{cite web |url=http://www.thenibble.com/reviews/main/vegetables/truffle-glossary8.asp#glossary |title=Truffle Glossary: White Truffles |publisher=thenibble.com |date=2010-07-01 |access-date=1 July 2010 |url-status=live |archive-url=https://web.archive.org/web/20100925140942/http://www.thenibble.com/reviews/MAIN/vegetables/truffle-glossary8.asp#glossary |archive-date=25 September 2010}}</ref> – have symbiotic relationships with oak trees. Similarly, many other fungi, such as ''[[Ramaria flavosaponaria]]'', associate with oaks.<ref name="Nirschl">{{cite web |last1=Nirschl |first1=Rick |title=Mushrooms of the Oak Openings |url=http://www.toledonaturalist.org/~naturalist/wp-content/uploads/2018/01/fungifinal3_sheet1.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.toledonaturalist.org/~naturalist/wp-content/uploads/2018/01/fungifinal3_sheet1.pdf |archive-date=2022-10-09 |url-status=live |access-date=19 July 2018 |website=Toledo Naturalists' Association |page=4}}</ref><ref name="Petersen">{{cite journal |last1=Petersen |first1=Ronald H. |author-link1=Ron Petersen |date=November 1985 |title=Notes on Clavarioid Fungi. XX. New Taxa and Distributional Records in ''Clavulina'' and ''Ramaria'' |journal=Mycologia |publisher=Taylor & Francis |volume=77 |issue=6 |pages=903–919 |doi=10.2307/3793302 |issn=0027-5514 |jstor=3793302 |oclc=7377077277}}</ref>

Oaks support more than 950 species of caterpillars, an important food source for many birds.<ref>{{cite web |last1=Bryant |first1=Tracey |date=April 2021 |title=Planting For the Planet |publisher=University of Delaware |url=https://www.udel.edu/udaily/2021/april/doug-tallamy-earth-day-oak-sustainable-ecosystem/}}</ref> Mature oak trees shed widely varying numbers of acorns (known collectively as mast) annually, with large quantities in [[Mast (botany)|mast years]]. This may be a [[predator satiation]] strategy, increasing the chance that some acorns will survive to germination.<ref name="Bogdziewicz Marino Bonal Zwolak 2018 pp. 2575–2582">{{cite journal |last1=Bogdziewicz |first1=Michał |last2=Marino |first2=Shealyn |last3=Bonal |first3=Raul |last4=Zwolak |first4=Rafał |last5=Steele |first5=Michael A. |title=Rapid aggregative and reproductive responses of weevils to masting of North American oaks counteract predator satiation |journal=Ecology |publisher=Wiley |volume=99 |issue=11 |date=2018-09-28 |issn=0012-9658 |doi=10.1002/ecy.2510 |pages=2575–2582|pmid=30182480 |bibcode=2018Ecol...99.2575B |s2cid=52156639 |doi-access=free }}</ref>

[[File:Eurasian jay (32648148027) (cropped).jpg|thumb|[[Jay]]s feed on acorns and help to [[Seed dispersal|disperse these seeds]].]]

Animals including [[squirrel]]s<ref name="Steele Yi 2020">{{cite journal | last1=Steele | first1=Michael A. | last2=Yi | first2=Xianfeng | title=Squirrel-Seed Interactions: The Evolutionary Strategies and Impact of Squirrels as Both Seed Predators and Seed Dispersers | journal=Frontiers in Ecology and Evolution | publisher=Frontiers Media SA | volume=8 | date=4 August 2020 | issn=2296-701X | doi=10.3389/fevo.2020.00259 | page= | doi-access=free }}</ref> and jays – [[Eurasian jay]]s in the Old World, [[blue jay]]s in North America – feed on acorns, and are important agents of [[seed dispersal]] as they carry the acorns away and bury many of them as food stores.<ref name="Mitrus Szabo 2020">{{cite journal | last1=Mitrus | first1=Cezary | last2=Szabo | first2=Josif | title=Foraging Eurasian Jays ''(Garrulus glandarius)'' prefer oaks and acorns in central Europe | journal=Ornis Hungarica | publisher=Walter de Gruyter GmbH | volume=28 | issue=1 | date=1 June 2020 | issn=2061-9588 | doi=10.2478/orhu-2020-0010 | pages=169–175| s2cid=220634002 | doi-access=free }}</ref><ref name="Enroth 2022">{{cite web |last1=Enroth |first1=Christopher |title=Of blue jays and pin oaks: How jays have shaped our oak forests around the world |url=https://extension.illinois.edu/blogs/good-growing/2022-03-04-blue-jays-and-pin-oaks-how-jays-have-shaped-our-oak-forests-around |publisher=University of Illinois Urbana-Champaign |access-date=14 October 2023 |date=4 March 2022}}</ref><ref name="Bossema 1979">{{cite journal | last=Bossema | first=I. | title=Jays and Oaks: an Eco-Ethological Study of a Symbiosis | journal=Behaviour | publisher=Brill | volume=70 | issue=1–2 | year=1979 | issn=0005-7959 | doi=10.1163/156853979x00016 | pages=1–116| url=https://research.rug.nl/en/publications/dc64a15d-a47b-459d-94d3-36ee96189986 }}</ref> However, some species of squirrel selectively excise the embryos from the acorns that they store, meaning that the food store lasts longer and that the acorns will never germinate.<ref name="Steele Yi 2020"/>

=== Hybridisation ===

[[File:Quercus stellata.jpg|thumb|left|upright=0.9 |A hybrid white oak, possibly ''[[Post oak|Quercus stellata]]'' × ''[[Chinkapin oak|Q. muehlenbergii]]'']]

[[Interspecific hybridization]] is quite common among oaks, but usually between species within the same section only,<ref>{{Cite journal |last=Valen |first=Leigh Van |year=1976 |title=Ecological Species, Multispecies, and Oaks |journal=Taxon |volume=25 |issue=2/3 |pages=233–239 |doi=10.2307/1219444 |issn=0040-0262 |jstor=1219444|bibcode=1976Taxon..25..233V }}</ref> and most common in the white oak group. White oaks cannot discriminate against pollination by other species in the same section. Because they are [[wind pollinated]] and have weak internal barriers to hybridization, hybridization produces functional seeds and fertile hybrid offspring. 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.<ref>{{Cite journal|last1=Williams |first1=Joseph H. |first2=William J. |last2=Boecklen |first3=Daniel J. |last3=Howard |year=2001 |title=Reproductive processes in two oak (''Quercus'') contact zones with different levels of hybridization |journal=Heredity |volume=87 |issue=6 |pages=680–690 |doi=10.1046/j.1365-2540.2001.00968.x|pmid=11903563 |doi-access=free |bibcode=2001Hered..87..680W }}</ref><ref>{{Cite book|last=Arnold |first=M. L. |year=1997 |title=Natural Hybridization and Evolution |publisher=Oxford University Press |location=New York |isbn=0-19-509974-5}}</ref>

Frequent hybridization among oaks has consequences for oak populations around the world; most notably, hybridization has produced large populations of hybrids with much [[introgression]] and the [[evolution]] of new species.<ref name=r2>{{Cite journal|last1=Conte |first1=L. |last2=Cotti |first2=C. |last3=Cristofolini |first3=G. |year=2007 |title=Molecular evidence for hybrid origin of ''Quercus crenata'' Lam. (Fagaceae) from ''Q-cerris'' L. and ''Q-suber'' L. |journal=Plant Biosystems |volume=141 |issue=2 |pages=181–193 |doi=10.1080/11263500701401463|bibcode=2007PBios.141..181C |s2cid=83882998 }}</ref> Introgression has caused different species in the same populations to share up to 50% of their genetic information.<ref name=r3>{{cite journal |last1=Gomory |first1=D. |last2=Schmidtova |first2=J. |year=2007 |title=Extent of nuclear genome sharing among white oak species (''Quercus'' L. subgen. ''Lepidobalanus'' (Endl.) Oerst.) in Slovakia estimated by allozymes |journal=Plant Systematics and Evolution |volume=266 |issue=3–4 |pages=253–264 |doi=10.1007/s00606-007-0535-0|bibcode=2007PSyEv.266..253G |s2cid=23587024 }}</ref> As a result, genetic data often does not differentiate between clearly morphologically distinct species, but instead differentiates populations.<ref name=r4>{{Cite journal |last1=Kelleher |first1=C. T. |first2=T. R. |last2=Hodkinson |first3=G. C. |last3=Douglas |first4=D. L. |last4=Kelly |year=2005 |title=Species distinction in Irish populations of ''Quercus petraea'' and ''Q. robur'': Morphological versus molecular analyses |journal=Annals of Botany |pmid=16199484 |volume=96 |issue=7 |pages=1237–1246 |doi=10.1093/aob/mci275|pmc=4247074 }}</ref> The maintenance of particular loci for adaptation to ecological niches may explain the retention of species identity despite significant gene flow.<ref>{{Cite journal |last1=Zhang |first1=Ruhua |last2=Hipp |first2=Andrew L. |last3=Gailing |first3=Oliver |date= October 2015 |title=Sharing of chloroplast haplotypes among red oak species suggests interspecific gene flow between neighboring populations |journal=Botany |volume=93 |issue=10 |pages=691–700 |doi=10.1139/cjb-2014-0261 |issn=1916-2790 |hdl=1807/69792 |hdl-access=free}}</ref>

The [[Fagaceae]], or beech family, to which the oaks belong, is a slowly-evolving [[clade]] compared to other [[angiosperm]]s,<ref>{{Cite journal|doi=10.1139/g93-089 |last1=Frascaria |first1=N. |first2=L. |last2=Maggia |first3=M. |last3=Michaud |first4=J. |last4=Bousquet |year=1993 |title=The RBCL Gene Sequence from Chestnut Indicates a Slow Rate of Evolution in the Fagaceae |journal=Genome |volume=36 |issue=4 |pages=668–671 |pmid=8405983|url=http://agritrop.cirad.fr/590955/1/1993_frascaria%20et%20al.pdf }}</ref><ref>{{cite journal |last1=Manos |first1=P. S. |first2=A. M. |last2=Stanford |year=2001 |title=The historical biogeography of Fagaceae: Tracking the tertiary history of temperate and subtropical forests of the Northern Hemisphere |journal=International Journal of Plant Sciences |volume=162 |pages=S77–S93 |issue=Suppl. 6 |doi=10.1086/323280 |bibcode=2001IJPlS.162S..77M |s2cid=84936653 }}</ref> and the patterns of hybridization and introgression in ''Quercus'' pose a significant challenge to the [[species concept|concept of a species]] as a group of "actually or potentially interbreeding populations which are reproductively isolated from other such groups."<ref name="Raven 2005"/> 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.<ref name="Raven 2005">{{cite book |last1=Raven |first1=Peter H. |first2=George B. |last2=Johnson |first3=Jonathan B. |last3=Losos |first4=Susan R. |last4=Singer |title=Biology |url=https://archive.org/details/biology00pete |url-access=registration |edition=Seventh |publisher=McGraw Hill |location=New York |year=2005 |isbn=0-07-111182-4}}</ref>

=== Diseases and pests ===

[[File:Oak Mildew.JPG|thumb|Oak [[powdery mildew]] on pedunculate oak, caused by ''[[Erysiphe alphitoides]]'']]

Oaks are affected by a large number of pests and diseases. For instance, ''Q. robur'' and ''Q. petraea'' in Britain host 423 insect species.<ref name="Kennedy Southwood 1984">{{cite journal |last1=Kennedy |first1=Catherine E.J. |last2=Southwood |first2=T. Richard E. |year=1984 |title=The number of species of insect associated with British trees. A reanalysis |journal=[[Journal of Animal Ecology]] |volume=53 |issue=53 |pages=455–478 |jstor=4528 |doi=10.2307/4528|bibcode=1984JAnEc..53..455K }}</ref> This diversity includes 106 [[Macrolepidoptera|macro-moths]], 83 [[Microlepidoptera|micro-moths]], 67 [[beetle]]s, 53 [[cynipoidea]]n wasps, 38 [[heteroptera]]n bugs, 21 [[auchenorrhyncha]]n bugs, 17 [[sawfly|sawflies]], and 15 [[aphid]]s.<ref name="Kennedy Southwood 1984"/> The insect numbers are seasonal: in spring, chewing insects such as caterpillars become numerous, followed by insects with sucking mouthparts such as aphids, then by [[leaf miner]]s, and finally by gall wasps such as ''[[Neuroterus]]''.<ref>{{cite journal |last1=Southwood |first1=T. Richard E. |last2=Wint |first2=G.R. William |last3=Kennedy |first3=Catherine E.J. |last4=Greenwood |first4=Kennedy |year=2004 |title=Seasonality, abundance, species richness and specificity of the phytophagous guild of insects on oak (''Quercus'') canopies |journal=[[European Journal of Entomology]] |volume=101 |issue=101 |pages=43–50|doi=10.14411/eje.2004.011 |doi-access=free }}</ref> Several [[powdery mildew]]s affect oak species. In Europe, the species ''[[Erysiphe alphitoides]]'' is the most common.<ref>{{Cite journal |doi=10.1111/j.1439-0329.2008.00544.x |title=New insights into the identity and origin of the causal agent of oak powdery mildew in Europe |year=2008 |last1=Mougou |first1=A. |last2=Dutech |first2=C. |last3=Desprez-Loustau |first3=M.-L. |journal=Forest Pathology |volume=38 |issue=4 |page=275|bibcode=2008FoPat..38..275M }}</ref> It reduces the ability of leaves to photosynthesize, and infected leaves are shed early.<ref name="Hajji Dreyer 2009">{{Cite journal |title=Impact of ''Erysiphe alphitoides'' on transpiration and photosynthesis in ''Quercus robur'' leaves |year=2009|last1=Hajji |first1=M. |last2=Dreyer |first2=E. |last3=Marçais |first3=B. |journal=European Journal of Plant Pathology |volume=125 |issue=1 |pages=63–72 |doi=10.1007/s10658-009-9458-7 |bibcode=2009EJPP..125...63H |s2cid=21267431 |url=https://hal.archives-ouvertes.fr/hal-02103659/file/2009-EJPP-Hajji%26al.pdf}}</ref>
Another significant threat, the [[oak processionary]] moth (''Thaumetopoea processionea''), has emerged in the UK since 2006. 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.<ref name=forestry>{{cite web |author=unspecified |title=Oak Processionary Moth - Tree pests and diseases |website=[[Forestry Commission|Forestry Commission (UK)]] |url=https://www.forestry.gov.uk/oakprocessionarymoth |date=11 September 2018 |access-date=31 January 2019 |archive-date=20 November 2018 |archive-url=https://web.archive.org/web/20181120133817/https://www.forestry.gov.uk/oakprocessionarymoth |url-status=dead }}</ref> A little-understood disease of mature oaks, [[acute oak decline]], has affected the UK since 2009.<ref>{{cite news |last=Kinver |first=Mark |date=28 April 2010 |title=Oak disease 'threatens landscape' |work=BBC News |url=http://news.bbc.co.uk/2/hi/science_and_environment/10089581.stm |url-status=live |access-date=29 April 2010 |archive-url=https://web.archive.org/web/20100429031402/http://news.bbc.co.uk/2/hi/science_and_environment/10089581.stm |archive-date=29 April 2010}}</ref> 
In California, goldspotted oak borer (''[[Agrilus auroguttatus]]'') has destroyed many oak trees,<ref name="Coleman 2008">{{cite web |last=Coleman |first=T. W. |url=http://www.fs.fed.us/r5/spf/fhp/socal/CnfOakMortalityBE080408.pdf |title=New insect evidence in continuing oak mortality |publisher=US Forest Service |date=4 August 2008}}</ref> while sudden oak death, caused by the [[oomycete]] pathogen ''[[Phytophthora ramorum]]'', has devastated oaks in California and Oregon, and is present in Europe.<ref name="Scientific Societies 2008">{{cite journal |title=Sudden oak death, ramorum leaf blight, ramorum shoot blight |journal=The Plant Health Instructor |publisher=Scientific Societies |year=2008 |issn=1935-9411 |doi=10.1094/phi-i-2008-0227-01 |last1=Parke |first1=J.L. |last2=Peterson |first2=Ebba K.}}</ref> Japanese oak wilt, caused by the fungus ''[[Raffaelea quercivora]]'', has rapidly killed trees across Japan.<ref name="Kuroda Yamada 1996">{{cite journal |last1=Kuroda |first1=K. |last2=Yamada |first2=T. |year=1996 |title=Discoloration of sapwood and blockage of xylem sap ascent in the trunks of wilting ''Quercus'' spp. following attack by ''Platypus quercivorus'' |journal=Journal of the Japanese Forestry Society |volume=78 |issue=1 |pages=84–88 |url=http://ci.nii.ac.jp/naid/110002830776/en}}</ref>

=== Gall communities ===

{{further|Gall|Gall wasp}}

Many [[galls]] are found on oak leaves, buds, flowers, and roots. Examples are [[oak artichoke gall]], [[oak marble gall]], [[oak apple]] gall, [[knopper gall]], and [[Neurotus quercus-baccarum|spangle gall]]. These galls are the handiwork of tiny wasps from the  [[Cynipidae]]. In a complex ecological relationship, these gall wasps become hosts to [[parasitoid wasp]]s—primarily from the order [[Chalcidoidea]]—which lay their larvae inside the gall wasps, ultimately leading to the hosts' demise. Additionally, [[inquiline]]s live [[Commensalism|commensally]] within the galls without harming the gall wasps.<ref>{{cite journal |last1=Askew |first1=Richard R. |last2=Melika |first2=George |last3=Pujade-Villar |first3=Juli |last4=Schönrogge |first4=Karsten |last5=Stone |first5=Graham N. |last6=Nieves-Aldrey |first6=Jose Luis |title=Catalogue of parasitoids and inquilines in cynipid oak galls in the West Palaearctic |journal=Zootaxa |date=30 April 2013 |volume=3643 |issue=3643 |pages=1–133 |doi=10.11646/zootaxa.3643.1.1 |pmid=25340198 |isbn=978-1-77557-147-6 |url=https://www.researchgate.net/publication/237007745}}</ref>

<gallery mode=packed>
File:Gallrazorback.jpg|Oak apple gall on ''[[Quercus garryana]]''
File:Oak apples on oak leaf and in cross section.JPG|Oak apples on oak leaf
File:Biorhiza pallida male.jpg|''[[Biorhiza pallida]]'' male, the cause of oak apple galls
</gallery>

== Toxicity ==

The leaves and acorns of oaks are poisonous to [[livestock]], including [[cattle]] and [[horse]]s, if eaten in large amounts, due to the toxin [[tannic acid]], which causes kidney damage and [[gastroenteritis]].<ref>{{cite journal |last=Dun |first=Kath |title=Oak poisoning in cattle |journal=UK Vet Livestock |volume=11 |issue=5 |year=2006 |pages=47–50 |doi=10.1111/j.2044-3870.2006.tb00047.x }}</ref><ref name="Smith Naylor Knowles Mair 2014">{{cite journal |last1=Smith |first1=S. |last2=Naylor |first2=R. J. |last3=Knowles |first3=E. J. |last4=Mair |first4=T. S. |last5=Cahalan |first5=S. D. |last6=Fews |first6=D. |last7=Dunkel |first7=B. |title=Suspected acorn toxicity in nine horses |journal=Equine Veterinary Journal |publisher=Wiley |volume=47 |issue=5 |date=7 October 2014 |doi=10.1111/evj.12306 |pages=568–572|pmid=24917312 |url=http://researchonline.rvc.ac.uk/id/eprint/9469/ }}</ref> An exception is the [[domestic pig]], which, under the right conditions, may be fed entirely on acorns,<ref>Cappai, Maria Grazia, et al. "Pigs use endogenous proline to cope with acorn (''Quercus pubescens'' Willd.) combined diets high in hydrolysable tannins." Livestock Science 155.2-3 (2013): 316–322.</ref> and has traditionally been pastured in oak woodlands (such as the Spanish ''[[dehesa (pastoral management)|dehesa]]''<ref>Joffre, R; Rambal, S.; Ratte, J.P. (1999). "The dehesa system of southern Spain and Portugal as a natural ecosystem mimic," ''[[Journal of Agroforestry]]'' 45(1-3): 57-79.</ref> and the English system of [[pannage]]).<ref>{{cite book |last=Kreiner |first=Jamie |url=https://www.jstor.org/stable/j.ctv177tk45 |title=Legions of Pigs in the Early Medieval West |publisher=Yale University Press |year=2020 |isbn=978-0-3002-4629-2 |location=New Haven |pages=108–119 |doi=10.2307/j.ctv177tk45 |jstor=j.ctv177tk45 |url-access=subscription}}</ref> Humans can eat acorns after [[leaching (chemistry)|leaching]] out the tannins in water.<ref>{{citation |last=Bainbridge |first=D. A. |title=Use of acorns for food in California: past, present and future |date=12–14 November 1986 |url=http://www.ecocomposite.org/native/UseOfAcornsForFoodInCalifornia.doc |archive-url=https://web.archive.org/web/20101027113825/http://ecocomposite.org/native/UseOfAcornsForFoodInCalifornia.doc |location=San Luis Obispo, CA. |publisher=Symposium on Multiple-use Management of California's Hardwoods |access-date=11 July 2015 |archive-date=27 October 2010 |url-status=dead}}</ref>

== Uses ==

=== Timber ===

[[File:Charpente eglise Saint-Girons Monein.jpg|thumb|upright|Heart of oak [[Beam (structure)|beams]] of the frame of the [[Église Saint-Girons]] in [[Monein]], France]]

Oak timber is a strong and hard wood with many uses, such as for [[furniture]], floors, building frames, and [[Wood veneer|veneer]]s.<ref>{{cite web |last1=Dotson |first1=J. Dianne |title=What Are Oak Trees Used for? |url=https://sciencing.com/kamani-wood-8516541.html |website=Sciencing |access-date=9 October 2023 |date=22 November 2019}}</ref> The wood of ''[[Quercus cerris]]'' (the Turkey oak) has better mechanical properties than those of the white oaks ''[[Quercus petraea|Q.&nbsp;petraea]]'' and ''[[Quercus robur|Q.&nbsp;robur]]''; the heartwood and sapwood have similar [[strength of materials|mechanical properties]].<ref>Merela, Maks, and Katarina Čufar. "[https://www.researchgate.net/profile/Maks-Merela/publication/272905935_Density_and_Mechanical_Properties_of_Oak_Sapwood_Versus_Heartwood/links/577e29bd08aeaa6988b0920b/Density-and-Mechanical-Properties-of-Oak-Sapwood-Versus-Heartwood.pdf Density and mechanical properties of oak sapwood versus heartwood in three different oak species]". ''Drvna industrija'' 64.4 (2013): 323–334.</ref> Of the North American red oaks, the [[northern red oak]], ''Quercus rubra'', is highly prized for lumber.<ref>Aldrich, Preston R., et al. "Whole-tree silvic identifications and the microsatellite genetic structure of a red oak species complex in an Indiana old-growth forest." Canadian Journal of Forest Research 33.11 (2003): 2228–2237.</ref><ref>{{eFloras|1|233501082|Quercus shumardii |first=Kevin C. |last=Nixon |volume=3}}</ref>
The wood is resistant to insect and fungal attack.<ref>Thaler, Nejc; Humar, Miha. "[https://www.sciencedirect.com/science/article/pii/S0964830513003168 Performance of oak, beech and spruce beams after more than 100 years in service]". ''International Biodeterioration & Biodegradation'' 85 (2013): 305–310.</ref>

Wood from ''Q.&nbsp;robur'' and ''Q.&nbsp;petraea'' was used in Europe for [[shipbuilding]], especially of naval [[man-of-war|men of war]], until the 19th century.<ref>{{cite book |last=Baugh |first=Daniel A. |title=British Naval Administration in the Age of Walpole |url=https://archive.org/details/britishnavaladmi0000baug |url-access=registration |year=1965 |page=[https://archive.org/details/britishnavaladmi0000baug/page/242 242] |publisher=Princeton University Press |oclc=610026758}}</ref> In hill states of India such as [[Uttarakhand]], along with being used for fuelwood and timber, oak wood is used for [[agricultural implement]]s, while the leaves serve as [[fodder]] for livestock during lean periods.<ref>[[Chandra Prakash Kala|Kala, C.P.]] (2004). Studies on the indigenous knowledge, practices, and traditional uses of forest products by human societies in Uttarakhand state of India. GBPIHED, Almora, India</ref><ref>Kala, C.P. (2010). ''Medicinal Plants of Uttarakhand: Diversity Livelihood and Conservation''. BioTech Books, Delhi, {{ISBN|8176222097}}.</ref>

=== Other traditional products ===

[[Oak bark]], with its high tannin content, was traditionally used in the Old World for [[Tanning (leather)|tanning]] [[leather]].<ref>Clarkson, L. A. "The English bark trade, 1660–1830" ''The Agricultural History Review'' 22.2 (1974): 136–152. {{JSTOR|40273608}}</ref> Oak [[gall]]s were used for centuries as a main ingredient in [[iron gall ink]] for manuscripts, harvested at a specific time of year.<ref>{{Cite web|url=https://www.historytoday.com/history-matters/history-ink-six-objects|title=A History of Ink in Six Objects|website=History Today}}</ref> In Korea, [[sawtooth oak]] bark is used to make [[Roof shingle|shingles]] for [[Traditional Korean roof construction|traditional roof construction]].<ref name="Jeon 2016">{{cite book |last=Jeon |first=BongHee |title=A Cultural History of the Korean House |date=2016 |publisher=Seoul Selection |location=Seoul |isbn=978-89-97639-63-2 |page=49 |url=https://www.aks.ac.kr/ikorea/upload/intl/korean/UserFiles/UKS5_Korean_House_eng.pdf |chapter=3: Hanok: The Formation of the Traditional Korean House |quote=The gulpijip (oak-bark-roofed house) and neowajip (shingled house) are found in the northeastern part of the Korean peninsula, as well as in Korea’s more mountainous areas. ... Gulpijip uses roofing made with the bark of trees such as cone-fruit platycarya, [[sawtooth oak]], and cedar, which all have relatively thick bark.}}</ref> The dried bark of the white oak was used in [[traditional medicine|traditional medical preparations]]; its tannic acid content made it astringent and antiseptic.<ref>Henkel, Alice. [https://books.google.com/books?id=lpUUAAAAYAAJ American medicinal barks]. No. 139. US Government Printing Office, 1909.</ref> Acorns have been ground to make a flour,<ref>Szabłowska, Emilia; Tańska, Małgorzata. "Acorn flour properties depending on the production method and laboratory baking test results: A review." Comprehensive Reviews in Food Science and Food Safety 20.1 (2021): 980-1008.</ref> and roasted for acorn coffee.<ref>{{cite journal |last=Samsonowicz |first=Mariola |display-authors=etal |title=Antioxidant properties of coffee substitutes rich in polyphenols and minerals |journal=Food Chemistry |issue=278 |year=2019 |volume=278 |pages=101–109|doi=10.1016/j.foodchem.2018.11.057 |pmid=30583350 |s2cid=58542098 }}</ref>

=== Culinary ===

[[Barrel (storage)|Barrels]] for [[Aging barrel|aging]] wines, [[sherry]], and spirits such as [[brandy]] and [[Scotch whisky]] are made from oak, with [[single barrel whiskey|single barrel malt whiskies]] fetching a premium.<ref name="Piggott 2003">Piggott, John R.; Conner, John M. "Whiskies." Fermented beverage production. Boston, Massachusetts: Springer, 2003. 239–262.</ref> The use of [[oak (wine)|oak in wine]] adds a range of flavours. Oak barrels, which may be charred before use, contribute to their contents' colour, taste, and aroma, imparting a desirable oaky [[vanillin]] flavour. A dilemma for wine producers is to choose between French and American oakwoods. French oaks (''Quercus robur'', ''Q.&nbsp;petraea'') give greater refinement and are chosen for the best, most expensive wines. American oak contributes greater texture and resistance to ageing, but produces a more powerful bouquet.<ref>Pérez-Prieto, Luis J., et al. "Extraction and formation dynamic of oak-related volatile compounds from different volume barrels to wine and their behavior during bottle storage." Journal of Agricultural and Food Chemistry 51.18 (2003): 5444–5449.</ref><ref>Perez‐Prieto, Luis Javier, et al. "Oak‐matured wines: influence of the characteristics of the barrel on wine colour and sensory characteristics." Journal of the Science of Food and Agriculture 83.14 (2003): 1445–1450.</ref>

Oak wood chips are used for [[smoking (cooking)|smoking]] foods such as fish, meat, and [[cheese]].<ref name="Varlet Prost Serot 2007">{{cite journal |last1=Varlet |first1=Vincent |last2=Prost |first2=Carole |last3=Serot |first3=Thierry |title=Volatile aldehydes in smoked fish: Analysis methods, {{as written|occur|rence [sic]}} and mechanisms of formation |journal=Food Chemistry |publisher=Elsevier BV |volume=105 |issue=4 |year=2007 |issn=0308-8146 |doi=10.1016/j.foodchem.2007.03.041 |pages=1536–1556}}</ref><ref>{{cite journal |last1=Guillén |first1=Marı́a D. |first2=Manzanos |last2=Marı́a J. |title=Study of the volatile composition of an aqueous oak smoke preparation |journal=Food Chemistry |volume=79 |issue=3 |year=2002 |pages=283–292|doi=10.1016/S0308-8146(02)00141-3 }}</ref> 
In Japan, [[Children's Day]] is celebrated with {{transliteration|ja|[[Kashiwa-mochi]]}} rice cakes, filled with a sweet red bean paste, and wrapped in a {{transliteration|ja|kashiwa}} oak leaf.<ref>{{cite web |url=http://www.travel-around-japan.com/j54-confectionery.html |title=Japanese confectionery |website=Travel Around Japan |access-date=27 September 2024}}</ref>
The bark of the [[cork oak]] is used to produce cork stoppers for [[wine]] bottles. This species grows around the [[Mediterranean Sea]]; [[Portugal]], [[Spain]], [[Algeria]], and [[Morocco]] produce most of the world's supply.<ref name="Amorim">{{cite web |title=Mitos e curiosidades |url=https://www.amorim.com/a-cortica/mitos-e-curiosidades/Quanto-tempo-vive-um-sobreiro/110/400/ |publisher=[[Corticeira Amorim|Amorim]] |access-date=13 February 2021}}</ref>

Acorns of various oak species have been used as food for millennia, in Asia, Europe, the Middle East, North Africa, and among the native peoples of North America. In North Africa, acorns have been pressed to make acorn oil: the [[cooking oil|oil]] content can be as high as 30%. Oaks have also been used as [[fodder]], both leaves and acorns being fed to livestock such as pigs. Given their high tannin content, acorns have often been leached to remove tannins before use as fodder.<ref>{{cite journal |last1=Bainbridge |first1=David A. |title=1 Use of Acorns for Food in California: Past, Present, Future |journal=1 Use of Acorns for Food in California: Past, Present, Future David A. Bainbridge, Dry Lands Research Institute, University of California, Riverside, CA 92521 Proceedings of the Symposium on Multiple-use Management of California's Hardwoods, November 12-14, 1986, San Luis Obispo, California |date=1986 |pages=453–458 |url=https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=f2e579544c5078e581b28acb81396811d6ae7827}}</ref>

<gallery class=center mode=nolines widths=200px heights=200px>
File:Sherry cellar, Solera system, 2003.jpg|[[Sherry]] maturing in [[barrel (storage)|oak barrels]] 
File:Cork oak trunk section.jpg|A cross section of the trunk of a [[cork oak]], ''[[Quercus suber]]'', showing the thick spongy bark used for making wine bottle corks
File:Kashiwa-mochi.jpg|[[Kashiwa-mochi]] rice cake wrapped in oak leaf, Japan
</gallery>

== Conservation ==

An estimated 31% of the world's oak species are threatened with extinction, while 41% of oak species are considered to be of [[conservation status|conservation concern]]. The countries with the highest numbers of threatened oak species (as of 2020) are China with 36 species, Mexico with 32 species, Vietnam with 20 species, and the US with 16 species. Leading causes are [[climate change]] and [[Invasive species|invasive pests]] in the US, and [[deforestation]] and [[urbanization]] in Asia.<ref>{{Cite web |title=The Red List of Oaks 2020 |url=https://globaltrees.org/wp-content/uploads/2021/01/Oaks2020HR.pdf |website=Global Trees Campaign |access-date=2020-12-13 |url-status=dead |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716045545/https://globaltrees.org/wp-content/uploads/2021/01/Oaks2020HR.pdf}}</ref><ref>{{Cite web |title=One-third of the world's oaks at risk of extinction, according to new BGCI report |url=https://www.bgci.org/news-events/red-list-of-oaks-2020/ |access-date=2020-12-13 |website=Botanic Gardens Conservation International }}</ref><ref>{{Citation |last1=Carrero |first1=Christina |last2=Jerome |first2=Diana |last3=Beckman |first3=Emily |last4=Byrne |first4=Amy |last5=Coombes |first5=Allen J. |last6=Deng |first6=Min |last7=González Rodríguez |first7=Antonio |last8=Sam |first8=Hoang Van |last9=Khoo |first9=Eyen |last10=Nguyen |first10=Ngoc |last11=Robiansyah |first11=Iyan |last12=Rodríguez Correa |first12=Hernando |last13=Sang |first13=Julia |last14=Song |first14=Yi-Gang |last15=Strijk |first15=Joeri |last16=Sugau |first16=John |last17=Sun |first17=Weibang |last18=Valencia-Ávalos |first18=Susana |last19=Westwood |first19=Murphy |display-authors=5 |date=2020 |title=The Red List of Oaks 2020 |publication-place=Lisle, IL |publisher=The Morton Arboretum |url=https://static1.squarespace.com/static/557dec57e4b0c3993deb6044/t/60ba66607de08b6cc5e42d00/1622828642301/RedListOaks2020.pdf }}</ref> 
In the Himalayan region of India, oak forests are being invaded by [[pine]] trees due to global warming. The associated pine forest species may cross frontiers and integrate into the oak forests.<ref>Kala, C.P. (2012). ''Biodiversity, communities and climate change''. Teri Publications, New Delhi, {{ISBN|817993442X}}.</ref> 
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 plantation]]s and [[cattle ranching]]. There is a continuing threat to these forests from exploitation for timber, fuelwood, and [[charcoal]].<ref>Kappelle, M. (2006). "Neotropical montane oak forests: overview and outlook", pp 449–467 in: Kappelle, M. (ed.). ''Ecology and conservation of neotropical montane oak forests''. Ecological Studies No. 185. Springer-Verlag, Berlin, {{doi|10.1007/3-540-28909-7_34}} {{ISBN|978-3-540-28908-1}}.</ref> 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.<ref>Lorimer, C.G. (2003) [http://www.aibs.org/bioscience-editorials/editorial_2003_10.html Editorial: The decline of oak forests] {{webarchive|url=https://web.archive.org/web/20140317194907/http://www.aibs.org/bioscience-editorials/editorial_2003_10.html |date=17 March 2014 }}. American Institute of Biological Sciences.</ref> However, disturbance-tolerant oaks may have benefited from grazers like [[American bison|bison]], and suffered when the bison were removed following [[European colonization of the Americas|European colonization]].<ref name="Hitchmough Vera 2002">{{cite journal | last1=Hitchmough | first1=James | last2=Vera | first2=F. W. M. | title=Grazing Ecology and Forest History | journal=Garden History | volume=30 | issue=2 | year=2002 | issn=0307-1243 | doi=10.2307/1587257 | page=263| jstor=1587257 }}</ref><ref>{{cite book |last=Carpenter |first=Paul |title=Plants in the Landscape |publisher=W.H. Freeman and Company |year=1990 |isbn=0716718081 |location=New York |page=73}}</ref>

==Culture==

=== Symbols ===

[[File:Coat of arms of Estonia.svg|thumb|upright|The oak features in many coats of arms, such as [[Coat of arms of Estonia|that of Estonia]].<ref name="Estonian Institute">{{cite web |last=Estonian Institute |title=National symbols of Estonia |url=http://www.estinst.ee/publications/symbols/ |publisher=Estonian Institute |access-date=4 January 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120114085551/http://www.estinst.ee/publications/symbols/ |archive-date=14 January 2012}}</ref> ]]

The oak is a widely used symbol of strength and [[endurance]].<ref name="Leroy Plomion Kremer 2019">{{cite journal | last1=Leroy | first1=Thibault | last2=Plomion | first2=Christophe | last3=Kremer | first3=Antoine | title=Oak symbolism in the light of genomics | journal=New Phytologist | publisher=Wiley | volume=226 | issue=4 | date=25 July 2019 | issn=0028-646X | doi=10.1111/nph.15987 | pages=1012–1017| pmid=31183874 | pmc=7166128 }}</ref> It is the [[national tree]] of many countries,<ref name="Venables 2012"/> including the US,<ref>{{cite web |url=http://www.arborday.org |title=Trees – Arbor Day Foundation |publisher=Arborday.org |access-date=27 April 2010 |url-status=live |archive-url=https://web.archive.org/web/20100428143334/http://www.arborday.org/ |archive-date=28 April 2010}}</ref> [[Bulgaria]], [[Croatia]], [[Cyprus]] ([[Quercus alnifolia|golden oak]]), [[Estonia]], [[France]], [[Germany]], [[Moldova]], [[Jordan]], [[Latvia]], [[Lithuania]], [[Poland]], [[Romania]], [[Serbia]], and [[Wales]].<ref name="Venables 2012">{{cite web |title=Oak as a Symbol |url=http://www.venablesoak.co.uk/about-oak/oak-as-a-symbol-2/|work=Venables Oak |access-date=26 September 2012 |url-status=dead |archive-url=https://web.archive.org/web/20130505014026/http://www.venablesoak.co.uk/about-oak/oak-as-a-symbol-2/ |archive-date=5 May 2013}}</ref> Ireland's fifth-largest city, [[Derry]], is named for the tree, from {{Irish place name|Doire|oak}}.<ref>{{cite web |title=Derry |url=https://www.etymonline.com/word/derry |website=Etymology Online |access-date=9 October 2023}}</ref>  Oak branches are displayed on some German coins, both of the former [[Deutsche Mark]] and the [[euro]].<ref>{{Cite book |last=Schierz |first=Kai Uwe |chapter=Von Bonifatius bis Beuys, oder: Vom Umgang mit heiligen Eichen |title=Bonifatius: Heidenopfer, Christuskreuz, Eichenkult |trans-title=Boniface: Heathen Sacrifice, Christ's Cross, Oak Cult |year=2004 |publisher=Stadtverwaltung Erfurt |pages=139–145 |editor=Hardy Eidam |editor2=Marina Moritz |editor3=Gerd-Rainer Riedel |editor4=Kai-Uwe Schierz |language=de }}</ref>
Oak leaves symbolize [[military rank|rank]] in armed forces including those [[United States Armed Forces|of the United States]]. Arrangements of oak leaves, acorns, and sprigs indicate different branches of the [[United States Navy staff corps]] officers.<ref name="Websters Online Dictionary">{{cite web |title=Political or Symbolic |url=http://www.websters-online-dictionary.org/definitions/oak |work=Extended Definition: oak |access-date=26 September 2012 |url-status=dead|archive-url=https://web.archive.org/web/20130530214714/http://www.websters-online-dictionary.org/definitions/oak |archive-date=30 May 2013}}</ref><ref>{{Cite web|url=http://ar670.com/articles/view/29/wear-of-appurtenances/311 |title=Army Regulation 670-1 {{!}} Wear of appurtenances {{!}} Section 29.12 Page 278 |website=ar670.com |archive-url=https://web.archive.org/web/20180122161840/http://ar670.com/articles/view/29/wear-of-appurtenances/311 |archive-date=22 January 2018 |url-status=dead |access-date=2018-01-19}}</ref> The oak tree is used as a symbol by several political parties and organisations. It is the symbol of the [[Conservative Party (UK)|Conservative Party]] in the [[United Kingdom]],<ref>{{cite news |last=Glover |first=Julian |title=Thatcher's torch extinguished as Cameron's Conservatives carve new logo out of oak |url=https://www.theguardian.com/politics/2006/aug/09/conservatives.marketingandpr |access-date=9 October 2023 |work=[[The Guardian]] |date=9 August 2006}}</ref> and formerly of the [[Progressive Democrats]] in [[Republic of Ireland|Ireland]].<ref name=r9>[https://web.archive.org/web/20071119201140/http://www.progressivedemocrats.ie/about_us/coalition_government_1989_to_1992/ Coalition Government 1989 To 1992]. progressivedemocrats.ie</ref>

=== Religion ===

[[File:Grīdnieku dižozols.JPG|thumb|Grīdnieku ancient oak in Rumbas parish, [[Latvia]], girth {{convert|8.27|m|ft}} 2015]]

The prehistoric [[Proto-Indo-Europeans|Indo-European]] tribes worshipped the oak and connected it with a [[thunder god]], and this tradition descended to many classical cultures. In [[Greek mythology]], the oak is the tree sacred to [[Zeus]], king of the gods. In Zeus's [[oracle]] in [[Dodona]], [[Epirus]], the sacred oak was the centerpiece of the precinct, and the priests would [[divination|divine]] the pronouncements of the god by interpreting the rustling of the oak's leaves.<ref>Frazer, James George (1922). [http://www.bartleby.com/196/26.html ''The Golden Bough''. Chapter XV: The Worship of the Oak.] {{webarchive|url=https://web.archive.org/web/20120521225940/http://www.bartleby.com/196/26.html |date=21 May 2012 }}</ref> Mortals who destroyed such trees were said to be punished by the gods since the ancient Greeks believed beings called [[hamadryad]]s inhabited them.<ref name="Bell1790">{{cite book |author=[[John Bell (publisher)|Bell, John]] |title=Bell's New Pantheon; Or, Historical Dictionary of the Gods, Demi-gods, Heroes, and Fabulous Personages of Antiquity: Also, of the Images and Idols Adored in the Pagan World; Together with Their Temples, Priests, Altars, Oracles, Fasts, Festivals, Games ... |url=https://archive.org/details/bellsnewpantheo00bellgoog |year=1790 |publisher=J. Bell |pages=[https://archive.org/details/bellsnewpantheo00bellgoog/page/n376 366]–7}}</ref> In [[Norse mythology|Norse]] and [[Baltic mythology]], the oak was sacred to the thunder gods [[Thor]] and [[Perkūnas]] respectively.<ref>{{cite book |title=Suomen terveyskasvit: luonnon parantavat yrtit ja niiden salaisuudet |page=256 |author=Marja-Leena Huovinen & Kaarina Kanerva |year=1982 |location=Helsinki |publisher=Valitut Palat |isbn=951-9078-87-8 | language=fi}}</ref><ref>{{cite web |title=Ąžuolas paprastasis |url=https://gamtininkas.lt/augalai/azuolas-paprastasis-lot-quercus-robur-l/ |date=21 February 2011 |website=Zolininkas.lt |language=lt-LT |access-date=10 January 2018}}</ref> In [[Celtic polytheism]], the name [[druid]], Celtic priest, is connected to Proto-Indo-European ''*deru'', meaning oak or tree.<ref name=Credo>{{cite book |last=Ferber |first=Michael |chapter=Oak |title=A Dictionary of Literary Symbols |publisher=Cambridge University Press |year=2017 |edition=3rd |isbn=978-1-1071-7211-1}}</ref> Veneration of the oak survives in [[Serbian Orthodox Church]] tradition. [[Christmas]] celebrations include the [[Badnjak (Serbian)|''badnjak'']], a branch taken from a young and straight oak ceremonially felled early on Christmas Eve morning, similar to a [[yule log]].<ref>{{cite web |title=Fight to save 'sacred' oak from road |url=https://www.bbc.com/news/blogs-news-from-elsewhere-33326394 |publisher=BBC |date=30 June 2015}}</ref>

=== History ===

{{main|List of individual trees}}
: Category: [[:Category:Individual oak trees|''Individual oak trees'']]

Several oak trees hold cultural importance; such as the [[Royal Oak (tree)|Royal Oak]] in Britain,<ref>{{cite web |title=Oak mythology and folklore |url=https://treesforlife.org.uk/into-the-forest/trees-plants-animals/trees/oak/oak-mythology-and-folklore/ |website=Trees for Life |access-date=29 September 2023}}</ref> the [[Charter Oak]] in the United States,<ref>{{cite web |date=2014-04-23 |title=The Legend of the Charter Oak |url=https://www.newenglandhistoricalsociety.com/legend-charter-oak/ |access-date=2021-04-23 |website=New England Historical Society |archive-date=2021-04-23 |archive-url=https://web.archive.org/web/20210423002123/https://www.newenglandhistoricalsociety.com/legend-charter-oak/ |url-status=live }}</ref> and the [[Guernica oak]] in the [[Basque Country (greater region)|Basque Country]].<ref name="ElMundoTrees">{{cite news |author=unspecified |title=Otro árbol de Gernika |newspaper=[[El Mundo (Spain)|El Mundo]] |date=26 February 2005}}</ref> "[[The Proscribed Royalist, 1651]]", a famous painting by [[John Everett Millais]], depicts a [[Royalist]] hiding in an oak tree while fleeing from [[Oliver Cromwell|Cromwell's]] forces.<ref>[http://www.arborecology.co.uk/article_ancient_tree.htm Arborecology, containing a photograph of the Millais oak] {{webarchive|url=https://web.archive.org/web/20080828000601/http://www.arborecology.co.uk/article_ancient_tree.htm |date=28 August 2008 }}. arborecology.co.uk</ref><ref>Millais, J. G. (1899) [https://archive.org/details/lifelettersofsir01milliala ''Life and Letters of Sir John Everett Millais''], vol. 1, p. 166, London : Methuen.</ref>

In the [[Roman Republic]], a crown of oak leaves was given to those who had saved the life of a citizen in battle; it was called the "[[Civic Crown]]".<ref name="Credo"/> In his 17th century poem ''[[The Garden (poem)|The Garden]]'', [[Andrew Marvell]] critiqued the desire to be awarded such a leafy crown: "How vainly men themselves amaze / To win the [[Arecaceae|palm]], the oak, or [[Laurel wreath|bays]]; And their uncessant labors see / Crowned from some single herb or tree, ..."<ref>{{cite web |last=Marvell |first=Andrew |author-link=Andrew Marvell |title=The Garden |url=https://poets.org/poem/garden |website=Poets.org |access-date=29 September 2023}}</ref><ref>{{cite journal |last=Summers |first=Joseph H. |title=Reading Marvell's 'Garden' |journal=The Centennial Review |volume=13 |issue=1 |year=1969 |pages=18–37 |jstor=23738134 |quote=Hortus, Marvell's Latin poem which seems to be an earlier version of the English one ... both poems begin with the rejection of the worlds of ambitious action, urban life and passionate love, and celebrate a supposed entrance into an entirely new life within the garden.}}</ref>

== Notes ==

{{notelist}}

== References ==

{{reflist|30em}}

== Further reading ==

* Byfield, Liz (1990) ''An Oak Tree'', Collins Book Bus, London: Collins Educational, {{ISBN|0-00-313526-8}}
* [[Roger Phillips (photographer)|Phillips, Roger]] (1979). ''Trees of North America and Europe'', Random House, New York {{ISBN|0-394-50259-0}}.
* Logan, William B. (2005) ''Oak: The Frame of Civilization'', New York; London: W. W. Norton, {{ISBN|0-393-04773-3}}
* Paterson, R. T. (1993). ''Use of Trees by Livestock'', '''5''': ''Quercus'', Chatham: Natural Resources Institute, {{ISBN|0-85954-365-X}}
* Royston, Angela (2000). ''Life Cycle of an Oak Tree'', Heinemann first library, Oxford: Heinemann Library, {{ISBN|0-431-08391-6}}
* Savage, Stephen (1994). ''Oak Tree'', Observing nature series, Hove: Wayland, {{ISBN|0-7502-1196-2}}
* [[Arthur Tansley|Tansley, Arthur G.]] (1952). ''Oaks and Oak Woods'', Field study books, London: Methuen. {{OCLC|3196286}}.
* [[Marek Żukow-Karczewski|Żukow-Karczewski, Marek]] (1988). "Dąb – król polskich drzew" ("Oak – the king of the Polish trees"), ''AURA: A Monthly for the Protection and Shaping of Human Environment'', 9, 20–21.

== External links ==

{{Commons category|Quercus}}
{{Wikispecies|Quercus}}

* [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=108828 ''Flora of China'' – ''Cyclobalanopsis'']
* [http://extension.uga.edu/publications/detail.cfm?number=B1286 Oak diseases]
* [http://rbg-web2.rbge.org.uk/cgi-bin/nph-readbtree.pl/feout?FAMILY_XREF=&GENUS_XREF=Quercus&SPECIES_XREF=&TAXON_NAME_XREF=&RANK= Flora Europaea: ''Quercus'']
* [http://ufdc.ufl.edu/IR00001806/00001 Common Oaks of Florida]
* [http://oaksoftheworld.fr/ Oaks of the world]
* [https://web.archive.org/web/20120606034357/http://www.bgci.org/ourwork/oaksmain/ The Global Trees Campaign] The Red List of Oaks and Global Survey of Threatened Quercus
* {{cite EB1911 |wstitle=Oak |volume=19 |short=1 |pages=931–935}}
{{Culinary wrappings}}
{{Tannin source}}
{{Woodworking}}
{{Taxonbar|from=Q12004}}
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[[Category:Quercus| ]]
[[Category:Quercus taxa by common names|01]]
[[Category:Pseudocereals]]
[[Category:Wood]]
[[Category:Taxa named by Carl Linnaeus]]