An oak is a tree or shrub in the genus Quercus (; Latin "oak tree"), of which about 600 species exist on earth. "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 cold latitudes to tropical Asia and the Americas.
Oaks have spirally arranged leaves, with a lobed margin in many species; some have serrated leaves or entire leaves with a smooth margin. The flowers are catkins, produced in spring. The fruit is a nut called an acorn, 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 species. The live oaks are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.
Classification
Oak trees are
flowering plants. The genus is divided into two
subgenera and a number of
sections:
Subgenus Quercus
The Subgenus
Quercus is divided into the following sections:
Sect. Quercus (synonyms Lepidobalanus and Leucobalanus), the white oaks of Europe, Asia and North America. Styles are short; acorns mature in 6 months and taste sweet or slightly bitter; the inside of acorn shell is hairless. The leaves mostly lack a bristle on their lobe tips, which are usually rounded.
Sect. Mesobalanus, Hungarian oak and its relatives of Europe and Asia. Styles long; acorns mature in about 6 months and taste bitter; the inside of acorn shell is hairless. The section Mesobalanus is closely related to section Quercus and sometimes included in it.
Sect. Cerris, the Turkey oak and its relatives of Europe and Asia. Styles long; acorns mature in 18 months and taste very bitter. The inside of the acorn shell is hairless. Its leaves typically have sharp lobe tips, with bristles at the lobe tip.
Sect. Protobalanus, the Canyon live oak and its relatives, in southwest United States and northwest Mexico. Styles short, acorns mature in 18 months and taste very bitter. The inside of the acorn shell appears woolly. Leaves typically have sharp lobe tips, with bristles at the lobe tip.
Sect. Lobatae (synonym Erythrobalanus), the red oaks of North America, Central America and northern South America. Styles long, 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. Leaves typically have sharp lobe tips, with spiny bristles at the lobe.
Subgenus Cyclobalanopsis
The ring-cupped oaks of eastern and southeastern Asia. Evergreen trees growing 10–40 m 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. The Flora of China treats Cyclobalanopsis as a distinct genus, but most taxonomists consider it a subgenus of Quercus. It contains about 150 species.
× Q. muhlenbergii]]
Hybridisation
Interspecific hybridisation is quite common among oaks, but usually only between species within the same section and most common in the white oak group (subgenus
Quercus, section
Quercus; see
List of Quercus species). Inter-section hybrids, except between species of sections
Quercus and
Mesobalanus, are unknown. Recent systematic studies appear to confirm a high tendency of
Quercus species to hybridize because of a combination of factors. White oaks are unable to discriminate against pollination by other species in the same section because they are
wind pollinated and they have weak internal barriers to hybridisation, 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.
Frequent hybridisation among oaks has consequences for oak populations around the world; most notably, hybridization has produced large populations of hybrids with copious amounts of introgression, and the evolution of new species. Frequent hybridisation and high levels of introgression have caused different species in the same populations to share up to 50% of their genetic information. The high rates of hybridisation and introgression, produces genetic data that often does not differentiate between two clearly morphologically distinct species, but instead differentiates populations. Numerous hypotheses have been proposed to explain how oak species are able to remain morphologically and ecologically distinct with such high levels of gene flow, but the problem is still largely a mystery to botanists.
The Fagaceae, or oak family, is a very slowly evolving clade compared to other angiosperms, and the hybridisation patterns in Quercus pose a great challenge to the concept of a species. A species is often defined as a group of “actually or potentially interbreeding populations which are reproductively isolated from other such groups.” By this definition, many species of Quercus would be lumped together according to their geographic and ecological habitat, despite clear distinctions in morphology and, to a large extent, genetic data.
Uses
of the frame of Saint-Girons church in
Monein, France]]
Oak wood has a density of about 0.75 g/cm³, great strength and hardness, and is very resistant to insect and fungal attack because of its high
tannin content. It also has very attractive grain markings, particularly when
quartersawn. Wide, quarter-sawn boards of oak have been prized since the
Middle Ages for use in interior paneling of prestigious buildings such as the debating chamber of the
House of Commons in
London,
England, and in the construction of fine furniture. Oak wood, from
Quercus robur and
Quercus petraea, was used in Europe for the construction of
ships, especially naval
men of war, until the 19th century, and was the principal timber used in the construction of European
timber-framed buildings. Today oak
wood is still commonly used for
furniture making and flooring, timber frame buildings, and for veneer production.
Barrels in which red
wines,
sherry,
brandy and spirits such as
Scotch whisky and
Bourbon whiskey are
aged are made from European and American oak. The use of
oak in wine can add many different dimensions to wine based on the type and style of the oak. Oak barrels, which may be charred before use, contribute to the colour, taste, and aroma, of the contents, imparting a desirable oaky
vanillin flavour to these drinks. The great dilemma for wine producers is to choose between French and American oakwoods. French oaks (
Quercus robur,
Q. petraea) give the wine greater refinement and are chosen for best wines since they increase the price compared to those aged in American oak wood. American oak contributes greater texture and resistance to ageing, but produces more violent wine bouquets. and other foods.
maturing in
oak barrels]]
Japanese oak is used in the making of professional drums from manufacturer Yamaha Drums. The higher density of oak gives the drum a brighter and louder tone compared to traditional drum materials such as maple and birch.
, Quercus suber]]
The bark of Quercus suber, or Cork oak, is used to produce wine stoppers (corks). This species grows in the Mediterranean Sea region, with Portugal, Spain, Algeria and Morocco producing most of the world's supply. Of the North American oaks, the Northern red oak Quercus rubra is the most prized of the red oak group for lumber, all of which is marketed as red oak regardless of the species of origin. It is not good for outdoor use due to the open capillaries. One can blow air through an end grain piece 10 inches long to make bubbles come out in a glass of water. These opening give fungus easy access when the finish deteriorates. The standard for the lumber of the white oak group, all of which is marketed as white oak, is the White Oak Quercus alba. White Oak is often used to make wine barrels. The wood of the deciduous Pedunculate Oak Quercus robur and Sessile Oak Quercus petraea account for most of the European oak production, but evergreen species, such as Holm oak Quercus ilex, and Cork oak Quercus suber also produce valuable timber.
The bark of the White Oak is dried and used in medical preparations. Oak bark is also rich in tannin, and is used by tanners for tanning leather.
In Korea, oak bark (Goolpy) is used for traditional roof construction.
Acorns are used for making flour or roasted for acorn coffee.
Oak galls were used for centuries as the main ingredient in manuscript ink, harvested at a specific time of year.
Biodiversity
A number of kinds of
truffles, including the two well known varieties, the black Périgord truffle and the white Piedmont truffle, have symbiotic relationships with oak.
Diseases and pests
on pedunculate oak]]
Sudden Oak Death (
Phytophthora ramorum) is a
water mould that can kill oaks within just a few weeks.
Oak Wilt, caused by the fungus
Ceratocystis fagacearum (a fungus closely related to
Dutch Elm Disease), is also a lethal disease of some oaks, particularly the red oaks (the white oaks can be infected but generally live longer). Other dangers include
wood-boring beetles, as well as root
rot in older trees which may not be apparent on the outside, often only being discovered when the trees come down in a strong
gale.
Oak apples are
galls on oaks made by the
gall wasp. The female
kermes scale causes galls to grow on
kermes oak. Oaks are used as food plants by the
larvae of
Lepidoptera (
butterfly and
moth) species such as the
Gypsy Moth,
Lymantria dispar, which can defoliate oak and other broadleaved tree species in North America.
A considerable number of galls are found on oak leaves, buds, flowers, roots, etc. Examples are Oak artichoke gall, Oak Marble gall, Oak apple gall, Knopper gall, and Spangle gall.
A number of species of fungus cause powdery mildew on oak species. In Europe the species, Erysiphe alphitoides is the most common cause.
A new, as yet little understood disease of mature oaks, Acute oak decline, has been reported in parts of the UK since 2009.
Toxicity
The leaves and acorns of the oak tree are poisonous to
cattle,
horses,
sheep, and
goats in large amounts due to the toxin
tannic acid, and cause kidney damage and
gastroenteritis. Additionally, once livestock have a taste for the leaves and acorns, they may seek them out. Symptoms of poisoning include
lack of appetite, depression, constipation, diarrhea (which may contain blood),
blood in urine, and
colic. The exception to livestock and oak toxicity is the
domestic pig, which may be fed entirely on acorns in the right conditions, and has traditionally been pastured in oak woodlands (such as the Spanish
dehesa and the English system of
pannage) for hundreds of years. Acorns are also edible to humans in processed form, after leaching of the tanins. They are a staple part of the forage consumed by wildlife, including squirrels
and jays.
Cultural significance
National symbol
The oak is a common
symbol of
strength and
endurance and has been chosen as the
national tree of many countries. Already an ancient Germanic symbol (in the form of the
Donar Oak, for instance), certainly since the early nineteenth century it stands for the nation of
Germany. In 2004 the Arbor Day Foundation, held a vote for the official National Tree of the United States of America. In November 2004, Congress passed legislation designating the oak as America's Nation Tree.
Other countries have also designated the oak as their national tree including England, Estonia, France, Germany, Moldova, Latvia, Lithuania, Poland, the United States, Basque Country, Wales, Galicia, Bulgaria, and Serbia.
Oaks as regional and state symbols
The oak is the emblem of
County Londonderry in
Northern Ireland, as a vast amount of the county was covered in forests of the tree until relatively recently. The name of the county comes from the city of
Derry, which originally in
Irish was known as
Doire meaning
oak.
Iowa has designated the oak as its official state tree in 1961, and the White Oak is the state tree of Connecticut, Illinois and Maryland. The Northern Red Oak is the provincial tree of Prince Edward Island, as well as the state tree of New Jersey. The Live Oak is the State Tree of Georgia.
Military use
Oak leaves are traditionally an important part of German Army regalia. They also symbolize rank in the
United States Armed Forces. A gold oak leaf indicates an O-4 (
Major or
Lt. Commander), whereas a silver oak leaf indicates an O-5 (
Lt. Colonel or
Commander). Arrangements of oak leaves, acorns and sprigs indicate different branches of the
United States Navy Staff corps officers. Oak leaves are embroidered onto the covers (hats) worn by field grade officers and flag officers in the United States armed services.
If a service member earns multiple awards of the same medal, then instead of wearing a ribbon or medal for each award, he or she wears one metal representation of an "oak leaf cluster" attached to the appropriate ribbon for each subsequent award.
Political use
The oak tree is used as a symbol by a number of political parties. It is the symbol of the
Conservative Party in the
United Kingdom, and formerly of the
Progressive Democrats in
Ireland. In the cultural arena, the oakleaf is the symbol of the
National Trust (UK) and
The Royal Oak Foundation.
Mythological
In
Baltic mythology, the oak is the sacred tree of
Latvian Pērkons,
Lithuanian Perkūnas and
Prussian Perkūns. Pērkons is the god of Thunder and one of the most important deities in the Baltic pantheon.
In Celtic mythology, it is the tree of doors, believed to be a gateway between worlds, or a place where portals could be erected.
In Norse mythology, the oak was sacred to the thunder god, Thor. Some scholars speculate that this is because the oak, as the largest tree in northern Europe, was the one most often struck by lightning. Thor's Oak was a sacred tree of the Germanic Chatti tribe. Its destruction marked the Christianisation of the heathen tribes by Saint Boniface.
In Classical mythology, the oak was a symbol of Zeus and his sacred tree. An example is the oracle of Dodona, which in prehistory consisted solely of a holy oak.
In the Bible, the oak tree at Shechem is the site where Jacob buries the foreign gods of his people (Gen. 35:4) . In addition, Joshua erects a stone under an oak tree as the first covenant of the Lord (Josh. 24.25-7). In Isaiah 61, the prophet refers to the Israelites as "Oaks of Righteousness".
In Slavonic mythology, oak was the most important tree of the god Perun.
Historical
Several individual oak trees, such as the
Royal Oak in Britain and the
Charter Oak in the United States, are of great historical or cultural importance; for a list of important oaks, see
Individual oak trees.
"The Proscribed Royalist, 1651", a famous painting by John Everett Millais, depicted a Royalist fleeing from Cromwell's forces and hidden in an oak. Millais painted the picture in Hayes, Kent, from a local oak tree that became known as the Millais Oak.
The city of Raleigh, N.C. is known as "The City of Oaks."
The Jurupa Oak tree, a clonal colony of Quercus palmeria or Palmer’s Oak
found in Riverside County, California, is believed to be the world's oldest organism at 13,000 years.
Historical note on Linnaean species
Linnaeus described only five species of oak from eastern North America, based on general leaf form. These were
White oak,
Quercus alba;
Chestnut oak,
Q. Montana;
Red oak,
Q. rubra;
Willow oak Q. phellos; and
Water oak,
Q. nigra. Because he was dealing with confusing leaf forms, the
Q. prinus and
Q. rubra specimens actually included mixed foliage of more than one species. For that reason, some taxonomists in the past proposed different names for these two species (
Q. montana and
Q. borealis, respectively), but the original Linnaean names have now been lectotypified by removing some of the specimens in Linnaeus' herbarium.
Gallery
See also
List of plants poisonous to equines
Thousand Oaks, California
Foloi oak forest
Notes
Bibliography
Byfield, Liz (1990) An oak tree, Collins book bus, London : Collins Educational, ISBN 0-00-313526-8
Philips, Roger. Trees of North America and Europe, Random House, Inc., New York ISBN 0-394-50259-0, 1979.
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
Tansley, Arthur G., Sir (1952) Oaks and oak woods, Field study books, London : Methuen.
External links
Flora of China – Cyclobalanopsis
Flora Europaea: Quercus
Oaks from Bialowieza Forest
Common Oaks of Florida
Oaks of the world
Category:Articles with inconsistent citation formats
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![The Blue Oak (Quercus douglasii) is an oak in the white oak section of the genus, Quercus sect. Quercus. It is endemic to California[1] and is found in foothills surrounding the Central Valley of California[2] and certain locations in the California Coast Ranges, USA. It is also sometimes known as the Mountain Oak, and occasionally the Iron Oak.](http://web.archive.org./web/20110514053841im_/http://cdn.wn.com/pd/c5/c8/2c0e7d155e0e8ce2deb166312966_grande.jpg "The Blue Oak (Quercus douglasii) is an oak in the white oak section of the genus, Quercus sect. Quercus. It is endemic to California[1] and is found in foothills surrounding the Central Valley of California[2] and certain locations in the California Coast Ranges, USA. It is also sometimes known as the Mountain Oak, and occasionally the Iron Oak.")
![River Oaks Station Post Office, east of River Oaks in Near town. River Oaks is within Harris County Precinct 4.[69] As of 2008 Jerry Eversole is the precinct's County Commissioner.](http://web.archive.org./web/20110514053841im_/http://cdn.wn.com/pd/14/9e/5ab7562cd6a7f96743a94bf575fc_grande.jpg "River Oaks Station Post Office, east of River Oaks in Near town. River Oaks is within Harris County Precinct 4.[69] As of 2008 Jerry Eversole is the precinct's County Commissioner.")
![The Blue Oak (Quercus douglasii) is an oak in the white oak section of the genus, Quercus sect. Quercus. It is endemic to California[1] and is found in foothills surrounding the Central Valley of California[2] and certain locations in the California Coast Ranges, USA. It is also sometimes known as the Mountain Oak, and occasionally the Iron Oak.](http://web.archive.org./web/20110514053841im_/http://cdn.wn.com/pd/c5/c8/2c0e7d155e0e8ce2deb166312966_thumb.jpg "The Blue Oak (Quercus douglasii) is an oak in the white oak section of the genus, Quercus sect. Quercus. It is endemic to California[1] and is found in foothills surrounding the Central Valley of California[2] and certain locations in the California Coast Ranges, USA. It is also sometimes known as the Mountain Oak, and occasionally the Iron Oak.")
![River Oaks Station Post Office, east of River Oaks in Near town. River Oaks is within Harris County Precinct 4.[69] As of 2008 Jerry Eversole is the precinct's County Commissioner.](http://web.archive.org./web/20110514053841im_/http://cdn.wn.com/pd/14/9e/5ab7562cd6a7f96743a94bf575fc_thumb.jpg "River Oaks Station Post Office, east of River Oaks in Near town. River Oaks is within Harris County Precinct 4.[69] As of 2008 Jerry Eversole is the precinct's County Commissioner.")
