"oak tree") of the beech
. There are approximately 500 extant species of oaks
The common name "oak" also appears in the names of species in related genera, notably Lithocarpus
(stone oaks), as well as in those of unrelated species such as Grevillea robusta
(silky oaks) and the Casuarinaceae
(she-oaks). The genus Quercus
is native to the Northern Hemisphere, and includes deciduous
species extending from cool temperate
latitudes in the Americas
, Asia, Europe, and North Africa. North America contains the largest number of oak species, with approximately 90 occurring in the United States, while Mexico has 160 species of which 109 are endemic. The second greatest center of oak diversity is China, which contains approximately 100 species.
Solitary oak, the Netherlands
Oak: male flowers
The leaves of a young oak
Oaks have spirally
arranged leaves, with lobate margins
in many species; some have serrated leaves
or entire leaves with smooth margins. Many deciduous species are marcescent
, not dropping dead leaves until spring. In spring, a single oak tree produces both male flowers (in the form of catkins
) and small female flowers,
meaning that the trees are monoecious
. The fruit is a nut
called an acorn
or oak nut borne in a cup-like structure known as a cupule
; each acorn contains one seed (rarely two or three) and takes 6–18 months to mature, depending on their species. The acorns and leaves contain tannic acid
which helps to guard from fungi and insects.
The live oaks
are distinguished for being evergreen, but are not actually a distinct group and instead are dispersed across the genus.
The most recent classification of Quercus
divides the genus into two subgenera
and eight sections
These divisions support the evolutionary diversification of oaks among two distinct clades: the "Old World
" clade, including oaks that diversified mainly in Eurasia; and the "New World
" clade, for oaks that diversified mainly in the Americas.
- Sect. Quercus (synonyms Lepidobalanus and Leucobalanus), the white oaks of Europe, Asia and North America. Styles are short; the acorns mature in 6 months and taste sweet or slightly bitter; the inside of an acorn shell is hairless. The leaves mostly lack a bristle on their lobe tips, which are usually rounded. The type species is Quercus robur.
- Sect. Protobalanus, the 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.
- Sect. Ponticae, a disjunct including just two species. Styles are short and the acorns mature in 12 months. The leaves have large stipules, high secondary venation, and are highly toothed.
- 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.
- Sect. Lobatae (synonym Erythrobalanus), the red oaks of North America, Central America and northern South America. Styles 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.
- Sect. Cyclobalanopsis, the ring-cupped oaks of eastern and southeastern Asia. These are evergreen trees growing 10–40 m (33–131 ft) 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 forests 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).
- Sect. Cerris, the 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.
- Sect. 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.
The advent of molecular techniques for phylogenetic analysis transformed understanding of oak relationships, initially by uncovering molecular support for the diphyletic division of Quercus
into Old World and New World clades.
These techniques have proved highly useful in resolving fine-scale relationships among 2–5 oak species, particularly groups known to hybridize, but until recently the larger emphasis on this narrow approach prevented systematists from making large-scale determinations about oak history.
As the capacity for sampling across wider swaths of oak species rose, so has resolution at the section and species level across the oak tree.
Further advances in oak systematics are expected to arise from next-generation sequencing
techniques, including a recent project to sequence the entire genome of Quercus robur
(the pedunculate oak).
The recent completion of that genome has uncovered an array of mutations that may underlie the evolution of longevity and disease resistance in oaks.
In addition, the generation of RAD-seq
loci for hundreds of oak species has allowed for the construction of the most highly detailed oak phylogeny to date, although the high signal of introgression across the tree poses difficulties for deriving an unambiguous, unitary history of oaks.
Historical note on Linnaean species
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. montana
and Q. rubra
specimens actually included mixed foliage of more than one species.
Records of Quercus
have been reported from Late Cretaceous
deposits in North America and East Asia, however these are not considered definitive. In a survey of the fossil record of Quercus
it was concluded that "pre-Paleogene, and perhaps pre-Eocene occurrences of Quercus
macroremains are generally represented by poorly preserved fossils that lack critical features needed for certain identification and need to be treated with caution." The oldest unequivocal records of Quercus
date to the Eocene, around 45 million years ago.
is quite common among oaks, but usually between species within the same section only,
and most common in the white oak group. 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 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.
Frequent hybridization 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 hybridization and high levels of introgression have caused different species in the same populations to share up to 50% of their genetic information.
Having high rates of hybridization and introgression produces genetic data that often does not differentiate between two clearly morphologically distinct species, but instead differentiates populations.
Research suggests that the maintenance of particular loci for adaptation to ecological niches might explain the retention of species identity despite significant gene flow.
, or beech family, to which the oaks belong, is a very slow evolving clade
compared to other angiosperms
and the patterns of hybridization and introgression in Quercus
pose a great challenge to the concept of a species
since 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.
has a density of about 0.75 g/cm3
(0.43 oz/cu in) creating great strength and hardness. The wood is very resistant to insect and fungal attack because of its high tannin
content. It also has very appealing grain markings, particularly when quartersawn
Oak planking was common on high status Vikinglongships
in the 9th and 10th centuries. The wood was hewn from green logs, by axe and wedge, to produce radial planks, similar to quarter-sawn timber. Wide, quarter-sawn boards of oak have been prized since the Middle Ages
for use in interior panelling of prestigious buildings such as the debating chamber of the House of Commons
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 veneer production.
for aging wines
, and spirits such as brandy
, Irish whiskey
, Scotch whisky
and Bourbon whiskey
, are made from European and American oak, with single barrel whiskey
fetching a premium. The use of oak in wine
can add gustatory dimensions depending on the type of oak. Oak barrels, which may be charred before use, contribute to the colour, taste, and aroma of their potable contents, imparting a desirable oaky vanillin
flavour. A dilemma for wine producers is to choose between French and American oakwoods. French oaks (Quercus robur
, Q. petraea
) give greater refinement, and are chosen for the best, most expensive wines; while American oak contributes greater texture and resistance to ageing, but produces a more powerful bouquet.
Oak wood chips are also used for smoking
fish, meat, cheeses
and other foods.
Japanese oak is used for professional drums made by Yamaha Drums
. The higher density of oak gives the drum a brighter and louder tone compared to traditional materials such as maple
In hill states of India, besides fuelwood and timber, the locals use oak wood for agricultural implements. The leaves are used as fodder for livestock during lean periods.
A cross section of the trunk of a cork oak
, Quercus suber
Of the North American red oaks, the northern red oak
is one of the most prized for lumber, and is marketed as red oak regardless of species. This wood has open capillaries, and air blown through an end grain piece 10 inches long can send bubbles out the other end into a glass of water. The openings give fungus easy access when the finish deteriorates, and natural red oak rots easily outdoors. However, if the wood is treated with a preservative compound, the capillaries absorb it deeply, and treated red oak will resist rot better than cured white oak heartwood, which has a closed cell structure. Shumard oak
, a member of the red oak subgenus, provides timber described as "mechanically superior" to northern red oak. Cherrybark oak
is another type of red oak that provides excellent timber.
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
are used for making flour or roasted for acorn coffee.
Oak on sandy earth
Biodiversity and ecology
Harvesting and planting acorns: a short video from Wales
Oaks are keystone species
in a wide range of habitats from Mediterranean semi-desert to subtropical rainforest. For example, oak trees are important components of hardwood forests, and certain species are particularly known to grow in associations with members of the Ericaceae
in oak–heath forests
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 trees. Similarly many other mushrooms such as Ramaria flavosaponaria
also associate with oaks.
The European pied flycatcher
is an example of an animal species that often depends upon oak trees.
Many species of oaks are under threat of extinction in the wild, largely due to land use changes, livestock grazing and unsustainable harvesting. For example, over the past 200 years, large areas of oak forest in the highlands of Mexico, Central America and the northern Andes have been cleared for coffee plantations and cattle ranching. There is a continuing threat to these forests from exploitation for timber, fuelwood and charcoal.
In the US, entire oak ecosystems have declined due to a combination of factors still imperfectly known, but thought to include fire suppression, increased consumption of acorns by growing mammal populations, herbivory of seedlings, and introduced pests.
However, it has also been suggested that oaks as generally light-demanding trees with a relatively high tolerance for mechanic disturbances might depend on grazers like bison
and the clearances they create in order to regenerate successfully, thus missing them since they were extirpated in most regions following the European colonization
The mature trees shed varying numbers of acorns annually. Scientists suggest that shedding excess numbers allows the oaks to satiate nut gathering species which improves the chances of germination. Every four to ten years, certain oak populations will synchronize to produce almost no acorns at all, only to rain them down excessively the following year, known as a "mast" year. The year preceding the mast year is thought to starve off the mammal populations feeding on the supply, thereby increasing the effectiveness of the overproduction in the mast year that follows.
This is necessary to the survival of any given oak species, as only one in 10,000 acorns results in an eventual tree.
Diseases and pests
Sudden oak death
) is a water mould
that can kill oaks within just a few weeks. Oak wilt
, caused by the fungus Bretziella fagacearum
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 being discovered only when the trees come down in a strong gale
. Oak apples
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
) species such as the gypsy moth
, Lymantria dispar
, which can defoliate oak and other broadleaved tree species in North America.
A new and yet little understood disease of mature oaks, acute oak decline
, has been reported in parts of the UK
The oak processionary
moth (Thaumetopoea processionea
) has become a serious threat 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.
The eastern grey squirrel
) is an invasive species across North America and Europe where they are known to strip bark off of a variety of large trees, including oaks. Bark stripping can result in the death of the leading shoot
and decreased crown
According to a comprehensive report by The Morton Arboretum
and the International Union for Conservation of Nature (IUCN) an estimated 31% of the world's estimated 430 oak species are threatened with extinction, while the study found an estimated 41% of oak species to be of conservation concern.
The countries with the highest numbers of threatened oak species according to the report are China
with 36 species, Mexico
with 32 species, Vietnam
with 20 species and the USA
with 16 species. While the cause of decline is still partly unknown for some species, the main causes the scientists determined were climate change
and invasive pests in the US, and deforestation
In the Himalayan region of India, oak forests are being invaded by pine forests due to the increase in temperature. The associated species of pine forest may cross frontiers and become new elements of the oak forests.
The leaves and acorns of the oak tree are poisonous in large amounts to livestock including cattle
, and goats
due to the toxin tannic acid
, causing kidney damage and gastroenteritis
. Symptoms of poisoning include lack of appetite
, depression, constipation, diarrhea (which may contain blood), blood in urine
, and colic
. The exception 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
The oak is a common symbol
and has been chosen as the national tree
of many countries. In England, oaks have been a national symbol since at least the sixteenth century, often used by Shakespeare to convey heritage and power. In England today they remain a symbol of the nation's history, traditions, and the beauty of its countryside. 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
and oak branches are thus displayed on some German coins, both of the former Deutsche Mark
and the current euro
In 2004 the Arbor Day Foundation
held a vote for the official National Tree of the United States of America
. In November 2004, the United States Congress
passed legislation designating the oak as America's National Tree.
Other countries have also designated the oak as their national tree including Bulgaria
, and Wales
Oaks as regional and state symbols
The oak in the former coat of arms of Ekenäs
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
The Irish County Kildare
derives its name from the town of Kildare
which originally in Irish
was Cill Dara
meaning the Church of the Oak or Oak Church.
The coat-of-arms of the municipality Eigersund
, Norway features an oak leaf.
Oak leaves are traditionally an important part of German Army regalia.
The Nazi party used the traditional German eagle, standing atop of a swastika inside a wreath of oak leaves. It is also known as the Iron Eagle. During the Third Reich of Nazi Germany, oak leaves were used for military valor decoration on the Knights Cross of the Iron Cross. They also symbolize rank in the United States Armed Forces
. A gold oak leaf indicates an O-4 (major
or lieutenant commander
), whereas a silver oak leaf indicates an O-5 (lieutenant colonel
). Arrangements of oak leaves, acorns and sprigs indicate different branches of the United States Navy staff corps
Oak leaves are embroidered onto the covers (hats) worn by field grade officers and flag officers in the United States armed services.
If a member of the United States Army or Air Force 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.
Grīdnieku ancient oak in Rumbas parish, Latvia
, girth 8.27 m, 2015
The prehistoric Indo-European
tribes worshiped the oak and connected it with a thunder or lightning 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
, the sacred oak was the centerpiece of the precinct, and the priests would divine the pronouncements of the god by interpreting the rustling of the oak's leaves.
In Celtic polytheism
, the name of the oak tree was part of the Proto-Celtic word for 'druid': *derwo-weyd-
; however, Proto-Celtic *derwo-
) can also be adjectives for 'strong' and 'firm', so Ranko Matasovic interprets that *druwid-
may mean 'strong knowledge'. As in other Indo
-European faiths, Taranis
, being a thunder god, was associated with the oak tree.
"Tree" and drus
may also be cognate with "Druid," the Celtic priest to whom the oak was sacred. There has even been a study that shows that oaks are more likely to be struck by lightning than any other tree of the same height.
The oak also appears in the Hebrew tradition. In the Bible
, the oak tree at Shechem
is the site where Jacob buries the foreign gods of his people (Gen. 35:4). Also, 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". Absalom's long hair (2 Samuel 18:9) gets caught in an oak tree, and allows Joab to kill him.
Vereration of the oak survives in Serbian Orthodox Church
celebrations include the badnjak
, a branch taken from a young and straight oak ceremonially felled early on Christmas Eve morning, similar to a yule log
. In recent times, only the branches are collected, brought home, and ceremoniously thrown into a stove or church bonfire. In another tradition, a zapis
(lit. "inscription") is an old, isolated oak on a hilltop or promontory, often inscribed with a cross by a parish priest. Reverence for zapisi
probably originated in pre-Christian times, and they long remained places of public gathering and even of Christian worship where churches were not available. For example, in 1815, at a zapis
assembly in Takovo, knezMiloš Obrenović
declared the start of the Second Serbian Uprising
. Even in modern times, cutting down zapis
oaks can result in public outcry, even for projects like road building.
In some traditions of Wicca
, the Oak King is one of the two faces of the Sun God. He is born on Yule and rules from Ostara to Mabon.
Several oak trees, such as the Royal Oak
in Britain and the Charter Oak
in the United States, are of great historical or cultural importance.
The Jurupa Oak
tree – a clonal colony of Quercus palmeri
or Palmer's oak found in Riverside County, California – is an estimated 13,000 years old.
Large groups of very old oak trees are rare[why?]
. One venerable group found in Poland, is about 480 years old, as assessed by dendrochronology.
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 oak crown
Famous oak trees
in Henryków Poland
, the name refers to the steel fittings that fasten the damage to the tree.
- The Emancipation Oak is designated one of the 10 Great Trees of the World by the National Geographic Society and is part of the National Historic Landmark district of Hampton University in Virginia.
- The Ivenack Oak which is one of the largest trees in Europe is located in Mecklenburg-Vorpommern, Germany, and is approximately 800 years old.
- The Bowthorpe Oak, located in Bourne, Lincolnshire, is thought to be 1,000 years old. It was featured in the Guinness Book of World Records and was filmed for a TV documentary for its astonishing longevity.
- The Minchenden (or Chandos) Oak, in Southgate, London, is said to be the largest oak tree in England (already 8.2 m or 27 ft in girth in the nineteenth century), and is perhaps 800 years old.
- The Seven Sisters Oak is the largest certified southern live oak tree. Located in Mandeville, Louisiana, it is estimated to be up to 1,500 years old with a trunk that measures 11.6 m (38 ft).
- The Major Oak is an 800- to 1000-year-old tree located in Sherwood Forest, Nottinghamshire. According to folklore, it was used by Robin Hood for shelter.
- Friendship Oak is a 500-year-old southern live oak located in Long Beach, Mississippi.
- The Crouch Oak is believed to have originated in the 11th Century and is located in Addlestone, Surrey. It is an important symbol of the town with many local businesses adopting its name. It used to mark the boundary of Windsor Great Park. Legend says that Queen Elizabeth I stopped by it and had a picnic.
- The Angel Oak is a southern live oak located in Angel Oak Park on John's Island near Charleston, South Carolina. The Angel Oak is estimated to be in excess of 400–500 years old, stands 20.3 m (661⁄2 ft) tall, and measures 8.5 m (28 ft) in circumference.
- The Kaiser's Oak, located at the village of Gommecourt in Artois, France, named in honour of Kaiser Wilhelm II, symbolically marked from late 1914 to April 1917 the furthest point in the West of the German Imperial Army during World War I.
- The Wye Oak in Maryland was the United States' largest white oak tree before it blew down in a storm in 2002, at an estimated age of 460 years.
- The Bland Oak in Sydney, Australia, planted in the 1840s, was the largest tree in Australia until it was split in a storm early on New Year Day 1941.
- The Treaty Oak in Austin, Texas, is a Texas live oak, and the last surviving member of the Council Oaks, a grove of 14 trees that served as a sacred meeting place for Comanche and Tonkawa tribes prior to European settlement of the area.
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