Oak

An oak is a type of hardwood tree or shrub that belongs to the genus Quercus in the beech family. These trees have leaves with edges that look like they have sections, and they produce a nut called an acorn.

Oaks are very important in nature. They give homes and food to many animals, including insects and fungi. Oak wood is strong and is used to build things and make furniture. Oak bark was once used for tanning leather. Today, oak wood is used to make barrels for drinks like sherry and whisky.

The oak tree is a symbol of strength and is the national tree of some countries. It appears in many old stories and religions. Some famous oak trees include the Royal Oak in Britain, the Charter Oak in the United States, and the Guernica Oak in the Basque Country. Many oak species are at risk because of changes in the climate and harmful invasive pests.

Etymology

The name Quercus comes from an old Latin word for "oak". This word started from an even older language called Proto-Indo-European. The word "cork" for the special bark of the cork oak also comes from Quercus. The common word "oak" comes from Old English, which itself came from an older language called Proto-Germanic.

Description

Oaks are hardwood trees that may lose their leaves or keep them all year. Their leaves are arranged in a spiral pattern and often have edges that look like lobes. In spring, an oak tree grows both male and female flowers. The male flowers form clusters called catkins, while the female flowers produce an acorn, a special kind of nut.

There are about 500 different kinds of oaks in the world.

Some oak trees grow very large and live for many years. Even smaller oaks, like the Japanese evergreen oak, can grow tall.

Evolution

Fossil history

Scientists think oaks may have existed as far back as the Late Cretaceous in North America and East Asia. But this is not certain. The oldest clear proof of oaks is from pollen in Austria, from about 55 million years ago. In North America, the oldest oak fossils are from Oregon, about 44 million years old. In Asia, they are from Japan, from the Middle Eocene time.

External phylogeny

Oaks are part of the Quercoideae subfamily in the beech family, Fagaceae. New science with genes has helped us learn how oaks are related.

Internal phylogeny

Genes show oaks split into two groups: those from the Old World (Europe, Asia, and Africa) and those from the New World (the Americas). Because oaks often share genes, it is hard to make a clear family tree.

Taxonomy

The group Quercus was first named by Carl Linnaeus in 1753. A new way to group them splits oaks into two subgenera and eight sections.

Taxonomic history

Linnaeus named 15 oak kinds when he first described the group Quercus. He chose Quercus robur, the pedunculate oak, as the main example.

Subgenus Quercus

This group has oaks mostly from North America. It has several sections:

• Section Lobatae: The red oaks from North and South America. Their acorns take 18 months to grow and are very bitter.
• Section Protobalanus: The canyon live oaks and their close friends in the southwest United States and northwest Mexico. Their acorns also take 18 months and are very bitter.
• Section Ponticae: A small group with only two kinds. Their acorns grow in 12 months.
• Section Virentes: The southern live oaks of the Americas. Their acorns grow in 12 months, and their leaves stay green all year.
• Section Quercus: The white oaks of Europe, Asia, and North America. Their acorns grow in one or two years, and their leaves often have rounded ends without points.

Subgenus Cerris

This group has oaks from Eurasia and Africa. It also has several sections:

• Section Cyclobalanopsis: The ring-cupped oaks of east and southeast Asia. These are trees that stay green and can grow very tall.
• Section Cerris: The Turkey oak and its relatives in Europe and Asia. Their acorns take 18 months to grow and are very bitter.
• Section Ilex: The Ilex oak and its relatives in Eurasia and north Africa. Their acorns take between 12 and 24 months to grow, and their leaves stay green all year with tiny points on the edges.

Distribution

Oaks grow in the Northern Hemisphere. You can find them in the Americas, Asia, Europe, and North Africa. North America has the most oak species. China is the second place with the most oak species.

In the Americas, oaks grow from Vancouver and Nova Scotia in Canada, down to Mexico and across the eastern United States. They are also found in a small part of western Cuba and in Mesoamerica. In the Old World, oaks grow all over Europe, except the far north, and in north Africa from Morocco to Libya. They are also in Turkey, the Middle East, Iran, Afghanistan, and Pakistan. Some oaks grow in the western Caucasus in Turkey and Georgia. Others are found along the Himalayas, stretching to Sumatra, Java, Borneo, and Palawan. Finally, oaks grow in east Asia, including China, Korea, and Japan.

Ecology

Oaks are important trees that grow in many places, from dry lands to rainforests. They are part of forests and sometimes grow with special plants called Ericaceae. Some types of truffles, like the black Périgord truffle and the white Piedmont truffle, live close to oak trees and help them grow.

Oaks provide food for many animals, especially caterpillars that birds eat. Oak trees produce acorns, which are like nuts, and these acorns fall to the ground each year. Animals like squirrels and jays pick up these acorns and hide them, which helps spread new oak trees.

Hybridisation

Oaks can sometimes mix with other oak types to create new kinds of oaks. This happens often in groups called white oaks. These oaks cannot tell if they are being pollinated by another oak type, so they allow it. This mixing creates new oak types that can live in different places.

Diseases and pests

Oaks can get sick or be eaten by many tiny creatures. In Britain, some oak types have over 400 different insects that live on them. These insects change through the seasons, with some eating the leaves and others sucking the sap. Some diseases, like powdery mildews, can make the leaves fall off early.

In the UK, a moth called the oak processionary has become a problem. Its caterpillars can strip leaves from trees and their tiny hairs can make people uncomfortable. In California, a beetle called the goldspotted oak borer has hurt many oak trees. Another disease called sudden oak death has also damaged oaks in California and Oregon, and it has been found in Europe.

Gall communities

Many small growths called galls can appear on oak leaves, buds, flowers, and roots. These galls are made by tiny wasps. Inside these galls, other tiny wasps lay their eggs. Some other tiny creatures also live inside the galls.

• Oak apple gall on Quercus garryana

• Oak apples on oak leaf

• Biorhiza pallida male, the cause of oak apple galls

Conservation

Many oak trees around the world are in danger of disappearing. Some oak trees need special care to stay safe.

The main reasons oaks are threatened are changes in weather, harmful insects in the US, and cutting down forests in Asia. In some places, like India, oak forests are being taken over by pine trees because of warmer temperatures. In Mexico and Central America, oak forests have been cleared to make space for coffee farms and cattle. Oaks also face threats from people cutting them for wood, fuel, and charcoal.

Toxicity

The leaves and acorns of oak trees can be harmful to animals like cattle and horses if they eat too much, because of a substance called tannic acid. This can hurt their kidneys and stomachs. Pigs can safely eat acorns under certain conditions. People have used acorns as food for a long time after washing them in water.

Uses

Oak wood is strong and hard, so it is great for furniture, floors, and building frames. It does not break easily and stays safe from bugs and fungi. Long ago, people in Europe used oak to build ships.

Oak has many other uses. The bark, which has a substance called tannin, was used to treat leather. Special growths on oak called galls were used to make ink for old writings. In some places, oak bark was used for roofs and medicines. Acorns from oak trees can be ground into flour or roasted to make a drink like coffee.

Oak barrels are used to age wines, sherry, and spirits like brandy and Scotch whisky. They add flavor and color to these drinks. Oak wood chips are also used to add flavor when smoking food like fish, meat, and cheese. In Japan, oak leaves are used to wrap special rice cakes for a holiday. The bark of a special kind of oak called cork oak is used to make bottle stoppers for wine.

Culture

The oak tree is a symbol of strength and lasting power. Many countries, such as the US, Bulgaria, Croatia, Cyprus, Estonia, France, Germany, and Wales, consider it their national tree. In Ireland, the city of Derry is named after the oak tree. Oak leaves and branches appear on coins and in military symbols.

In ancient times, people respected the oak tree. In Greek stories, it was sacred to Zeus, the king of the gods. In Norse and Baltic traditions, it was linked to the thunder gods Thor and Perkūnas. The word "druid," used for Celtic priests, comes from an ancient word for "oak." Today, some Christian traditions still honor the oak during Christmas celebrations.