Oak belongs to the genus Quercus of the beech, or Fagaceae, family.
There are approximately 600 extant species of oaks.
Oak trees are native to the Northern hemisphere.
Oak trees are found from cool temperate to tropical latitudes in the Americas, Asia, Europe, and North Africa.
Most species of oak trees are deciduous with only a few of evergreen forms.
The usual lifespan of an oak is about 200 years, but some live over 1,000 years.
The Pechanga Great Oak Tree, oldest oak tree in the United States, possibly in the world. It is estimated to be up to 2,000 years old.
Oak trees grow to an average height of about 15 to 21 meters (50 to 70 feet) and have a spread of as much as 15 meters (50 feet) from branch to branch when fully grown.
The white oak is the tallest oak species. The tallest known white oak is 44 meters (144 feet) tall. It is not unusual for a white oak tree to be as wide as it is tall.
Oaks have spirally arranged leaves, with lobate margins in many species; some have serrated leaves or entire leaf with smooth margins.
In spring, a single oak tree produces both male flowers (in the form of catkins) and small coon flowers (female flowers). Oak trees have male flowers on one part of their branch, and female flowers on another part of the same branch.
The fruit is a nut called an acorn, borne in a cup-like structure. Production of acorns starts at the age of 20 to 50 years. Each acorn contains one seed (rarely two or three) and takes 6–24 months to mature, depending on their species.
One oak produces more than 2000 acorns every year, but only one in 10 000 acorns will manage to develop into oak tree.
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.
Oaks are keystone species in a wide range of habitats from Mediterranean semi-desert to subtropical rainforest.
Many species of oaks are under threat of extinction in the wild, because of the habitat destruction, over exploitation, diseases and introduction of invasive species.
Oak wood has great strength and hardness. The wood is very resistant to insect and fungal attack because of its high tannin content. It is used in the manufacture of ships, furniture, floorings and Yamaha drums.
Also barrels in which wines, sherry, and spirits such as brandy, Irish whiskey, Scotch whisky and Bourbon whiskey are aged are made from European and American oak. Oak barrels contribute to the color, taste, and aroma of the contents, imparting a desirable oaky vanillin flavour to these drinks. The use of oak in wine can add many different dimensions to wine based on the type and style of the oak.
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.
The oak is a common symbol of strength and endurance and has been chosen as the national tree of many countries. Oak is national tree of USA, Germany, Serbia, Cyprus, England, Estonia, France, Moldova, Romania, Jordan, Latvia, Lithuania, Poland, Wales and Bulgaria.
In Greek mythology, the oak is the tree sacred to Zeus, king of the gods.
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.” Absalom’s long hair (2 Samuel 18:9) gets caught in an oak tree, and allows Joab to kill him.
The badnjak is central tradition in Serbian Orthodox Church Christmas celebration where young and straight oak, is ceremonially felled early on the morning of Christmas Eve. The badnjak is brought into the house and placed on the fire on the evening of Christmas Eve.
In Republican Rome a crown of oak leaves was given to those who had saved a life of a citizen in battle; it was called the “civic oak”
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.
Although it is rarely reached, the symbol of an 80th wedding anniversary is oak.
Oaks are more likely to be struck by lightning than other trees. This enhances their significance for Druids who seek ‘arwen’ or inspiration which they believe can come through lightning. They call this ‘courting the flash’.
In Britain, an oak tree image is engraved in a six pence coin. It is one of the oldest Britain’s coins.
Oak branches are displayed on some German coins, both of the former Deutsche Mark and the current Euro currency.
The Royal Oak is the third most common pub name in Britain.