Oak belongs to the genus Quercus which comprises over 600 different species of trees. Most species of oak trees are deciduous with only couple of evergreen forms. Oak trees live on the Northern hemisphere. They can survive in various forests, including those in temperate climates, Mediterranean and tropical areas. Oak trees are prone to fungal diseases that may induce rotting of the inner part of the plant. Besides fungi, insects often attack oaks and induce defoliation (removal of the leaves). 78 species of oaks are listed as endangered because of the habitat destruction, over exploitation, diseases and introduction of invasive species.
Oak trees are usually large in size. They can reach 70 feet in height and 9 feet in width. Their branches can reach 135 feet in length.
One of the biggest oaks is located in Goose Island State Park. This oak is 45 feet tall, 35 feet wide, with crown that has 90 feet in diameter.
Due to its large dimensions, oak requires large amount of water per day. It can absorb 50 gallons of water each day.
Oaks have leaves that can be lobed, serrated or flat on the edges. Certain species have leaves with bristles.
Oaks produce both male and female flowers. Male flowers are arranged in clusters called catkins. Female flowers are much smaller.
Fruit of the oak is called acorn. Production of acorns starts at the age of 20 to 50 years.
Oaks produce more than 2000 acorns every year, but only one in 10 000 acorns will manage to develop into oak tree.
A lot of animals (pigeons, duck, pigs, deer, squirrels, mice…) feed on acorns.
Young acorns, leaves and buds contain tannic acid which induces toxic effects in cattle. Tannic acid may induce formation of ulcers in the stomach, damage in kidneys and result in malformation in the newly born cattle.
Wood of oak is very strong and hard. It is used in the manufacture of ships, furniture, floorings and Yamaha drums.
Oak is also used in the manufacture of barrels for storing of vine, whiskey, brandy and other liquors. Oak wood adds special aroma to these beverages.
Oak is national plant of many countries including USA, England, France, Germany, Latvia, Poland and Serbia. It symbolizes strength and endurance.
Oak is also used in army ranking. Silver leaf indicates Lt. Colonel while gold leaf indicates Lt. Commander.
One of the oldest Britain's coins (six pence) has an oak engraved on one of the surfaces.
Most species of oaks live over 200 years. There are certain trees that can survive over thousand years. Oak tree planted during the reign of King John managed to survive 800 years and reign of 35 other rulers.