Tree or shrub, genus Quercus noted for lobed leaves and 'acorn' seeds.

An oak is a tree or shrub of genus Quercus (Family Fagaceae). This genus contains about 600 species, but confusingly the common name 'oak' is also used in the names of species of some related genera (e.g. Lithocarpus). Oaks are native to the Northern Hemisphere, extending from high latitudes down into tropical Asia and the Americas. The genus includes both evergreen and deciduous species. Evergreen oaks are known as 'live oaks' but they are not a botanically distinct group and instead are distributed through the genus.

Oaks are flowering plants. Leaves are arranged spirally, and often have a characteristic lobed shape. Flowers are in the form of catkins, and produce a characteristic nut known as an acorn. The acorn is born in a cup structure (a 'cupule'). The acorn nut contains high levels of tannic acid, making them poisonous to most ungulates. They are edible to humans although the tannic acid makes them bitter, so they are usually processed to leach the tannins and make them more palatable. They are a staple for other animals such as squirrels and jays.

Many oak trees can grow as large, old trees (a typical English Oak can easily live to 1000 years), and it is a common symbol of strength and endurance. For example the Royal Navy song "Hearts of Oak" - inspired by the use of English oak in wooden ships. Similarly, the Donar Oak is an ancient symbol for the German nation, and oak leaves often appear on German Army regalia.

Use this tag for all questions about growing and caring for oak trees (and shrubs).