The oak produces the acorns that are a defining food of many oak-forest ecosystems.
Oaks belong mainly to the genus Quercus, which contains hundreds of species across the Northern Hemisphere. Their fruit is an acorn, a nut partly enclosed by a cup-like structure called a cupule. Acorns mature at different rates depending on the oak group: some species produce them in one season, while others take two years.
Acorns support wildlife such as jays, squirrels, deer and wild boar. Animals that carry and bury acorns can also help oaks regenerate, although many buried seeds are later recovered or eaten. Oak leaves, bark and wood support additional insects, fungi and other organisms.
The name “oak” covers many species, including English oak, white oak and cork oak. They are not all evergreen, and their leaves vary greatly. Oak wood has long been used for buildings, ships, flooring and barrels, while the trees have also played important roles in folklore and national symbolism.