Quercus robur, commonly known as common oak, pedunculate oak, European oak or English oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is native to most of Europe west of the Caucasus. The tree is widely cultivated in temperate regions and has escaped into the wild in scattered parts of China and North America.
Quercus robur is a large deciduous tree, with circumference of grand oaks from 4 m (13 ft) to exceptional 12 m (39 ft). The Majesty Oak with a circumference of 12.2 m (40 ft 0 in) is the thickest tree in Great Britain, and the Kaive Oak in Latvia with a circumference of 10.2 m (33 ft) is the thickest tree in Northern Europe.
Quercus robur has lobed and nearly sessile (very short-stalked) leaves 7–14 cm (3–5 1⁄2 in) long. Flowering takes place in mid spring, and the fruit, called acorns, ripen by mid autumn. The acorns are 2–2.5 cm (3⁄4–1 in) long, pedunculate (having a peduncle or acorn-stalk, 3–7 cm (1–3 in) long) with one to four acorns on each peduncle.
Quercus robur is very tolerant to soil conditions and the continental climate but it prefers fertile and well-watered soils. Mature trees tolerate flooding.
It is a long-lived tree, with a large wide spreading crown of rugged branches. While it may naturally live to an age of a few centuries, many of the oldest trees are pollarded or coppiced, both pruning techniques that extend the tree’s potential lifespan, if not its health. Two individuals of notable longevity are the Stelmužė Oakin Lithuania and the Granit Oak in Bulgaria, which are believed to be more than 1500 years old, possibly making them the oldest oaks in Europe; another specimen, called the ‘Kongeegen’ (‘Kings Oak’), estimated to be about 1200 years old, grows in Jaegerspris, Denmark.