Quercus robur

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 (Latin quercus, "oak" + robur "strength, hard timber") is the type species of the genus (the species by which the oak genus Quercus is defined), and a member of the white oak section (Quercus section Quercus). The populations in Italy, southeast Europe, and Asia Minor and the Caucasus are sometimes treated as separate species, Q. brutia Tenore, Q. pedunculiflora K. Koch and Q. haas Kotschy respectively.

A close relative is the sessile oak (Q. petraea), which shares much of its range. Q. robur is distinguished from this species by its leaves having only a very short stalk (petiole) 3-8 mm (1/8-5/16 in) long, and by its pedunculate (stalked) acorns. The two often hybridise in the wild, the hybrid being known as Quercus x rosacea.

Quercus robur should not be confused with Q. rubra, the red oak, which is a native of North America and only distantly related.

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.