Quercus robur, pedunculate oak, European oak, or English oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native to Europe and western Asia, and is widely cultivated in other temperate regions. It grows on soils of near neutral acidity in the lowlands and is notable for its value to natural ecosystems, supporting a diversity of herbivorous insects, acorn eating mammals and birds, and fungi. The common name pedunculate oak refers to the acorns being borne on a peduncule, or stalk. English oaks can live to very old ages, often growing for over 500 years, with some specimens believed to be over 1,000 years old They are characterised by thick and heavily fissured bark.
Description Pedunculate oak is a deciduous tree, typically maturing at up to 20 m in height, and sometimes up to 40 metres (130 ft), with a single stout trunk typically reaching up to 4 m, sometimes exceeding 10 m (33 ft) in girth (circumference at breast height), or even reportedly 14 m in pollarded specimens. Older trees tend to be pollarded, with boles (the main trunk) about 3 m long. They often live longer and become more stout than unpollarded trees.
The crown is spreading and unevenly domed, and trees often have massive lower branches. The bark is greyish-brown and closely grooved, with vertical plates. There are often large burrs on the trunk, which typically produce many small shoots. Oaks do not produce suckers but do recover well from pruning or lightning damage. The twigs are hairless and the buds are rounded (ovoid), brownish and pointed. The leaves are arranged alternately along the twigs and are broadly oblong or ovate, 10–12 cm long by 7–8 cm wide, with a short (typically 2–3 mm) petiole. They have a cordate (auricled) base and 3–6 rounded lobes, divided no further than halfway to the midrib. The leaves are usually glabrous or have just a few simple hairs on the lower surface. They are dark green above, paler below, and are often covered in small disks of spangle gall by autumn.
Flowering takes place in spring (early May in Northern Europe) and the flowers are wind-pollinated. The male flowers occur in narrow catkins some 2-4 cm long and arranged in small bunches. The female flowers are small, brown with dark red stigmas, about 2 mm in diameter and are found at the tips of new shoots on peduncles 2–5 cm long. The fruits (acorns) are borne in clusters of 2–3 on a long peduncle (stalk) 4–8 cm long. Each acorn is 1.5–4 cm long, ovoid with a pointed tip, starting whitish-green and becoming brown, then black. The acorns are carried in a distinctive shallow cup which can be useful in identifying the species. It is an "alternate bearing" species, with large crops produced every other year.
Chemistry Grandinin/roburin E, castalagin/vescalagin, gallic acid, monogalloyl glucose (glucogallin) and valoneic acid dilactone, monogalloyl glucose, digalloyl glucose, trigalloyl glucose, rhamnose, quercitrin and ellagic acid are phenolic compounds found in Q. robur. The heartwood contains triterpene saponins.
Similar species Q. robur is most likely to be confused with sessile oak, which shares much of its range. Distinguishing features of Q. robur include the auricles at the leaf base, the very short petiole, its clusters of acorns being borne on a long peduncle, and the lack of stellate hairs on the underside of the leaf. The two often hybridise in the wild, forming Quercus × rosacea. Turkey oak is also sometimes confused with it, but that species has "whiskers" on the winter buds and deeper lobes on the leaves (often more than halfway to the midrib). The acorn cups are also very different.
Taxonomy Quercus robur (from the Latin quercus, "oak" + robur derived from a word meaning robust, strong) was named by Carl Linnaeus in Species Plantarum (1753). It is the type species of the genus and classified in the white oak section (Quercus section Quercus). The genome of Q. robur has been completely sequenced (GenOak project); the first version was published in 2016. It comprises 12 chromosome pairs (2n = 24), about 26,000 genes and 750 million bp. There are many synonyms, and numerous varieties and subspecies have been named. The populations in Iberia, Italy, southeast Europe, and Asia Minor and the Caucasus are sometimes treated as separate species, Q. orocantabrica, Q. brutia Tenore, Q. pedunculiflora K. Koch and Q. haas Kotschy respectively. Quercus × rosacea (Q. petraea x Q. robur) is the only naturally occurring hybrid, but the following crosses with other white oak species have been produced in cultivation:
Q. × bimundorum (Q. alba × Q. robur) (two worlds oak) Q. × macdanielli (Q. macrocarpa × Q. robur) (heritage oak) Q. × turneri Willd. (Q. ilex × Q. robur) (Turner's oak) Q. × warei (Q. robur 'Fastigiata' x Q. bicolor). There are numerous cultivars available, among which the following are commonly grown:
'Fastigiata', cypress oak, is a large imposing tree with a narrow columnar habit. 'Concordia', golden oak, is a small, very slow-growing tree, eventually reaching 10 m (33 ft), with bright golden-yellow leaves throughout spring and summer. It was originally raised in Van Geert's nursery at Ghent in 1843. 'Pendula', weeping oak, is a small to medium-sized tree with pendulous branches, reaching up to 15 m (49 ft). 'Purpurea' is another small form, growing to 10 m (33 ft), with purple leaves. 'Pectinata' (syn. 'Filicifolia'), cut-leaved oak, is a cultivar where the leaf is pinnately divided into fine, forward-pointing segments.
Names Quercus robur has numerous common names including pedunculate oak, common oak, European oak, or English oak. In French it is called chêne pédonculé. As a wood product its timber will often be called French oak, Polish oak, Slavonian oak, or similar names based upon its geographic origin.
Distribution The species is native to most of Europe and western Asia, and is widely cultivated in other temperate regions.
Habitat and ecology Pedunculate oak is a long-lived tree of high-canopy woodland, coppice and wood pasture, and it is commonly planted in hedges. It is rare on thin, well-drained calcareous (chalk and limestone) soil. Sometimes it is found on the margins of swamps, rivers and ponds, showing that it is fairly tolerant of intermittent flooding.
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