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Quick facts

Common name: sessile oak

Scientific name: Quercus petraea

Family: Fagaceae

Origin: native

Sessile oak is a deciduous broadleaf tree which can grow 20–40m tall.

Look out for: leaves which are lobed with a long leaf stalk. The leaf lobes are shallow.

Identified in winter by: rounded buds which are in clusters. Each bud has more than three scales.

What does sessile oak look like?

Sessile oak leaf close-up against blue sky

Credit: Blickwinkel / Alamy Stock Photo

Leaves

Dark green and lobed, with an undulate margin.

Sessile oak flowers

Credit: FloralImages / Alamy Stock Photo

Flowers

Sessile oak is monoecious, meaning male and female flowers are found on the same tree. Male flowers are green catkins and female flowers are inconspicuous clusters of bracts (modified leaves), which resemble red flower buds.

Close up of three young green Sessile oak acorns.

Credit: Leaves galore / Den Reader / Alamy Stock Photo

Fruits

After pollination by wind, female flowers develop into a large shiny seed held in a scaly wooden cup, commonly known as an acorn. Young acorns are green, maturing to brown before they fall.

Not to be confused with:

English, or pedunculate, oak (Quercus robur). Sessile oak has stalkless (sessile) acorns and the two species often hybridise. It has a more upright trunk and straighter branches than English oak, and the leaves have longer stalks.

Child and parent looking at autumn leaves with magnifying glass

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Where to find sessile oak

It is the official national tree of Ireland and is native to most of Europe, commonly located in hilly regions.

Did you know?

Over its lifespan, an oak tree can produce as many as five million acorns.

Value to wildlife

Whether sessile or pedunculate, oak trees support more wildlife than any other native trees. They provide a habitat for more than 257 species of insect, which are the food source for birds and other predators. The bark also provides a habitat for mosses, lichens and liverworts, and deadwood cavities for nesting birds and roosting bats. The acorns are eaten by a number of birds and mammals, including the jay, badger and red squirrel.

Flower and leaf buds of English and sessile oak are the food plants of the caterpillars of purple hairstreak butterflies.

The soft leaves break down with ease in autumn and form a rich leaf mould beneath the tree, supporting beetles and numerous fungi, such as the oakbug milkcap.

Mythology and symbolism

The oak was sacred to many gods including Zeus, Jupiter and the Celtic Dagda. Each of these gods ruled over thunder and lightning, and oak trees are often hit by lightning as they are the tallest living feature in the landscape.

Druids practised rituals in oak groves and cherished the mistletoe that grows in oak tree branches. It’s also linked with royalty: ancient kings and Roman Emperors wore crowns of oak leaves.

In England, the oak is a national symbol of strength. Couples were wed under ancient oaks in Oliver Cromwell’s time. Oak is the emblem of many environmental groups, including the Woodland Trust.

Did you know?

Every five to 10 years, depending on conditions, there’s a bumper crop in what is referred to as a mast year, when the tree produces up to 10,000 acorns in one season.

Uses of sessile oak

Oaks produce one of the hardest and most durable timbers on the planet. However, it takes up to 150 years before an oak is ready to use in construction. It has been a prized hardwood timber for thousands of years and is still used for flooring, wine barrels and firewood.

Other uses of oak:

  • Leaves, bark and acorns were believed to heal many medical ailments, including diarrhoea, inflammation and kidney stones.
  • Acorns have also been used to make bread flour.
  • Tannin found in the bark has been used to tan leather since at least Roman times.

Threats and conservation

Acute oak decline and chronic oak decline are serious conditions affecting Britain’s oaks, with several contributing factors linked to the diseases. Decline of mature oaks first caused concern in the 1920s and today, most cases are in central, southern and eastern England. 

The oak processionary moth is a non-native pest that has been found in London, Surrey and Berkshire. Not only does it damage the foliage of the trees and increase the oak’s susceptibility to other diseases, it is actually a risk to human health. The moth’s hairs are toxic and can lead to itching and respiration problems.