Trinity Tree of the Month - Sessile Oak

Posted on: 23 May 2023

This month we are bringing you another of our Native Tree Species, Quercus petrea or Sessile Oak, which was declared Ireland’s National Tree. Tree no. 258, the Quatercentenary Oak is, located in New Square opposite House 39. A larger specimen, no. 528, can be found beside The Flatiron.

This species is often confused with Quercus robur (English Oak). Q. robur bears clusters of acorns on a long peduncle (stalk), while the Sessile Oak bears its acorns on short stalks and leaves on long stalks. The tree was once widespread throughout Ireland but centuries of over-harvesting and lack of replacement have resulted in truly native oak being hard to find. Tree 258 was kindly provided by the National Parks & Wildlife Service, with a known provenance of Killarney National Park. 

In Medieval Ireland, the oak was one of the seven ‘Nobles of the Wood’ and was protected under the old Brehon Law; lesser trees were in a division known as the ‘Commoners of the Wood’. Eó Mugna (Oak tree) was also regarded as one of the ‘Guardian Trees of Ireland’, each of which sheltered one of the then five provinces of Ireland.

The oak tree symbolises strength, resilience and longevity and has been held a sacred tree for thousands of years. It is firmly steeped in folklore, Irish history and European history. To the Greeks, the oak was sacred to the god Zeus and in Ireland was sacred to Dagda. 

Oak is the seventh tree in the Ogham alphabet, ‘Dair’. In Ireland, many pre-Christian and Christian sites were named for the Oak, and are well recognised place names today, such as Cill Dara (Kildare) meaning Church of the Oak which was founded by St Brigid.

Oak trees support more wildlife than any other native trees, providing habitat for up to 280 species of insect. Its bark provides a habitat for mosses, lichens, liverworts and some ferns. In mature trees deadwood cavities also provide homes for nesting birds and roosting bats, while the acorns provide a valuable food source for several wildlife.

Oaks are angiosperms, meaning they produce their seed within a fruit. They are monoecious, bearing both male and female flowers on the same tree. The Oak is a member of the Fagaceae (Beech) family. Generally, 20-30 metres in height with 4 metre girth, they can attain up to 40 metres in height and 15 metres girth and can live for up to 1000 years. Our campus tree is still very young by comparison, but when it reaches maturity, it will store up 7,500 tonnes of carbon.

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• Environment
• Sustainability