Plant 163

Quercus ilex L. (Fagaceae)


Holm oak

The holm oak has been cultivated in Britain since the sixteenth century. However, to many, it remains a somewhat unfamiliar relative of the English oak (Quercus robur). Native to the Mediterranean, where it grows predominantly in maquis scrubland and mixed woodland along coastal and inland areas, it has excellent resistance to drought and wildfire. Holm oak once covered large areas of the Mediterranean Basin; today its stronghold is the Iberian Peninsula, in the western half of its distribution. It is found from sea level to altitudes of 2,000 metres, making it an adaptable species, tolerant of both drought and salt-laden winds.

Its common name proves a very accurate description; holm is an Anglo-Saxon word for holly. The thick, spiny, sclerophyllous leaves are an adaptation to the hot, dry Mediterranean climate, preventing excess evapotranspiration from the leaf surfaces, and browsing by mammals. However, leaves vary greatly in shape, even in the same tree. Following wildfire events, the holm oak is capable of regenerating from the base of the trunk, due to concentrations of meristematic cells that produce new buds.

Holm oak is used widely in parkland plantings as an ornamental feature, either as a specimen tree or trimmed as a restricted topiary piece; they can also be coppiced on rotation to mimic the effects of natural fire damage. The tree has become widely naturalised in Britain, particularly in the warmer southern counties. Seeds of this and other oaks are classified as recalcitrant, being intolerant of desiccation. They cannot therefore be dried and stored, as with many other plant species. Seeds must be sown fresh to ensure germination. The high levels of germination in holm oak have raised concerns about its potential as an invasive species.

Commercially, the acorns are favorite fodder for pigs reared for cured ham in Spain, Portugal and Italy. The timber is strong, durable and contains a natural preservative, but is largely underused in favour of the English oak. It is unusual to encounter mature, naturally-occurring specimens, as many oak woodlands are managed as grazing areas, or coppice for the production of firewood. Ancient holm oak forests are still present in Sardinia, where there are trees reputed to be up to 1,000 years old.

Phyllonorycter messaniella, the oak leaf miner, is a prevalent pest of the holm oak. The larvae mine through the leaf tissue, resulting in yellow-brown damage to the upper leaf surface and reduced photosynthetic function.

Further reading

Bean WJ 1976. Trees and shrubs hardy in the British Isles. Vol 3. John Murray.

Dallman PR 1998. Plant life in the world's Mediterranean climates. Oxford University Press.

Omari BE et al. 2003. Resource remobilization in Quercus ilex L. resprouts. Plant and Soil 252: 349-357.

Tom Price