Quercus ilex, the Holm Oak or Holly Oak is a magnificent broad-growing evergreen tree, native to Southern Europe and naturalised in parts of Southern England. It has dark-green, shiny, lance-shaped leaves, spiky like a holly when young but losing this characteristic with age on all but the lower or new branches. A majestic architectural specimen tree it is also probably the most useful of the broadleaf evergreens for creating a windbreak, particularly in coastal areas. Its resistance to salt spray and strong winds has made it a favourite amongst exotic gardeners in the south-west seeking to establish shelter belts for large gardens although its usefulness in providing protection should not be overlooked for the smaller-scale garden.

The tough thick glossy leaves of Quercus ilex, which - unlike most oaks - are unlobed, have a silvery-brown, somewhat downy underside, and are adapted to reduce transpiration loss in the hot Meditarranean climate. Retained over the winter, much of the old foliage falls in the heat of the summer but not before it has been replaced by new growth, a pale silvery-white foliage which is followed by the male yellow male catkins.

The Holm oak is one of several trees associated with the the cultivation of the Black (Tuber melanosporum) or Perigord truffle, with which it grows in a symbiotic relationship, assimilating phosphorus through the mycorrhizal growths produced by the truffle in the tree's roots and supplying sugars in return to the truffle.

It enjoys a chalky alkaline soil and full sun although it tolerates some shade. Hardy and naturalised in the south over chalk grasslands and lowland heaths, Quercus ilex tends to tolerate the harsher conditions of Scotland and Northern England by dropping its leaves in the winter.