Quercus ilex L.

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Credits

Allen Coombes & Roderick Cameron (2021)

Recommended citation
Coombes, A. & Cameron, R. (2021), 'Quercus ilex' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/quercus/quercus-ilex/). Accessed 2021-10-17.

Genus

Common Names

  • Holm oak
  • Holly oak

Synonyms

  • Quercus gramuntia L.

Other taxa in genus

Glossary

linear
Strap-shaped.
lignotuber
Woody tuber developed in the axils of the cotyledons or the first few leaf pairs. Common in Eucalyptus where they provide a means for regeneration after a fire.
asl
Above sea-level.
dbh
Diameter (of trunk) at breast height. Breast height is defined as 4.5 feet (1.37 m) above the ground.
epidermis
Outermost layer of cells (e.g. covering leaves).
herbarium
A collection of preserved plant specimens; also the building in which such specimens are housed.
pendent
Hanging.
section
(sect.) Subdivision of a genus.

Credits

Allen Coombes & Roderick Cameron (2021)

Recommended citation
Coombes, A. & Cameron, R. (2021), 'Quercus ilex' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/quercus/quercus-ilex/). Accessed 2021-10-17.

Evergreen tree or shrub, 15–30 m in height, to over 2 m dbh, especially where soil is sufficiently moist or where it benefits from a maritime climate. Crown is broad, domed, with ascending branches and often with low stems, trunk short and thick. It can also grow as a flattened, suckering shrub. Bark is thick, tough, greenish-dun or blackish, shallowly cracked into small, square thin plates. Young shoots covered with dense, grey tomentum, which often persists until the second year. Buds small, round or ovoid, tomentose, with stipules that are quickly shed. Leaves very variable, generally lanceolate to oblong-lanceolate or oval, 4–12 cm long × 1–6 cm wide, thick but not rigid, rounded or cuneate at the base, pointed. Leaf margins are wavy or sinuate, sometimes entire, sometimes (especially young leaves or on young trees) dentate, spinose, or serrate. Leaves emerge with both surfaces covered with whitish pubescence, which soon falls away entirely from the upper surface leaving it a shiny blackish-green; on the underside the pubescence turns grey or tawny and persists until the fall of the leaf; with 7–14 pairs of secondary veins, petiole pubescent, 1–2 cm long. Leaf lifespan ranges from less than 1 year to 4 years, depending on leaf position and environmental factors. Catkins dense and pendulous, 4–7 cm long, pale green, opening in a mass of yellow stamens. Acorn borne on a downy peduncle, 0.8–5 cm long, singly or in groups of up to three, ripening in the first year, nut usually ovoid, 15–35 mm long × 8–18 mm wide, hemispherical cupule up to 20 mm wide, light green with appressed scales, enclosing one third to one half of the nut. Acorns ripen November–January (Southern Europe). (de Rigo & Caudullo 2016, Lamant 2010).

Distribution  AlbaniaAlgeriaFrance West and South Greece including the Aegean Isles, Samos, W & C Crete, and Karpathos ItalyJordanNorth MacedoniaMaltaPortugalSerbiaSpain North SwitzerlandTurkey W & N Anatolia, Aegean Isles including Inmroz

Habitat Quercus ilex is generally found in three kinds of vegetation communities: a) matorral vegetation in cold semi-arid climates at high altitudes (Spain, France), in association with Juniperus thurifera; b) matorral or arboreal pre-forest, where it grows in isolation or in clumps, often associated with conifers, typically Pinus halepensis; and c) sclerophyllous woods and maquis vegetation where Q. ilex dominates, associated principally with Olea europea subsp. sylvestris, Ceratonia siliqua, Q. suber, Arbutus unedo, Phillyrea angustifolia, Rhamnus alaternus, and Pistacia terebinthus. This last community is the most widespread evergreen woodland in the Mediterranean region. The species has a wide altitudinal range from sea level up to 1800 m in southern Spain and in France. In other places, the species elevation range is more limited and not as extreme.

USDA Hardiness Zone 7

RHS Hardiness Rating H4

Conservation status Least concern (LC)

Taxonomic note Quercus ilex subsp. refugiorum is an unpublished name given to plants growing on sea cliffs in the region of Biokovo, Croatia. Plants at Chevithorne Barton grown from seed distributed under this name or its var. subtillima have proven to be typical Q. ilex. Several plants are grown at the Howick Arboretum as Q. ilex subsp. refugiorum. Western Mediterranean populations formerly treated as Quercus ilex var. ballota, or Q. ballota, are described under the entry for Q. rotundifolia. Quercus gramuntia was considered a valid species for quite some time following its publication in the first edition of Species Plantarum (1753). Linnaeus followed Magnol’s diagnosis of an oak discovered in the woods near the Domaine de Grammont outside Montpellier, France, distinguished by its rounded and spiny leaves (Magnol 1676). A specimen of this origin was preserved in the Linnaean herbarium. Sir James Smith, who acquired the herbarium, was of the opinion that Linnaeus had based his description mistakenly on another Magnol specimen that was not distinct from Q. ilex. Smith published an amended description in Rees’ Cyclopaedia (1819), apparently based on a living tree, noting that the species was cultivated in England in 1730. His description focuses on aspects that might distinguish the species, depicting the leaves, for example, as ‘very much undulated at the margin, their deep broad spinous teeth pointing every way.’ It later seems to have been associated with what would be accepted as Q. rotundifolia, formerly Q. ilex var. ballota. Captain S.E. Cook described an evergreen oak found in Spain, with edible acorns, which ‘when in perfection, are as good as, or superior to, a chestnut,’ and asserts they must have been the acorns described by Cervantes in his Don Quijote. He notes that the species ‘acquired an unfortunate appellation, that of Gramuntia, from having been observed in a remnant of a wood near Montpelier’ (Cook 1834). According to the Nouveau Duhamel, De Candolle searched in vain for the original trees at Grammont and was of the opinion that the species was in fact Lamarck’s Q. rotundifolia (Loiseleur-Deslongchamps 1819). Bean (1976) speaks of a tree at Kew which resembled Smith’s description of Q. gramuntia, but points out that Q. ilex is polymorphous and concludes that the tree at Grammont was simply an example of the countless minor fluctuations in the species. Elwes and Henry (1906–1913) believed it was ‘probably a form in which the seedling characters are preserved’. It seems clear the name should be put to rest and relegated to the history books.

Quercus ilex has a cultural resonance of exceptional longevity: it is no exaggeration to say that it is one of the most important of European trees. Its prevalence in Mediterranean woodlands would make it so, even without its long history in cultivation. Mediterranean people have valued its umbrageous beauty since at least the Fourth Century BCE, when it was planted in the groves established by philosophers such as Plato and Aristotle, under whose shade scholars studied and debated; the walks under the trees were called peripatoi, and the philosophers who used them were ‘peripatetic’. One such site was Plato’s Academy, which became noted for its beauty (Hobhouse 1992). In Italy the Etruscans evidently valued Q. ilex, regarding at least some specimens as sacred. Pliny wrote about ancient trees in the vicinity of Rome that were believed to have pre-dated the foundation of the city, and it appears in Roman texts as being important for shade, acorns, and the dry leaves were used as sheep-bedding (Loudon 1838). It was to become an integral part of the cultivated landscape of Italy, as is still apparent at many important sites of both classical and renaissance periods. In the Boboli Gardens, Florence, created in the 16th Century for Isabella of Toledo and Cosimo I de Medici, it is used as a primary component of the groves or bosquets, that cover much of the site – and this is true for many other great villa gardens. Loudon (1838) quotes an evidently sarcastically intended quip ‘the eternal ilex’ in reference to its ubiquity in Italian gardens, to which it gives, according to him, a ‘monotonous character.’ In addition it is valuable for its dense, durable wood, but mostly in small pieces as it is apt to deform during drying; it gives good charcoal and has been an important source of fuelwood (Loudon 1838). Older works may have exaggerated its importance as a source of pannage for pigs through confusion with its relative Q. rotundifolia, but Q. ilex remains valued for its acorns in its range further east in the Mediterranean basin (EUFORGEN 2021). For more discerning gastronomes, Quercus ilex is one of the primary mycorrhizal partners of the Black Truffle Tuber melanosporum (Sourzat 2013) and many nurseries across Europe and elsewhere sell young Q. ilex (and other species) inoculated with truffle mycelium for those wishing to produce this valuable crop commercially.

Though a Mediterranean species, it also flourishes in France’s southern Atlantic coast and attains its most attractive dimensions in a maritime climate, which is made evident by its success in cultivation in the United Kingdom (Lamant 2010). Holm Oak was the first non-native oak to be introduced to Britain, where it has been cultivated since the 16th Century: Charles de L’Écluse (Clusius) described two specimens he saw in 1581 in gardens close to London, one of which was old enough to bear acorns (L’Écluse 1601). John Evelyn, in his Sylva (1664), stated that this species ‘thrives manifestly with us [i.e. in Britain]’ and that seedlings he had raised himself ‘have thriven wonderfully, braving the most severe winters, planted either in standards or hedges, which they most beautifully become.’ For Bean (1976b), it is the finest of all evergreen trees – conifers excepted – cultivated in the British Isles, featuring abundant foliage that forms heavy dark masses on the tree. It is diverse in habit, sometimes pendulous, sometimes pyramidal, just as its leaves are infamously protean in size, shape, and toothing. It appears indifferent to soil composition and pH and in the wild it is found on many different soil types. In cultivation it prefers warmth, and rather light and well-drained soils. It is fully hardy in almost all parts of Britain and across the island of Ireland, forming a handsome tree when properly sited. The age of the oldest trees – assumed in some cases to date to the 1600s – and indeed many of only a century or two, demonstrates that the species can cope with extended periods of hard frost and low absolute minimum temperatures, certainly below the -15°C suggested for marginal populations found in southwestern France at 1840 m asl (Lamant & Parmain 2013). The origin of so many old trees in gardens is unknown, but selecting provenances for inferred cold-hardiness may extend its horticultural range further.

The species seems to have fascinated British authors, especially for its ability to maintain its verdure while all about it native oaks are losing theirs. Sir Herbert Maxwell (1915) wrote that it is one of the most ornamental trees that can be grown: “Planted in the open, and given some attention in its youth to keep it to a single leader, it develops into a stately-domed mass of evergreen foliage, quite distinct in character from any other tree that flourishes in the British Isles. It would be sombre, did the leaves not glitter delightfully in sunlight; and in cloudy weather the wind sweeps up their white undersides and sets them all a-twinkle.” Hillier and Lancaster (2014) find it is particularly attractive in June (UK), when tawny or white woolly young shoots and pendent, yellow catkins emerge, standing out against the lush piles of dark green foliage. They report it responds well to clipping and tolerates shade, and makes a rigid hedge resistant to sea winds. Its tolerance of seaside exposure has been long-noted, and it remains in the forefront of all trees for coastal windbreaks. Borrowing from the folklore surrounding Q. ilex’s prickly leaved namesake, we might say that of all the oaks in British gardens, the Holm Oak bears the crown!

Bean (1976b), on the other hand, points out a defect of this species as a tree in tidy gardens: it sheds the previous-year leaves in May/June, making an unsightly mess. He recommends planting ivy underneath to camouflage the litter. In recent years Holm Oaks in Britain have become subject to two leaf miner moths, whose larvae tunnel between the leaf surfaces creating extensive patches of dead epidermis. This can make the trees rather unsightly, though it does not seem to reduce their vigour significantly. Ectoedemia heringella, the Holm Oak Linear Leaf-miner, makes irregular ‘squiggles’ as it feeds on the leaf in late spring, terminating in a dead blotch, while Holm Oak Blotch Leaf-miner Phyllonorycter messaniella tends to eat out a block of tissue between lateral veins. It has three generations per year, so the leaves can be very tattered-looking before they fall (Royal Horticultural Society Advice 2021).

Quercus ilex is known to hybridize with other section Ilex oaks in the wild – e.g. with Q. coccifera (= Q. × auzendei, see entry in TSO) and Q. rotundifolia (= Q. × autumnalis F.M. Vázquez et al.) – and in cultivation, e.g. with Q. leucotrichophora (see entry in TSO). Somewhat unusually, it is also prone to hop the intersectional fence and hybridize with more distant species, notably with Q. robur (= Q. × turneri, the well-known Turner’s oak, see entry in TSO), Q. petraea (= Q. × audleyensis A. Henry), Q. pubescens (= Q. × albescens Rouy ex A. Camus) and Q. pyrenaica (= Q. × subalbescens A. Camus) in section Quercus, and with Q. suber (= Q. × morisii Borzi) in section Cerris.

The Syon Vista at Kew is famously lined with Holm Oaks, intermixed with Q. × crenata and Q. × turneri, but there are no notable specimens in the garden that can compete with the UK & Ireland champions although it has reached 22 m tall there (H. Baldwin pers. comm. 2021). The specimen with the largest girth recorded in the Tree Register (2020) grows in Courtown House in Co. Wexford, Ireland, with a dbh of 4.37 m (2010), followed by one at Fulham Palace, London, with a dbh of 3.88 m (2010). However, both these trees are multi-stemmed. A single-stemmed tree in Westbury Court in Gloucestershire was described by Bean (1976) as ‘the most remarkable specimen in the British Isles’ and reached a dbh of 2.85 m in 2015. The UK & Ireland champion for height stretches to 28.6 m (2017) at Windsor Great Park in Surrey, almost surpassing the 30-m mark set in 1908 by a Holm Oak that used to stand in Kilruddery, Co. Wicklow, Ireland (Tree Register 2020). The Howick Arboretum, England, has a collection of trees of this species raised from seed collected in the Cevennes and French Pyrenees in 1989. Further north, a fine old tree at the Royal Botanic Garden Edinburgh grows by the herbarium building, but is soon to be removed to make way for the construction of a new glasshouse. Several notable specimens grow in south west Scotland, too, including the Dettingen Avenue at Castle Kennedy, planted in the late 18th century. The trees that make up this avenue have a long history of pollarding (T. Christian pers. comm. 2020).

Holm Oak has been in cultivation around the world for centuries. Old specimens can be found in Australia, including a 18-metre-tall tree in Sydney Botanic Gardens, 1.94 m dbh (National Register of Big Trees 2020), and in New Zealand, whose champion in Mt. Eden, Auckland, stood 19.2 m tall × 2.33 m dbh in 2011 (New Zealand Notable Trees Trust 2020). Spanish colonists took their encina with them and trees can be found throughout their former colonies in the temperate zones, from California, where the species has become naturalized (The University and Jepson Herbaria 2020), to Argentina, where a champion tree, over a century old, had reached 25 m in 2001, with 1.68 dbh and a 30-metre crown spread (Laharrague 2001). Its potential for invasiveness, especially as the climate changes, is causing concern among British conservationists, who believe it poses a significant risk to native habitats, especially in coastal areas (Plantlife 2021), and it has been assesed as a risk by the government environmental department Defra (Stace & Crawley 2015). On the Isle of Wight it began colonising St Boniface Down near Ventnor in the mid-20th Century, forming the largest Q. ilex population in northern Europe (Stace & Crawley 2015), but in recent decades there have been continuing efforts to contain it, most recently by introducing browsing goats (National Trust 2021).

The epithet derives from the Latin name for the evergreen oak (the genus Ilex was named for its similarity to the oak), of unknown origin, probably from a lost non-Indo-European language. The Latin root in turn spawned several common names in Romance languages: leccio (Italian), encina (Spanish), azinheira (Portuguese), alzina (Catalan), etc. The common name in English, Holm Oak, derives from an old form of ‘holly’, so here the etymology is inverted, as the oak was named for its similarity to holly.


'Bicton'

Distinguished by its larger, broader leaves, with white felt on the underside. Named by HIllier in 1971 for a remarkable old specimen at Bicton Park in South Devon, England. This may be the plant originally received at Bicton as Q. ilex ‘Crassifolia’ and which is now grown as Q. ilex. Specimens are recorded at Sir Harold Hillier Gardens, England (13.6 m × 48.6 cm dbh, Barry Clarke pers. comm. 2020) and at the Wynkcoombe Arboretum, England (13 m × 35 cm dbh, 2017) (Tree Register 2020).


'Crispa'

An old cultivar of French origin, selected in 1838, still found in some collections. It has small orbicular leaves, 1–2 cm long, margins revolute. Very slow-growing, not exceeding 4 m according to le Hardÿ de Beaulieu & Lamant (2010), but a specimen at Kew had reached 7 m × 66 cm dbh in 2001 (Tree Register 2020).


'Despina'

An evergreen tree selected for its slow and narrow growth. Young shoots densely grey-hairy, as are the underside of the leaves. Leaves lanceolate, up to 8 × 3 cm, dark green above and sparsely hairy. Petiole 0.7–1 cm. A few spines in the upper half of the leaf blade, margin more or less undulate. Leaf apex apiculate. Originated around 1990, raised from seed of Quercus ilex ‘Fordii’ growing at Arboretum Rond Chêne, Esneux, Belgium. The 18-year-old plant had reached only 3 × 1 m in 2010. Named by the originator, André Charlier, after the character Despina from Mozart’s opera Cosi fan tutte (Jablonski 2010).


'Ditha Jung'

Evergreen small shrub, selected for its dwarf pyramidal habit and very small leaves. Leaves small, up to 3 × 0.5 cm, margins spinose-dentate, base obtuse, petiole –3 mm. Leaves glossy dark green above, paler beneath. No fruits observed. The original plant was a chance seedling from acorns collected in 1989 by Gerhard Dönig from Q. ilex growing next to the road from Arco to San Giovanni north of Lake Garda, Trentino/South-Tyrol, Italy, at ~600 m altitude. The original plant, still in a pot, is only 85 cm high and 25 cm wide after 23 years. The thin twigs create an appearance reminiscent of filigree. Named after Mr. Dönig’s mother-in-law. The original plant still grows at the Arboretum Altdorf in Germany (Jablonski 2013a).


'Fordii'

Synonyms / alternative names
Quercus ilex 'Angustifolia'

Small leaves of a peculiarly dark glossy green, 2.5–6 cm long × 1–1.6 cm wide, distinctly narrower than the typical form, the margins wavy and irregularly toothed. Shrubby, dense foliage, of conical habit when young, with principal branches erect. Overall rounded shape, reaching ~10 m. Raised in Lucombe and Pince’s Nursery at Exeter, described in 1843. (le Hardÿ de Beaulieu & Lamant 2010). According to Elwes & Henry (1906–1913), it was named after one of the proprietors of Lucombe and Prince’s Nursery, but it is possible that the Mr. Ford in question was the owner of a neighbouring rival nursery acquired by Lucombe and Prince in 1807 (Greener 2009). The largest specimen in the UK and Ireland grows in Áras an Uachtaráin, the official residence of the President of Ireland in Phoenix Park, Dublin. It measured 15.3 m × 66 cm dbh in 2000. A tree at Sir Harold Hillier Gardens is shorter but boasts a wider girth, measuring 11.0 m × 96.4 cm dbh (at base) in 2020 (B. Clarke pers. comm.). At Kew it has reached 14 m tall (H. Baldwin pers. comm. 2021).


'Fromefield Gold'

New shoots and leaves opening very pale silvery yellow in late April into early May and becoming bright gold up until mid-summer when they become pale green, maturing to pale grey-green. The leaves occasionally show a patch of dark green usually on one side of the midrib and most conspicuous in young leaves.

Selected in about 1988 from seedlings by Dave West of Fromefield Nurseries, Awbridge, Hampshire, UK. The original tree is planted on the nursery boundary and was about 6 m tall in 2020 (Dave West, pers. comm. 2020).


'Genabii'

Leaves very large and leathery, as much as 12 cm long × 6 cm wide, coarsely toothed towards the apex. Distributed by Smith’s Nursery, Worcester, England, before 1870 (Bean 1976; le Hardÿ de Beaulieu & Lamant 2010). The origin of the name is unclear, but there may be a connection to the city of Orléans, France (known as Genabum in Roman times). A specimen at Kew measured 14 m × 57 cm dbh in 2001 (Tree Register 2020) but is now recorded as 18 m tall (H. Baldwin pers. comm. 2020).


'Latifolia'

A large-leaved form like ‘Genabii’, with leaves up to 15.5 cm long × 7.5 cm wide, though not so thick and rigid, toothed towards the apex. An old cultivar, sometimes also called ‘Macrophylla’ (though for the Oak Name Checklist (2020) they are distinct cultivars) (le Hardÿ de Beaulieu & Lamant 2010).


'Matteini'

A selection from Italy notable for its very large leaves that emerge light green with abundant pale hairs, propagated by Matteini Tranquillo Vivai Piante near Pistoia, Tuscany (Matteini Tranquillo 2021). Young trees are in cultivation in the United Kingdom.


'Rotundifolia'

This cultivar mentioned by Bean (1976b) seems to be an incorrect name for Q. rotundifolia. The same applies for Q. ilex ‘Ballota’ (le Hardÿ de Beaulieu & Lamant 2010). These names are not recognized in the Oak Names Checklist (2020).


'Verduzzo'

An evergreen tree, originated around 1974. Young shoots grey-green hairy, as are the underside of the leaves. Leaves lanceolate, up to 5.5 × 2.8 cm, fresh green above and sparsely hairy, margin more or less undulate with a few spines in the upper half of the leave blade. Leaf apex apiculate. Petiole 0.7–1 cm. The whole tree has a fresh green look. Raised from seed collected by the Dalmatian coast opposite the island of Rab in Croatia. Named by the originator, André Charlier, after the fresh green wine called verduzzo from Friuli, Italy. The 20-year-old plant at Arboretum Closerie du Rond Chêne, Belgium, has reached 7 × 4 m (Jablonski 2010).