Ilex aquifolium – December 23rd 2024 – Holly
There is no finer sight in these winter months than a Holly tree in full fruit. No wonder we gather it for decorating our homes at Christmas. It brings good cheer when days are short and skies are grey.
Holly tree with fruits in winter. Image: Chris Jeffree.
Holly belongs to the Aquifoliaceae, a family of around 400 species, nearly all of them belonging to the genus Ilex. Those we know best usually have spiny leaves (our own Ilex aquifolium and the American Holly, Ilex opaca). These two hollies are very similar and both are used as decorations to enhance the merry-making of Christmas. It is reckoned that in pre-Christian times, the Romans used holly in the celebrations of Saturnalia (a time of winter gift-giving, feasting and bucolic celebration).
Holly berries with snow. Image: Chris Jeffree.
There is a strong connection of holly with Christianity, as the spines are said to represent the crown of thorns worn by Jesus and the berries are the drops of his blood. Thus, they are brought into churches. We have the verse by John Betjeman:
Likewise, in the hymn of the Anglican church we have:
The ambiguity of the last line may have been deliberate. The ‘crown’ might refer to the crown of thorns on the head of Jesus, or perhaps to holly’s pre-eminent status as a king of the woodland species (more about that later).
Side-view of leaves to show alternation of spines. Image: Chris Jeffree.
Ilex aquifolium grows as an evergreen shrub or a tree up to 22 metres tall. The leaves are dark green, glossy, without hairs. A thick waxy cuticle makes the leaves tough and stiff – they can never wilt even when dry. The extreme spininess is a variable character. Often it is the lower leaves that are spiny whilst those at the top of the tree lack spines. Presumably spines protect against hungry ungulates, and so are more useful in the lower part of the canopy. There is evidence that spininess can be stimulated by grazing pressure (Obeso 1997). Over the centuries many cultivars (perhaps 100) have been described with leaves that vary in spininess and colour; these cultivars have been propagated from ‘sports’ i.e. mutations, which have occurred naturally.
Variation in the degree of spinescence on a single tree. Image: Chris Jeffree.
There are separate male and female trees, although sex-changing has sometimes been recorded. Flowers and berries are borne on female trees. The flowers open in May or June; they are white, fragrant, about 6 mm in diameter, on second-year wood. They are clustered in the axils of leaves. Insects are attracted to the fragrance; pollination is mostly by bees, often the honey bee Apis mellifera. The fruit is the familiar ‘berry’ which, botanically speaking, is technically not a berry but a drupe. Fruits are taken by thrushes, blackbirds, finches, fieldfares and redwings, and thus widely dispersed in bird-droppings.
Flowers of the holly Ilex aquifolium. Left, male; right female. Images: Chris Jeffree.
The wood is fine-grained, dense and white. Many uses of this material have been found and sometimes it is dyed as a substitute for ebony. Two of the more esoteric historic uses are in the making of bagpipes and magic wands. Holly is one of the finest woods for turning on a lathe, and thus there were many less esoteric uses than pipes and wands, such as the manufacture of bobbins for the textile industry in Lancashire, the crafting of scientific instruments and printing blocks.
In post-glacial times, Britain was colonised by many species from Europe before the sea level rose about 7,000 years ago to isolate the British Islands. Ilex aquifolium was one of the last trees to arrive, along with beech, hazel and hornbeam, although it had been present during earlier interglacial periods. Its pollen record in England shows a steady increase during climatic warming between the Sub-Boreal and Sub-Atlantic (4,700 – 2,700 years before the present, roughly co-inciding with ‘the Bronze Age’).
Current habitats, according to the BSBI Atlas 2020 are:
“….deciduous woodlands and wood-pasture, especially those on acidic soils in which Fagus sylvatica and Quercus predominate; often a frequent or locally dominant undershrub but rarely dominating the canopy. …. It is also found in scrub and hedgerows, and on ledges of acidic cliffs, and is often planted in amenity areas and parkland”.
Holly tree, evidently once part of a hedge marking field boundaries. It was common for hedge-cutters to leave the holly trees to grow, either because of superstitious beliefs or to ensure there were some berries for Christmas. Image: Chris Jeffree.
Holly doesn’t like cold. Its distribution pattern suggests the average temperature of the coldest month (normally January) does not fall below -0.5 oC and the warmest month (July) must not fall below 12.8 oC. This excludes it from most of Scandinavia, but it grows in the northerly parts of the British Isles and also in the most exposed parts of the west coast. However, Mitchell (1982) considers it not a true native in Caithness, Orkney and Shetland where the July mean temperature is close to 12 oC.
Insects on holly. Left, Holly Blue butterfly (Celastrina argiolus) which has its first brood on flower buds of holly and its second brood on Ivy; right, an unidentified bug. Images: Chris Jeffree.
Few species are as tolerant to soil conditions. Ilex aquifolium grows on many types of soil, from acid heathland podsols to chalky soil and cracks in limestone.
In historic times it formed substantial woodlands, with large trees forming pure stands from which valuable timber was cut. In some places it was truly ‘the king of trees’. Peterkin and Lloyd (1958) cite examples of this from the Lake District, Northumberland and beside the rivers Dee and Findhorn in Scotland. It is said to have been the second most abundant charcoal in Roman pottery. It was grown in monastic gardens in Chaucer’s time (Harvey 1981). Chaucer evidently knew his trees: I was surprised to find that in later life he held the position of Deputy Royal Forester at North Petherton, Somerset.
The British and Irish distribution shows Ilex aquifolium to be present almost everywhere except for montainous areas and the extreme north. From BSBI/Maps.
Almost all pure holly woodlands are gone. In modern times holly occurs mostly as isolated trees or shrubs, often forming part of the understory of woodlands, as a component of hedges or as garden specimens. One likely cause of historic decline was the over-zealous collection of the bark to make birdlime, a glue used by huntsmen-of-old, smeared on the branches of trees to catch small birds. The manufacture of birdlime is described in Gerard’s Herbal of 1597 as follows:
“There is made of the smooth bark of this tree or shrub, birdlime, which the birders and country men do use to take birds with: they pull off the bark, and make a ditch in the ground, specially in moist, boggy, or soggy earth, whereinto they put this bark, covering the ditch with boughs of trees, letting it remain there till it be rotten and putrefied, which will be done in the space of twelve days or thereabout: which done, they take it forth, and beat in mortars until it be come to the thickness and clamminess of lime: lastly, that they clear it from pieces of bark and other filthiness, they do wash it very often: after which they add unto it a little oil of nuts, and after that do put it up in earthen vessels”.
Holly was used from the 12th to the 18th Century to feed livestock in the winter, especially in Cumbria, the Welsh Borders and the Pennines. Branches would be cut from the tree and laid down on snow-covered fields. Hungry sheep and cattle did not mind the spines.
The abundance of folklore concerning holly is further evidence that it must have been very common. Several pages of country tales from England, connected with witches, farmers and livestock, are to be found in Mabey (1996).
Ilex aquifolium is recorded in North America, where it is called English Holly, presumably brought in by early European settlers. Likewise, it is common in SE Australia and in New Zealand.
The genus Ilex contains many species that are medicinal or used in drinks. Ilex paraguariensis is used to make a popular caffeine-containing tea: yerba maté. From the tropical botanic garden in Xishuangbanna, China, Yao et al. (2022) have compiled a comprehensive review of the worldwide uses of Ilex. This easy-to-read article can be freely downloaded.
Publications consulted
Harvey J (1981) Mediaeval Gardens. Batsford, London.
Mabey R (1996) Flora Britannica. Sinclair-Stevenson, London.
Mitchell A (1974) a field guide to trees of Britain and Northern Europe. Collins, London.
Obeso JR (1997) The induction of spinescence in European holly leaves by browsing ungulates. Plant Ecology 129, 149–156. https://doi.org/10.1023/A:1009767931817
Peterken GF and Lloyd PS (1967) Ilex aquifolium L. Journal of Ecology 55, 841-858. https://www.jstor.org/stable/2258429
Yao X et al (2022) Utilization of the Hollies (Ilex L. spp.) Forests 13, 94 https://doi.org/10.3390/f13010094
©John Grace
