Ilex, also called holly, is a group of more than 570 types of flowering plants in the family Aquifoliaceae. It is the only living group in that family. Ilex has the most types of any group of woody plants that have separate male and female plants. The plants can be evergreen or deciduous and grow as trees, shrubs, or climbers in tropical and temperate regions around the world. The main example of this group is Ilex aquifolium, which is the common European holly used in Christmas decorations and cards.

Description

The genus is found in temperate and subtropical areas around the world. It includes trees, shrubs, and climbing plants with evergreen or deciduous leaves and small, not very noticeable flowers. In the past, during the Tertiary period, the genus had a larger range, and many species live in laurel forest environments. These plants grow from sea level up to more than 2,000 meters (6,600 feet), including species in high mountain areas. The genus consists of small, evergreen trees with smooth, hairless, or slightly hairy branches. These plants grow slowly, with some reaching up to 25 meters (82 feet) in height. The type species is the European holly, Ilex aquifolium, named by Linnaeus. Plants in this genus have simple, opposite glossy leaves, often with spiny edges. The flowers are small, greenish white, and have four petals. Most species are dioecious, meaning male and female flowers grow on separate plants. The flowers of these plants are very similar, and a flower preserved in amber shows that they have changed little in at least 38–34 million years.

The small fruits of Ilex, often called berries, are technically drupes. They can be red, brown, black, or rarely green or yellow. Each fruit contains up to ten seeds inside. Some species, like the cultivar 'Nellie R. Stevens', produce fruits without needing pollination. These fruits ripen in winter, creating a bright red contrast against the glossy green leaves. For this reason, cut branches, especially from I. aquifolium, are commonly used in Christmas decorations. The fruits are slightly toxic to humans and may cause vomiting or diarrhea if eaten. However, birds and other animals eat the fruits and help spread the seeds. This can cause problems, as seen along the west coast of North America, from California to British Columbia. English holly (Ilex aquifolium), grown commercially, is spreading rapidly into native forests. It thrives in shaded areas and outcompetes native plants. The plant is listed on the Washington State Noxious Weed Control Board's monitor list and classified as a Class C invasive plant in Portland.

Etymology

The Latin word "Ilex" refers to the holm-oak or evergreen oak (Quercus ilex). Even though scientists classify Ilex as holly, in Britain during the 19th century, the term "Ilex" was still used for both the oak and the holly. This may have happened because the leaves of these plants look somewhat similar. In everyday language, the word "holly" usually describes the plant Ilex aquifolium, especially its stems with berries used for Christmas decorations. Over time, "holly" has come to refer to the entire Ilex genus. The word "holly" is believed to have developed from Old English "hole(ġ)n," Middle English "Holin," and later "Hollen." The French word for holly, "houx," comes from the Old Low Franconian "*hulis" (Middle Dutch "huls"). These words are connected to Old High German "hulis" and "huls," as well as similar terms in Low German and Low Franconian, such as "Hülse" or "hulst." These Germanic terms appear to be related to words for holly in Celtic languages, like Welsh "celyn," Breton "kelen(n)," and Irish "cuileann."

Many Romance languages use the Latin term "acrifolium," meaning "sharp leaf," such as Italian "agrifoglio" and Occitan "grefuèlh." The usual Latin name for the European holly is "aquifolium," meaning "pointy leaf," which is thought to come from the same root as the word "acutus." However, "acrifolium" is believed to be the original form of the word.

History

The way this group of plants spread across the Earth shows how new species can form. Long ago, about 82 million years ago, the ancestors of this group became separated from other Ilex plants when the Earth split into two landmasses called Gondwana and Laurasia. This physical separation started a process where the plants changed over time to survive in their new environments. This process is called allopatric speciation. Over time, different species of holly adapted to live in various habitats, which led to them no longer being able to reproduce with each other. This is an example of ecological speciation. During the Pliocene, about five million years ago, the formation of mountains created new areas where holly species could develop further.

Fossils show that the Ilex family was already found in many places before the end of the Cretaceous period. The oldest known pollen from Ilex comes from the Turonian period in the Otway Basin of Australia. The earliest fossil of a holly fruit was found in central Europe from the Maastrichtian period. Using a method called the molecular clock, scientists estimate that the common ancestor of most living Ilex species existed during the Eocene period, about 50 million years ago. This suggests that older Ilex species are now extinct. This ancestor likely lived in subtropical East Asia, and the current worldwide spread of Ilex species happened later through migration. Ilex sinica appears to be the oldest surviving species of the group. During the Paleogene period, laurel forests covered large areas of the Earth, and the Ilex genus was more widespread. These forests expanded further during the Neogene period, more than 20 million years ago. Most of the last temperate broadleaf evergreen forests are believed to have disappeared around 10,000 years ago at the end of the Pleistocene. Many species that needed very specific living conditions became extinct because they could not move past geographic barriers, but others survived in protected areas such as coastal regions, islands, and mountain ranges that were far from extreme cold and dryness and were shielded by ocean influences.

Range

The genus is found in many different climates around the world. Most species live in the tropics and subtropics. They are also found in temperate regions worldwide. The greatest variety of species is in the Americas and Southeast Asia.

Ilex mucronata, once the type species of Nemopanthus, is native to eastern North America. Nemopanthus was considered a separate genus with eight species. It belongs to the family Aquifoliaceae and has been moved to the genus Ilex based on molecular data. It is closely related to Ilex amelanchier.

In Europe, the genus is represented by one species, the traditionally named holly Ilex aquifolium. In continental Africa, this species and Ilex mitis are found. Ilex canariensis from Macaronesia and Ilex aquifolium share a common ancestor in the laurel forests of the Mediterranean. Australia, which became isolated early in its history, has Ilex arnhemensis. Out of 204 species in China, 149 are endemic. A species important for economic reasons in Spanish-speaking countries and Brazil is Ilex paraguariensis, also known as Yerba mate. Many hollies have evolved to be found only on islands and small mountain ranges. These plants are very useful, but many are now becoming rare.

Ecology

Tropical species are often in danger because of habitat loss and overuse. At least two types of Ilex plants have gone extinct recently, and many others are struggling to survive.

These plants are a key food source for many bird species and are also eaten by other wild animals. In autumn and early winter, the fruits are hard and not tasty. After freezing or frost several times, the fruits become softer and have a milder taste. During winter storms, birds often find shelter in hollies, which offer protection from predators (because of the spiny leaves) and provide food. The flowers are sometimes eaten by the larvae of the double-striped pug moth (Gymnoscelis rufifasciata). Other moths whose larvae feed on holly include Bucculatrix ilecella, which only eats hollies, and the engrailed (Ectropis crepuscularia).

Toxicity

Holly contains substances such as caffeic acid, caffeoyl derivatives, chlorogenic acid, quercetin, quinic acid, kaempferol, tannins, rutin, caffeine, theobromine, and ilicin. Holly berries can cause vomiting and diarrhea. They are especially dangerous if children accidentally eat them because the bright red berries may attract them. Eating more than 20 berries could be deadly for children. Holly leaves, if eaten, can cause diarrhea, nausea, vomiting, and problems with the stomach and intestines. Holly plants can be harmful to pets and livestock.

Uses

Some holly species have leaves that are used by certain cultures to make tea. These species include Yerba mate (I. paraguariensis), Ilex guayusa, Kuding (Ilex kaushue), Yaupon (I. vomitoria), and others. Leaves from other holly species, such as gallberry (I. glabra), are bitter and can cause vomiting. In general, not much is known about differences between species in terms of their chemical makeup or potential harm.

Holly berries are fermented and distilled to create a type of clear alcohol called eau de vie.

Many holly species are commonly used as ornamental plants in temperate and European gardens and parks. Examples include:
• I. aquifolium (common European holly)
• I. crenata (box-leaved holly)
• I. verticillata (winterberry)

Hollies are often planted as hedges because their spiny leaves make them hard to cut through, and they grow well when trimmed and shaped. Hundreds of hybrids and special varieties have been created for gardens. Examples include "Highclere holly" (Ilex × altaclerensis, a mix of I. aquifolium and I. perado) and "blue holly" (Ilex × meserveae, a mix of I. aquifolium and I. rugosa). Varieties such as I. × meserveae Blue Prince ('Conablu') and Blue Princess ('Conapri') have received the Royal Horticultural Society's Award of Garden Merit. Another hybrid is Ilex × koehneana, with the variety 'Chestnut Leaf'.

European holly (Ilex aquifolium) is often associated with Christmas and is sometimes called Christ's thorn. In many Western Christian traditions, holly is used as a Christmas decoration, especially in wreaths and on holiday cards. Since medieval times, holly has had Christian symbolism, as shown in the Christmas carol "The Holly and the Ivy," where holly represents Jesus and ivy represents the Virgin Mary.

In heraldry, holly is used to symbolize truth. Stord Municipality in Norway includes a yellow holly twig in its coat of arms.

Druids believed that holly leaves protected people from evil spirits and wore holly in their hair.

In the Harry Potter books, holly is the wood used to make Harry's wand.

In some Wiccan traditions, the Holly King is one form of the Sun God. He is born at midsummer and rules from Mabon to Ostara.

In the Irish language, the phrase "mac cuilinn" means "son of holly." Common English versions of this phrase include surnames like McCullen, McCullion, McQuillan, and MacCullion.

Gan Mao Ling (感冒灵) is a Chinese herbal medicine said to help with early symptoms of colds or flu. A main ingredient is the root of the Ilex plant. It is widely used in Traditional Chinese Medicine. The ingredients include: Ilex root, Gang Mei Gen Euodia leaf, San Cha Ku Chrysanthemum flower, Ju Hua Vitex herb, Huang Jing Cao Isatis root, Ban Lan Gen Lonicera flower, and Jin Yin Hua.

Gallery

• Ilex anomala
• A contorted hedgehog holly, Ilex aquifolium 'Ferox'
• Ilex chinensis
• Ilex pedunculosa
• Ilex rotunda
• Ilex yunnanensis
• Ilex × meserveae
• Ilex pernyi from western China