[5] The species are evergreen or deciduous trees, shrubs, and climbers from tropics to temperate zones worldwide.

The type species is Ilex aquifolium, the common European holly used in Christmas decorations and cards.

It includes species of trees, shrubs, and climbers, with evergreen or deciduous foliage and inconspicuous flowers.

[2] Plants in this genus have simple, alternate glossy leaves, frequently with a spiny leaf margin.

Along the west coast of North America, from California to British Columbia, English holly (Ilex aquifolium), which is grown commercially, is quickly spreading into native forest habitat, where it thrives in shade and crowds out native species.

It has been placed on the Washington State Noxious Weed Control Board's monitor list, and is a Class C invasive plant in Portland.

[13][14] The name "holly" in common speech refers to Ilex aquifolium, specifically stems with berries used in Christmas decoration.

[16] [17] The French word for holly, houx, derives from the Old Low Franconian *hulis (Middle Dutch huls).

[18] Both are related to Old High German hulis, huls,[19] as are Low German/Low Franconian terms like Hülse or hulst.

[20] Several Romance languages use the Latin word acrifolium, literally "sharp leaf" (turned into aquifolium in modern time), hence Italian agrifoglio, Occitan grefuèlh, etc.

In the Pliocene, around five million years ago, mountain formation diversified the landscape and provided new opportunities for speciation within the genus.

[22] Based on the molecular clock, the common ancestor of most of the extant species probably appeared during the Eocene, about 50 million years ago, suggesting that older representatives of the genus belong to now extinct branches.

Most of the last remaining temperate broadleaf evergreen forests are believed to have disappeared about 10,000 years ago at the end of the Pleistocene.

Many of the then-existing species with the strictest ecological requirements became extinct because they could not cross the barriers imposed by the geography, but others found refuge as a species relict in coastal enclaves, archipelagos, and coastal mountains sufficiently far from areas of extreme cold and aridity and protected by the oceanic influence.

A species which stands out for its economic importance in Spanish-speaking countries and in Brazil is Ilex paraguariensis or Yerba mate.

Having evolved numerous species that are endemic to islands and small mountain ranges, and being highly useful plants, many hollies are now becoming rare.

During winter storms, birds often take refuge in hollies, which provide shelter, protection from predators (by the spiny leaves), and food.

They are especially dangerous in cases involving accidental consumption by children attracted to the bright red berries.

The sharpness of the leaves help to recall the crown of thorns worn by Jesus; the red berries serve as a reminder of the drops of blood that were shed for salvation; and the shape of the leaves, which resemble flames, can serve to reveal God's burning love for His people.

Combined with the fact that holly maintains its bright colors during the Christmas season, it naturally came to be associated with the Christian holiday.