Ilex - History

History

The phylogeography of this group provides examples of various speciation mechanisms at work. In this scenario ancestors of this group became isolated from the remaining Ilex when the Earth mass broke away from Gondwana and Laurasia about 82 million years ago, resulting in a physical separation of the groups and beginning a process of change to adapt to new conditions. This mechanism is called allopatric speciation. Over time survivor species of the holly genus adapted to different ecological niches. This led to reproductive isolation, an example of ecological speciation. In the Pliocene, around five million years ago, the formation of the new orogeny diversified the landscape and provided new opportunities for speciation within the genus.

The fossil record indicates that the Ilex lineage was already widespread prior to the end of the Cretaceous period. 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. The laurel forest covered great areas of the Earth during the Paleogene, when the genus was more prosperous. This type of forest extended during the Neogene, more than 20 million years ago. Most of the last remaining temperate 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 the extreme cold and aridity and protected by the oceanic influence.

The genus includes about 400 to 600 species, divided into three subgenera:

• Ilex subg. Byronia, with the type species Ilex polypyrena
• Ilex subg. Prinos, with 12 species
• Ilex subg. Ilex, with the rest of the over 400 species