The vascular plant flora of the Mediterranean Basin includes an estimated 25,000 species, roughly 22,500 of which are native. These numbers make this region the richest among Mediterranean-type ecosystems in total plant diversity. The remaining portions of Europe cover four times as much area but have only about 6,000 vascular plant species.
The Mediterranean Basin’s large flora consists of a broad mixture of species with disparate evolutionary histories and biogeographic origins. Species-level endemism is high at about 50 percent, but no family of vascular plants is strictly endemic to the Mediterranean Basin.
One group of plants evolved under the subtropical conditions that existed in this region prior to the Quaternary. These include woody plant genera such as Arbutus and Calluna (Ericaceae), Ceratonia (Fabaceae), Chamaerops (Arecaceae), and Laurus (Lauraceae). Another group represents taxa that migrated into the Basin after the establishment of its Mediterranean-type climate. Woody genera in this group include Amelanchier (Rosaceae), Clematis (Ranunculaceae), and Cistus, Halimium, and Helianthemum (Cistaceae). Three groups of temperate woody elements evolved on mountains in the area after the onset of the Mediterranean climate regime. These groups are highly endemic, and include a desert and cold steppe group entering from Africa and the Middle East, and a Holarctic element with Eurasian temperate affinities.
Species richness at the scale of 0.1 ha is often remarkably high in lightly grazed or disturbed Mediterranean
woodlands and shrub grasslands, with as many as 119–179 species reported in such stands.