The vascular plant flora of the Mediterranean Basin is estimated to include about 25,000 species (22,500 native species), making this region the richest among MTEs in total plant diversity. By comparison, the remaining portions of Europe without mediterranean-type climate regimes cover four times as much area but have only about 6000 vascular plant species.
This large flora in the Mediterranean Basin is a broad mixture of species with disparate evolutionary histories and biogeographic origins. Endemism is high at the species level in the Mediterranean Basin, with a level of about 50%, but no family of vascular plants is strictly endemic to the Mediterranean Basin.
One group of species evolved under subtropical conditions that existed in this region prior to the Quaternary. These include such woody plant genera as Arbutus and Calluna (Ericaceae), Ceratonia (Fabaceae), Chamaerops (Arecaceae), and Laurus (Lauraceae). Another group of taxa represents neo-Mediterranean elements that migrated into the Mediterranean basin after the establishment of a mediterranean-type climate. Examples of woody genera in this group include Amelanchier (Rosaceae), Clematis (Ranunculaceae), and Cistus, Halimium, and Helianthemum (Cistaceae). Three groups of temperate woody elements that evolved after the onset of mediterranean-type climates have been identified. These groups are a mediterranean element evolved in situ in mountain areas and exhibiting high endemism, a desert and cold steppe group of species entering from Africa and the Middle East, and a Holarctic element of species 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.