Alien plants and recipient habitats in the Mediterranean Basin: How similar they are?

Biological invasions have become one of the most critical issues related to global change. The aim of this work was to investigate alien plant species invasion levels in different habitats and alien species traits by comparing the naturalized flora in different areas of the same biogeographical region. The locations selected for study were 4 countries across the European Mediterranean basin comprising and east–west gradient, namely Spain, Italy, Greece and Cyprus. Floristic similarity among the 4 countries was found very low, with only 30 species present in all four countries out of the 782 naturalized neophytes. The four alien floras share the same patterns of growth form (mostly herbs), life cycle (mostly perennials) and life form (mostly therophytes, hemicryptophytes and phanerophytes). Artificial habitats and wetlands were the habitats with the highest numbers of naturalized species and display the greatest homogenization in all four countries. Coastal habitats display a lower degree of homogenization but a high frequency of aliens. Dry shrubs and rocky habitats display a lower degree of homogenization and a low frequency of aliens.