While alien organisms, vascular plants included, are progressively increasing their worldwide impact on habitats, the present research confirms a similar dangerous trend for Calabria, the southernmost and floristically richest region of Italian Peninsula. The set of additional alien taxa here recorded for the vascular flora of Calabria includes: Acacia melanoxylon, Bidens subalternans, Buddleja davidii, Cucurbita moschata, Cyclospermum leptophyllum, Erigeron annuus subsp. annuus, Hesperocyparis glabra, Ligustrum ovalifolium, Mahonia aquifolium, Morus indica, Oenothera speciosa, Prunus serotina, Pyracantha fortuneana, Rudbeckia laciniata, Solanum nitidibaccatum, Sparaxis bulbifera, Tradescantia cerinthoides, Ulmus pumila. These additional 18 taxa bring the total number of alien species from 382 to 400. The most represented biological forms are scapose therophyte and scapose phanerophyte with 5 species (27.8% of the total). The most frequent biogeographic origins of the surveyed species are North America (6 species; 33.3%), followed by Asia and South America both with 4 species (22.2%). The most common habitats hosting the recorded alien taxa are roadsides (8 species; 44.4%), although all surveyed plants have been found in deeply anthropized environments. The altitude of occurrence, extending 3 to 1,286 m a.s.l., together with other ecological data provided, demonstrate the ability of aliens to potentially colonize a wide range of environments in the region.

Recent field investigations, performed across some of the less floristically known sectors of Calabria, have led to the discovery of Salsola tragus and Thymelaea gussonei, two new species for the regional vascular flora. By providing crucial biogeographical and taxonomic remarks, this work aims to contribute to the improvement of the knowledge of the rich, diversified and still poorly known native flora of Calabria. The biogeographical value of these new findings underlines the decisive role of field survey in the enhancement of the information on regional biodiversity, the essential basis for every further ecological study and conservation effort.