The invasion history of Ambrosia psilostachya (Asteraceae) in Italy: first record and distribution over more than one century

Ambrosia psilostachya (Asteraceae) is a perennial ragweed native to North and Central America, introduced to Europe at the end of nineteenth century. Likely to have been accidentally introduced, the species spread in several countries. For a long time, its invasion history has been overlooked mainly due the frequent misidentifications with other ragweeds, mostly with A. maritima, the only species of the genus Ambrosia native to the Old World. This study reconstructs the invasion history of A. psilostachya in Italy through an extensive review of herbarium specimens, literature and field data. According to our research, A. psilostachya was probably introduced to Italy in the first half of nineteenth century, but the first record in the wild dates back to the beginning of twentieth century on the Tyrrhenian coastline. Over the years, A. psilostachya spread along the peninsula becoming common along rivers and coastal dunes, especially in habitats characterized by sandy soils. Its massive occurrence along sandy coastal systems should be considered an urgent call to investigate this species and its impacts more deeply. The species could represent a relevant threat to native flora especially on sandy soils as well as to human health due to its allergenic pollen.