On the presence of Xanthium ser. Glabrata in Italy and in the Mediterranean basin

Xanthium ser. Glabrata (=X. chinense) is native to Central America and southeastern North America, and in recent times it has been introduced in other parts of the world, where in some cases it has become an invasive weed. It has sporadically been observed in Europe and in the Mediterranean area, mostly as a casual introduction and there is almost no evidence of stable populations. In Europe, other two species of X. sect. Xanthium are present: the native X. strumarium and the introduced X. orientale. A specimen in the herbarium of the University of Catania resembled morphologically X. chinense. It was collected in the Ciane River (southeastern Sicily) and was identified as X. strumarium. We used target enrichment of nuclear genes and the reconstruction of complete plastid genomes, along with phylogenetic methods, to ascertain the taxonomic placement of the specimen. The specimen was confirmed to belong to X. chinense and represents the first record of the species in the Italian territory. With a brief survey in important European herbaria, we were able to identify other specimens belonging to the species in other Mediterranean countries. Further studies are needed to confirm the presence of X. chinense populations in the Mediterranean and evaluate its invasion status.