Invasive or threatened? The decline of the old‐world Xanthium strumarium (Asteraceae ) in Italy based on herbarium records, ESF1

Abstract

Müller-Kiefer, J. & Tomasello, S.: Invasive or threatened? The decline of the old-world Xanthium strumarium ( Asteraceae ) in Italy based on herbarium records. — Fl. Medit. 32: 17-24. 2022. — ISSN: 1120-4052 printed, 2240-4538 online. Xanthium is a taxonomically intricate genus of the sunflower family ( Asteraceae ). In Italy, two species of Xanthium sect. Xanthium are present: the native X. strumarium and then introduced X. orientale . In this study, we assess changes in relative frequency of these two species in Italy based on herbarium records. Based on our analyses, we could observe a strong decline of the native X. strumarium in Italy, started approximately one hundred years ago. Since then, this species has become extremely rare and more effort should be spent to investigate its actual distribution range and potential extinction risk in Italy. This study also demonstrates the importance of herbaria to address ques-tions regarding the dynamics in relative frequency and distribution of competing native and introduced species.