The history of Xanthium genus research in a protected area in European Russia (Mordovia State Nature Reserve) has been reviewed based on available data (herbarium collections, publications, archive of Chronicles of Nature). We found that X. strumarium was the only species, which has been mentioned in the Mordovia State Nature Reserve since 1939. However, the overview of available data allowed us to conclude that all Xanthium plants found in this protected area to date belong to Xanthium orientale, an invasive alien species.