| Description |
As a result of human activities, a considerable part of European vascular plants and their populations are non-native. Since the publication of previous studies summarizing the composition and structure of European alien flora, our knowledge has increased, and new alien plant inventories and updates to existing ones have been published. The aim of our work was to create an overview of currently available inventories in Europe, compare them and identify the main gaps and inconsistencies. We compiled 111 national or regional inventories published up to 2022 for 55 European territories, i.e. countries, selected regions within countries, large islands and archipelagos. Using a standardized methodological approach, we unified taxonomy, nomenclature, residence time, invasion status categories, and origin. At the level of the European species pool, we identified 7,335 alien vascular plant species, which is 1,546 more than in the previous study from 2008. Regarding residence time, 1.5% of plants were considered as archaeophytes, 77.2% as neophytes, 9.3% as archaeophytes in one part and neophytes in another part of Europe, while 12.0% of species had undistinguished alien status. Regarding invasion status, 33.3% of aliens were casual, 36.3% were naturalized, and 14.4% were invasive in at least one European territory; for 5.8% of taxa, the invasion status could not be reliably assessed. At the level of individual territories, archaeophytes and neophytes were recognized in 40.0% of the European territories with data available. Regarding the invasion status, the full categorization was available only for 43.6% of territories, while in 20.0%, only invasive species were listed. We found 114 species reported to occur in more than half of the territories. The most widespread species were Erigeron canadensis , Amaranthus retroflexus , Galinsoga parviflora and Robinia pseudoacacia . Most aliens belonged to the families Asteraceae , Poaceae , Rosaceae and Fabaceae . The highest proportions of alien species in Europe originated from temperate Asia (20.4%), temperate Europe (19.6%) and the Mediterranean region (19.0%). Invasive species originated predominantly from the American continent (22.9%) and temperate Asia (19.7%). We found gaps and significant persisting inconsistencies not only in the recognition of residence time and invasion status across territories but also in contradicting status assignments of individual species. This raises the need for a critical reassessment of species' status across Europe, most notably on the Balkan Peninsula and in north-eastern Europe. Updated and standardized national alien checklists are crucial for reliable analysis of the magnitude, mechanisms and impact of invasions, as well as for risk assessments and management across Europe.
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