Biological invasions are one of the main drivers of modern human-induced species losses. Research on the distribution of alien species and their pathways of introduction is essential for understanding and tackling the invasion process. A comprehensive overview on invasive alien plant (IAP) species in Romania is lacking. With this paper, we aim to contribute to filling this gap and to provide a visualization of national patterns regarding plant species invasions, geographical origins and pathways of introductions. Based on plant species occurrence records in the published literature and herbaria we compiled a national database of 102 invasive and potentially invasive alien plant species. We georeferenced 42776 IAP species occurrences and performed an analysis of their spatial patterns. The spatial analyses revealed a biased sampling, with clear hotspots of increased sampling efforts around urban areas. We used chord diagrams to visualize the pathway of introduction and geographical origins of the IAP species, which revealed that species in Romania originate mainly in North and Central America, while the dominant pathway of plant introduction was horticulture. Our results provide an important baseline in drafting management and action plans, as invasive alien plant species represent a priority for the European Union through the Biodiversity Strategy for 2030, and a good starting point for various analyses as the database is further developed and regularly updated.

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"The first list of non-native ornamental plants (nNOP) reported as escaped, aturalised or invasive in Romania was published 15 years ago. Since then, new additions to the non-native ornamental flora of Romania ave been reported, while others plants have changed their status. As ornamental horticulture is one of the most important pathways for non-native plant introduction worldwide, we evaluated nNOP at the national level and updated the previous list in order to contribute to the development of tools for preventing, detecting, monitoring and managing the spread of nNOP. The updated list includes 264 taxa. Most of these are casual (199 taxa), 37 taxa are naturalised, and 28 taxa are invasive. In addition, the following characteristics were analysed: family, native range, life form, abundance in the country reported as number of localities and temporal trends. Non-native ornamental flora of Romania is dominated by American and Asian taxa, phanerophytes, hemicryptophytes and therophytes. The most widespread species is Robinia pseudoacacia, used not only for ornamental purposes, but also for its economic value. Many taxa (108 taxa) occur only in two to ten localities. 78 nNOP have been reported in the last 20 years. Six taxa are species of European Union concern (Ailanthus altissima, Asclepias syriaca, Cabomba caroliniana, Humulopsis scandens, Impatiens glandulifera, Myriophyllum aquaticum) and require special measures to control and mitigate their populations."

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An assessement of the alien plants of Romania was conducted which considered the requirements of Regulation 1143/2014 of the European Union (EU). Thus, available data about the presence, invasiveness, distribution, pathways of introduction and their known impact in the territory of Romania were analysed. We found that of 36 plant species of EU concern, four are already established in Romania and widespread, at least locally or regionally: Ailanthus altissima, Asclepias syriaca, Elodea nuttallii and Impatiens glandulifera. For Humulus scandens there are some reports, but its presence and status require confirmation. Heracleum sosnowskyi and Ludwigia peploides are confirmed for only one location for each species. The presence of Cabomba caroliniana and Myriophyllum aquaticum in Romania is not confirmed. Most of the records are intentional introductions for ornamental purposes. Regarding their invasiveness, given the geographical origin and history of invasion in warmer climate regions (e.g., tropical, subtropical), many of the species listed as being of EU concern do not currently constitute a real threat to Romania, for the time being, but may do in a climate change scenario for the 2070s. Data about the impact of alien plant species and their management in Romania are scattered or completely missing. Coordinated institutional efforts are needed to increase the efficiency of the management of alien species at national and local level. These efforts should include: enhancing the legislation and the capacity of public institutions to manage invasive species, increasing the research interest in the science of this topic and promoting real measures to mitigate, control and remove alien plants.