First records of the invasive weed of Union Concern Cenchrus setaceus (Poaceae) in Crete (Greece)

The European Union (EU) has recently published its first list of invasive alien species (IAS) of EU concern to which current legislation must apply. The list comprises species known to pose great threats to biodiversity and needs to be maintained and updated. Horizon scanning is seen as critical to identify the most threatening potential IAS that do not yet occur in Europe to be subsequently risk assessed for future listing. Accordingly, we present a systematic consensus horizon scanning procedure to derive a ranked list of potential IAS likely to arrive, establish, spread and have an impact on biodiversity in the region over the next decade. The approach is unique in the continental scale examined, the breadth of taxonomic groups and environments considered, and the methods and data sources used. International experts were brought together to address five broad thematic groups of potential IAS. For each thematic group the experts first independently assembled lists of potential IAS not yet established in the EU but potentially threatening biodiversity if introduced. Experts were asked to score the species within their thematic group for their separate likelihoods of i) arrival, ii) establishment, iii) spread, and iv) magnitude of the potential negative impact on biodiversity within the EU. Experts then convened for a 2‐day workshop applying consensus methods to compile a ranked list of potential IAS. From an initial working list of 329 species, a list of 66 species not yet established in the EU that were considered to be very high (8 species), high (40 species) or medium (18 species) risk species was derived. Here, we present these species highlighting the potential negative impacts and the most likely biogeographic regions to be affected by these potential IAS.

The objective of this study is to investigate and evaluate the spatial distribution of invasive alien plant species (IAPS) listed in the European Union’s (EU) official register of invasive alien species of Union concern, within the national territory of Ukraine. The research utilizes occurrence records derived from three major open-access biodiversity data repositories: the Global Biodiversity Information Facility (GBIF), iNaturalist, and the Ukrainian Biodiversity Information Network (UkrBIN). In the broader context of Ukraine’s ongoing integration into the EU, aligning national environmental monitoring systems with EU biodiversity policies has become increasingly essential. Ensuring effective monitoring, early detection, and control of these high-risk biological invaders is not only a key element of environmental compliance but also a strategic necessity for safeguarding biodiversity, ecological stability, and food security. The study involves a critical assessment of data quality, completeness, and spatial reliability across the three platforms and includes a comparative evaluation of their usability for generating accurate phyto invasion distribution maps. Invasive alien species (IAS) are widely recognized as one of the primary threats to global biodiversity and ecological balance. Their uncontrolled proliferation can displace native flora, disrupt local ecosystems, alter habitat structures, lead to crop failures, and even trigger negative health outcomes for humans. As of now, Ukraine lacks a nationally adopted list of invasive alien species; therefore, the research adopts the EU List of Union Concern as the reference framework. This list, first established in 2016 and periodically updated (in 2017, 2019, and 2022), currently includes 88 species, of which 41 are vascular plants. An additional amendment proposed in 2025 is expected to include 8 new taxa. The methodological approach of the study is grounded in geospatial data analysis and geoinformation technologies (GIS), with an emphasis on spatial modeling, visualization, and cross-referencing between different data sets. Through the application of spatial analysis tools, the study identifies both confirmed areas of IAPS presence and data-deficient zones, thus providing insight into distribution gaps and monitoring needs. By integrating multiple sources and controlling for reporting biases, the methodology increases the accuracy of detection and minimizes false positives. The resulting distribution maps and geospatial models generated by this research may serve as a foundational resource for developing targeted IAS surveillance strategies, policymaking, habitat restoration plans, and adaptive management measures at both the national and cross-border levels.

In the European Union, regulations and policies have been established to prevent and manage invasive alien species (IAS). The EU Regulation 1143/2014/EC, commonly known as the IAS Regulation, identifies species that pose significant ecological risks, requiring a coordinated response across all EU Member States. These species are classified as “species of Union concern” based on thorough risk assessments and standardized procedures within the EU. Accordingly, species are included in The List of Invasive Alien Species of Union Concern (the Union list), which is subject to regular updates through continuous species evaluations. Currently, the majority of the species on this list are terrestrial and freshwater with few marine species represented. The primary aim of this paper is to review the procedure for the inclusion of species in the Union list. The steps for inclusion are outlined by the IAS Regulation and associated legislation, which govern the risk assessment process. In addition, this paper synthesizes available scientific literature and official documents to summarize the impacts of Plotosus lineatus and Rugulopteryx okamurae on biodiversity and ecosystem services. The potential for future updates to the Union list is currently under consideration, and some marine species are within.

A confusingly labeled water-milfoil of obscure status, known only in cultivation, is here formally described as a new species, Myriophyllum rubricaule Valk. & Duist. sp. nov. This species has fully replaced M. aquaticum in the horticultural trade in Europe since the addition of M. aquaticum to the list of invasive alien species of Union concern (EU regulation no. 1143/2014) in 2016. This manuscript provides a morphological description of M. rubricaule sp. nov., and its distinction from M. aquaticum is further supported by molecular data (chloroplast and nuclear loci).

The list of invasive alien species of European Union concern currently includes 23 plant species. The aim of this study was to assess the potential and importance of introduction pathways for invasive alien plant species in Lithuania, to estimate probability of their establishment and further spread in the country. Analysis of all available information revealed that three species (Asclepias syriaca,Heracleum sosnowskyiandImpatiens glandulifera) currently occur in Lithuania and the latter two are widespread invasive species in the country. The remaining 20 plant species have not been registered in the wild in Lithuania so far. Four of these,Gunnera tinctoria,Lysichiton americanus,Myriophyllum aquaticumandPennisetum setaceum, are occasionally cultivated in gardens or other outdoor areas, and six species, e.g.Cabomba caroliniana,Eichhornia crassipes, Lagarosiphon major, are cultivated in aquaria or other indoor spaces. Naturalization of seven species is unlikely in the country, whereas naturalization of 13 species (Lysichiton americanus,Myriophyllum aquaticum,Pennisetum setaceum, etc.) is plausible. Five of the analysed and still not recorded species are recognized as potentially invasive in Lithuania; the invasion of five species is plausible and that of 10 species is unlikely. The most important pathway of introduction of the analysed species is ornamental gardening. Three species that have not been recorded in Lithuania, but occur in the neighbouring regions of Europe (Elodea nuttallii,Heracleum mantegazzianum,Heracleum persicum) can enter the country by natural means. Importance of permanent studies and surveys on alien plants aiming to ensure early detection and eradication of invasive species is discussed.

This paper is first inventarisation of threatened and invasive vascular plants on the rocky grasslands situated on northern slopes of mountain Matokit and abandoned arable land in vicinity of town of Vrgorac. These sites represent a new site for the Croatian flora. This research was conducted in year 2010 and 2011. We found 11 species of threatened vascular plants that by the Red Book (Nikolić and Topić [14]) and Flora Croatica Database (Nikolić [13]) and 15 invasive species, according to preliminary list of invasive alien species (IAS) in Croatia (Boršić et al. [3]). In this paper the habitat of some species, their distribution in Croatia, life forms and floral elements are described. It was found that threatened species occur exclusively on the rocky grassland habitat, except two species: critically endangered (CR) Papaver argemone and endangered (EN) Hibiscus trionum which were recorded on arable land. All inventoried invasive species, were recorded at the abandoned arable land, except the species Robinia pseudoacacia. Tendency for uncontrolled spread showed species Ailanthus altissima and Ambrosia artemisiifolia. Habitats of rocky grassland are on the stage of secondary succession (healing with the forest), and on the arable land the spread of invasive species exist (due to socio-economic changes: abandonment of agriculture and animal husbandry, and depopulation of the population). The results of these studies are contribution to the distribution map of threatened and invasive species in Croatia, and to the conservation of grassland habitat study area, as well as to preventing of the spread of invasive species.

The Mediterranean Sea is a hotspot for the introduction of non-indigenous species. Among them, invasive alien species can seriously affect the areas they colonize, not only by altering the marine food webs and community structure, but also by harming certain economic activities, such as fishing, tourism, aquaculture and marine infrastructure. Rugulopteryx okamurae is a brown macroalga considered the fourth most harmful species among the 10 most invasive species reported in the Mediterranean; in fact, it has recently been included in the list of invasive alien species of Union concern due to its serious impact on biodiversity and socioeconomic implications. This species was reported for the first time in the Mediterranean in 2002 in Thau Lagoon (France), introduced by the aquaculture of the Japanese oyster Magallana gigas. Since then, this species has spread in both the Mediterranean and Atlantic Ocean with a strong invasive behavior, particularly along the Strait of Gibraltar. Rugulopteryx okamurae was also recently reported for the first time in Italian waters, in the Gulf of Palermo (Sicily). In this study, we report a record of this species further to the east, in the Ionian Sea, where it has not previously been recorded, and provide possible explanations of the spreading and arrival routes in this area. The rapid expansion of R. okamurae is raising concerns; thus, in order to safeguard native communities, it is crucial to keep monitoring this invasive species so that it is possible to regularly update its distribution and follow up on its spread dynamics in the Mediterranean basin.

On 1 January 2015 a new European regulation on invasive alien species entered in force. Key aspects of this regulation are the adoption of a list of invasive alien species which are of European Union concern, the requirement for specific prevention measures, the establishment of early detection and fast eradication measures, and the management of the widely spread invasive alien species. We highlight the potential contribution of the forestry sector to promote the implementation of this regulation. There is a wealth of experience on positive and negative responses of invasive alien species to forestry interventions. This knowledge should be synthesized and further developed to help prevent and manage invasions in forests and adjacent habitats and to minimize the risks of invasive alien species. We thus recommend that decisions regarding the application of the regulation will include actors responsible for, or involved in, the management and use of forests and related semi-natural habitats.

Effective prevention and control of invasive species generally relies on a comprehensive, coherent and representative list of species that enables resources to be used optimally. European Union (EU) Regulation 1143/2014 on invasive alien species (IAS) aims to control or eradicate priority species, and to manage pathways to prevent the introduction and establishment of new IAS; it applies to species considered of Union concern and subject to formal risk assessment. So far, 49 species have been listed but the criteria for selecting species for risk assessment have not been disclosed and were probably unsystematic. We developed a simple method to systematically rank IAS according to their maximum potential threat to biodiversity in the EU. We identified 1,323 species as potential candidates for listing, and evaluated them against their invasion stages and reported impacts, using information from databases and scientific literature. 900 species fitted the criteria for listing according to IAS Regulation. We prioritised 207 species for urgent risk assessment, 59 by 2018 and 148 by 2020, based on their potential to permanently damage native species or ecosystems; another 336 species were identified for a second phase (by 2025), to prevent or reverse their profound impacts on biodiversity; and a further 357 species for assessment by 2030. Policy implications. We propose a systematic, proactive approach to selecting and prioritising IAS for risk assessment to assist European Union policy implementation. We assess an unprecedented number of species with potential to harm EU biodiversity using a simple methodology and recommend which species should be considered for risk assessment in a ranked order of priority along the timeline 2018–2030, based on their maximum reported impact and their invasion history in Europe.

Aquatic ecosystems are particularly vulnerable to the introduction of non-indigenous species (NIS), leading to multi-faceted ecological, economic and health impacts worldwide. The Iberian Peninsula comprises an exceptionally biodiverse Mediterranean region with a high number of threatened and endemic aquatic species, most of them strongly impacted by biological invasions. Following a structured approach that combines a systematic review of available information and expert opinion, we provide a comprehensive and updated multi-taxa inventory of aquatic NIS (fungi, macroalgae, vascular plants, invertebrates and vertebrates) in Iberian inland waters. Moreover, we assess overall patterns in the establishment status, introduction pathways, native range and temporal introduction trends of listed NIS. In addition, we discuss the legal coverage provided by both national (Spanish and Portuguese) and European NIS regulations. We inventoried 326 aquatic NIS in Iberian inland waters, including 215 established, 96 with uncertain establishment status and 15 cryptogenic taxa. Invertebrates (54.6%) and vertebrates (24.5%) were the groups with the highest number of NIS, with Arthropoda, Mollusca, and Chordata being the most represented phyla. Recorded NIS originated from diverse geographic regions, with North and South America being the most frequent. Vertebrates and vascular plants were mostly introduced through intentional pathways (i.e. release and escape), whereas invertebrates and macroalgae arrived mostly through unintentional ways (i.e. contaminant or stowaway). Most of the recorded NIS were introduced in Iberian inland waters over the second half of the 20th century, with a high number of NIS introductions being reported in the 2000s. While only 8% of the recorded NIS appear in the European Union list of Invasive Alien Species of Union concern, around 25% are listed in the Spanish and Portuguese NIS regulations. This study provides the most updated checklist of Iberian aquatic NIS, meeting the requirements set by the EU regulation and providing a baseline for the evaluation of its application. We point out the need for coordinated transnational strategies to properly tackle aquatic invasions across borders of the EU members.

The disproportionately low presence of marine species in the list of invasive alien species (IAS) of Union concern of the European Union (EU) Regulation 1143/2014 does not fully acknowledge the threat they pose to the EU marine environment. In this study, the first EU‐scale Horizon Scanning (HS) focusing on marine alien species was performed, aiming to deliver a ranked list of species that should be of high priority for risk assessment (Article 5 of the EU IAS Regulation). Species absent from or with a limited distribution in EU marine waters were targeted. In total, 363 alien species were initially screened for HS by a panel of experts, including a broad range of taxonomic groups. Species were scored for their likelihood of arrival, establishment, spread, and impact in EU waters. A consensus workshop ranked 267 species, including a subset of 26 prioritized species. These species are considered to be mainly introduced by shipping (fouling and ballast water), via the Suez Canal, and aquaculture activities. The 26 priority species were also scrutinized in terms of feasibility of their management; 18 of them were suggested for performing risk assessments on the basis of the EU IAS Regulation. Since biological invasions are dynamic and connected with accelerated globalization and diversified human activities, we recommend HS to be repeated periodically to review the species already listed and assess new ones.

Modelling Acacia saligna invasion in a large Mediterranean island using PAB factors: A tool for implementing the European legislation on invasive species

The pond slider Trachemy scripta was one of the most commonly exported turtles until the last decade and often released into the wild outside its native range. It was introduced to Europe, Africa, South America and Asia and included on the EU list of 100 World's Worst Invasive Alien Species and the List of invasive alien species of Union concern. The import of the subspecies Trachemys scripta elegans into Europe and Croatia has been banned for some time, but the number of specimens recorded in nature is still increasing. In this paper we present 45 new localities were the species was observed in Croatia, which makes a total of 84 known localities. Most of the records, 58%, are in the Continental biogeographical region and the rest in the Mediterranean. It has not yet been recorded for the Alpine biogeographical region. Most records (42%) come from ponds. Three new sightings of females digging nests, laying eggs and sightings of hatchlings were recorded, suggesting successful reproduction of the species. Further surveys of this alien species in Croatia are needed.

The South African native curly waterweed, Lagarosiphon major (RIDL.) MOSS, is considered as one of the most invasive aquatic plant species worldwide. Due to its economic and ecological impact in freshwater ecosystems, Lagarosiphon major is listed on the EU list of invasive alien species of Union concern. For species included in this list, measures for prevention and management of the further introduction and spread are required according to the EU regulation no. 1143/2014. For an effective implementation, these measures require a comprehensive knowledge on the biology of the target species. In this article, the existing knowledge on the biology of Lagarosiphon major is reviewed and some information about management strategies are given.

Alien Callosciurus squirrels cause severe damage to trees in forests, gardens, and commercial plantations (Jouanin 1986; Setoguchi 1990; Torii 1993; Aprile and Chicco 1999; Gurnell and Wauters 1999). Pallas’s squirrel (Callosciurus erythraeus) originally occurs in eastern India, Bhutan, southeast China, Taiwan, Indochina, and Malaya (Corbet and Hill 1992; Wilson and Reeder 2005). This squirrel was introduced into other countries as an exotic pet. At present, C. erythraeus populations are found in Argentina (e.g., Aprile and Chicco 1999), France (Jouanin 1986; Gurnell and Wauters 1999), and Japan (Ishii 2005; Tamura 2002, 2009; Ikeda et al. 2011). Under law number 78 of the Invasive Alien Species Act (Ministry of the Environment, Government of Japan, 2004: http://www.env.go.jp/nature/intro/index. html), import of C. erythraeus to Japan is strictly prohibited. This species is treated as ‘invasive alien species’ in Japan. Finlayson’s squirrel (C. finlaysonii), which originally occurs in the Indochina Peninsula (Corbet and Hill 1992; Wilson and Reeder 2005), was also introduced to Italy (Bertolino et al. 1999; Currado et al. 1999). Similar to C. erythraeus, C. finlaysonii is thought to cause damage to environments (Bertolino et al. 2004). It is difficult to distinguish this species from C. erythraeus based on external characteristics such as pelage patterns (e.g., Lekagul and McNeely 1988). Based on mitochondrial (mt) DNA control region sequences, Oshida et al. (2007) reported that C. finlaysonii was probably introduced to Hamamatsu, Shizuoka Prefecture, Japan (Fig. 1). They captured eight Callosciurus individuals in Hamamatsu. Of them, seven individuals had haplotypes closely related to that of C. finlaysonii from Laos (two C. finlaysonii haplotypes were detected), and one individual had a C. erythraeus haplotype. Therefore, we expect these two Callosciurus species exist sympatrically in Hamamatsu. Callosciurus finlaysonii, however, is not treated as an invasive alien species in Japan (law number 78 of the Invasive Alien Species Act, Ministry of the Environment, Government of Japan, 2004). Currently this species is treated as unidentified alien species. If the population of C. finlaysonii increases, this species should be added to the list of invasive alien species. To estimate whether C. finlaysonii is increasing, we investigated ratios of C. finlaysonii haplotype and C. erythraeus haplotype in the Hamamatsu population by using mtDNA control region sequences. We discuss the present situation of introduced C. finlaysonii in Hamamatsu. In addition, we compare control region sequences of specimens from Hamamatsu, Laos and Thailand, to identify the origin of introduced C. finlaysonii. The exact origin would be difficult to determine because we do not have sequence data from all C. finlaysonii populations occurring in the Indochina Peninsula. We, however, obtained successfully C. finlaysonii sequences from Thailand and Laos. Identifying whether the Hamamatsu population is more closely related to specimens from Thailand or Laos may help to prevent subsequent introductions of this squirrel into Japan with international legal and political action.