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Diversity patterns can show congruence across taxonomic groups. Consistent diversity patterns allow the identification of indicator surrogates potentially representative of unobserved taxa or the broader biodiversity patterns. However, the effective use of biodiversity surrogates depends on underlying mechanisms driving the strength of the relationship among taxonomic groups. Here, we explored congruence patterns in community composition among taxa occupying different trophic levels, accounting for abiotic and biotic factors: vascular plants and six groups of ground-dwelling arthropods (pseudoscorpions, spiders, darkling beetles, rove beetles, ground beetles and ants) were chosen as potential indicator surrogates. We evaluated the cross-taxon relationships using Mantel test; subsequently, we investigated if these relationships could partially depend on abiotic drivers, using partial Mantel tests; then, we evaluated the partial contributions of abiotic and biotic drivers in explaining these relationships through a series of variation partitioning analyses. Our results showed that a consistent cross-taxon congruence pattern was evident across almost all group pairs: pseudoscorpions, spiders, ground beetles and vascular plants showed the largest number of significant correlations with other taxa. Environmental gradients resulted as drivers of cross-taxon congruence, shaping composition patterns. However, they were not the only ones. Biotic drivers account for part of cross-taxon congruence among vascular plants and arthropod predators (i.e., pseudoscorpions and spiders, but also ground beetles), as well as among taxa at high trophic levels. Almost all strictly predatory taxa, known as biological control agents, emerged as the best predictors of plant community composition even when the role of environmental factors was considered. Spiders/ants and spiders/ground beetles showed close relationships and congruent composition patterns, irrespective of environmental parameters. Relationships among taxa might be driven by several complex biotic interactions (e.g., non-trophic and trophic interactions, direct and indirect interactions). Bottom-up and top-down forces, consumptive and non-consumptive interactions may play a role in influencing the community composition of taxa and driving the observed relationships. Future studies should broaden knowledge about the role of these forces and interactions in determining the congruence across taxa. The multi-trophic perspective in cross-taxon studies can be promising for identifying biodiversity surrogates and their application in conservation planning.

Despite the importance for scientific and conservation purposes, the knowledge of the Italian territory is far from exhaustive. New chorological data for 87 vascular taxa regarding the central-southern part of Italy and its two main islands (Sicilia and Sardegna) are presented. Among these taxa, Epilobium nummularifolium, Metrosideros excelsa, and Salvinia minima are recorded as casual aliens for the first time in Europe (excluding Azores and Madeira for M. excelsa), while Cyclamen balearicum and Polygala rupestris are reported for the first time and confirmed for Italian native flora, respectively. Furthermore, several taxa are new or confirmed at regional level. Finally, Lathyrus cirrhosus, Urginea fugax, and Linum tenuifolium are excluded from Italy, continental and peninsular Italy, and Sardegna, respectively.