Dissecting an endemism hotspot: Spatial phylogenetics of the Iberian angiosperm flora

Background Spatial phylogenetics has emerged as a powerful tool to identify evolutionarily important areas for biodiversity conservation through mapping of phylogenetic diversity and endemism, including centers of neoendemism and paleoendemism. Although Europe is not generally regarded as a major center of plant diversity, recent global spatial phylogenetic studies have identified the Iberian Peninsula, in southwestern Europe, as a center of plant phylogenetic endemism at the global scale. Here we conducted a fine-scale spatial phylogenetic analysis of the angiosperm flora of the Iberian Peninsula and the Balearic Islands, which comprises c. 5,500 native species, more than 1,200 of which are strictly endemic. To this end, we combined a comprehensive distribution database with the most exhaustive megaphylogeny published to date, comprising 53% of the species. Phylogenetic diversity and endemism metrics were calculated, and Categorical Analysis of Neo- And Paleo-Endemism (CANAPE) was conducted, followed by an evaluation of the use of phylogenetic imputation to incorporate unplaced taxa. Abiotic factors potentially driving spatial phylogenetic patterns were tested. Results The distribution of phylogenetic diversity in Iberian angiosperms shows higher values in the Eurosiberian than in the Mediterranean floristic region. CANAPE revealed centers of endemism in mountain ranges (particularly the Baetic System, the Pyrenees, and the Cantabrian Mountains), the Balearic Islands, the semi-arid southeast of the Iberian Peninsula, and some coastal areas. Centers dominated by neoendemism are concentrated in areas combining recent geographic isolation, mediterranean-type climate, and diverse edaphically stressful substrates (calcareous, dolomitic, ultramafic, gypsic), whereas centers dominated by paleoendemism are more scattered and occur under a wider range of abiotic conditions. Superendemism centers occur in the highest mountain ranges (Sierra Nevada and the Pyrenees), the Balearic Islands, and the semi-arid southeast, functioning both as centers of recent speciation and as refugia for phylogenetically isolated lineages. Phylogenetic imputation proved useful in uncovering biologically meaningful spatial phylogenetic patterns that would otherwise remain undetected. Conclusions The Iberian Peninsula is a globally relevant center of endemism. Geographic patterns of phylogenetic diversity and endemism reveal evolutionary and biogeographic processes shaping plant assemblages in the western Mediterranean biodiversity hotspot, while providing a robust framework for informing future conservation strategies.