Tracing the origins of Mediterranean steppe flora: phylogenetics and biogeography of Iberian Astragalus sect. Platyglottis

Abstract The steppe flora of the Mediterranean basin is essential for understanding plant assemblages in the region and is a key target for conservation efforts. Recent phylogenetic and biogeographic studies trace the origins of these lineages to events such as the Messinian Salinity Crisis and Quaternary climatic shifts, but further research is needed to fully understand their evolutionary history. Astragalus sect. Platyglottis Bunge (Fabaceae) includes c. 14 species and subspecies from steppe and semi-arid environments throughout West Asia and the Mediterranean Region. The Iberian Peninsula harbours four members of the section distributed in disjunct and restricted ranges: A. devesae , A. gines-lopezii , A. nitidiflorus and A. peregrinus subsp. warionis . The first three are threatened Iberian endemics. We sequenced the nuclear ITS and the plastid trn K/ mat K region to determine their phylogenetic placement. We also estimated divergence times and ancestral ranges, and analysed plastid DNA haplotypes to further investigate the evolution and genetic diversity of Iberian populations. We found that Astragalus sect. Platyglottis is polyphyletic, but all Iberian taxa form a monophyletic group with two other Mediterranean taxa ( A. peregrinus subsp. peregrinus and A. suberosus subsp. haarbachii ). Ancestral colonisation of the Mediterranean Region from West Asia appears to have occurred since the Pliocene, followed by Pleistocene diversification of the westernmost lineages of Platyglottis . Each Iberian taxon displayed a unique plastid haplotype, shared by all individuals. This study deepens our understanding of some distinctive and threatened Iberian representatives of the largest genus of angiosperms and provides new information regarding their evolutionary history, biogeography and conservation.