An integrative approach underlines the genomic and morphological divergence of Alpine and Apennine populations of Astragalus onobrychis (Fabaceae), supporting the description of two new species

Recent studies of widespread Eurasian steppe biota have uncovered previously unexpected genetic divergence between populations from edaphic, extrazonal European steppes and their relatives thriving in the vast, zonal steppe belt. For instance, different genetic lineages – partly corresponding to differences in ploidy – were previously identified in Astragalus onobrychis L. (Fabaceae), but the sampling for morphometric analyses was insufficient for taxonomic conclusions. Hence, we strongly increased the sampling effort for both morphometric and genomic analyses to investigate evolutionary origin and differentiation of Alpine and Apennine populations of A. onobrychis using an integrative approach. Our study combined analyses of restriction site associated DNA sequencing, relative genome size estimation, and multivariate morphometric analyses. After establishing the genetic and morphological divergence of the aforementioned populations, we described them as two new species, Astragalus vallium-aridarum E. Huber, Maylandt & Schönsw., sp. nov. endemic to the Alps and Astragalus italicus E. Huber, Maylandt & Schönsw., sp. nov. endemic to the southeastern Alps and the Northern and Central Apennines. We demonstrate that A. vallium-aridarum is a hybrid species originating from cross-ploidy hybridisation between octoploid A. onobrychis and tetraploid A. italicus . We provide diagnoses, descriptions, geographical distributions, and conservation status of these enigmatic elements of extrazonal steppes along with a determination key for the Alpine, Apennine and Pannonian species of the A. onobrychis species group.