Evolutionary distinctiveness with incomplete isolation of the narrow endemic alpine plant Saxifraga delphinensis Ravaud

The growing evidence for the role of introgression in evolution is challenging for species delimitation, taxonomy, and conservation. Here, we examine the isolation of Saxifraga delphinensis, a south-west alpine narrow endemic, from its sympatric congeners Saxifraga exarata and Saxifraga moschata. Our analyses, based on morphological, molecular and genome-wide data, were extended to taxa from Jura, Massif Central, north-east Iberian mountains and Pyrenees to broaden the phylogenetic scope of the study. Phylogenetic results support the close relationship between (i) S. delphinensis, Saxifraga cebennensis and one population of S. exarata from Queyras and (ii) between S. lamottei, S. giziana and S. moschata. Saxifraga exarata, which was extensively sampled, is composed of several clades and is paraphyletic to other taxa. While morphological and genetic data support the evolutionary distinctiveness of S. delphinensis, introgression with S. exarata is shown by various data and analyses. In addition, ABBA-BABA analyses and plastome phylogeny reveal a possible contribution of the north-east Iberian endemic Saxifraga vayredana into the history of S. delphinensis. Overall, the results show a complex evolutionary history with frequent hybridization and spanning several mountain ranges in Europe.