Diversification of fescues (Festuca sect. Eskia, Poaceae), a key‐component of southern European mountainous grasslands

Abstract Grasslands cover approximately 30% of all land area and represent one of the most extensive and diverse ecosystems of the world. One of the largest globally distributed genera dominating various types of grasslands is Festuca (Loliinae, Poaceae). In this study, we disentangle the origin and diversification of early divergent lineages within fine‐leaved (FL) Loliinae, namely F . sect. Eskia and F. sect. Dimorphae (Eskia‐Dimorpha Group). We inferred phylogenetic relationships among 218 populations of 129 Loliinae taxa using nuclear ribosomal ITS and plastid trnT‐trnF sequences. Relative genome size (RGS) and ploidy level estimations revealed multiple polyploidisations within F. sect. Eskia . We uncovered previously unknown tetraploid and hexaploid populations of different species from the Balkan Peninsula. The inferred phylogenies revealed the sequential divergence of Eskia‐Dimorpha Group lineages in the early evolution of FL Loliinae, but also incongruences in the position as well as the composition of different clades between the nuclear and plastid‐based trees. Despite incongruences, some well‐supported and geographically segregated clades of single or closely related species from the Alps, the Pyrenees or the Balkan Peninsula were resolved. The most pronounced discordance between the plastid and nuclear data were among several taxa endemic to the Balkan Peninsula. Our data suggest that genome downsizing followed polyploidisation and that evolutionary dynamics of RGS‐ups and downs within F. sect. Eskia were strongly phylogenetically correlated. Overall, our study underscores the intricate evolutionary history and differentiation of species within the Eskia‐Dimorpha Group, emphasizing the need for further research to refine phylogenetic hypotheses and taxonomic circumscriptions, thereby enhancing our understanding of grassland biodiversity and evolution.