Molecular and morphological investigations on plagiomnium T.J.Kop.taxa distributed in the eastern black sea

The genus Plagiomnium (Bryophyta: Mniaceae) is represented by seven species (P. affine, P. cuspidatum, P. elatum, P. medium, P. ellipticum, P. rostratum and P. undulatum) in the Northeastern Black Sea Region of Türkiye. In this study, morphological and molecular characterization of these species was made and their phylogenetic relationships were revealed. Multivariate statistical analyses of leaf characters (PCA and Hierarchical Clustering) were used within the scope of morphological studies. For molecular phylogeny, the nuclear ITS2 and chloroplast trnL-F regions were sequenced, and phylogenetic analyses were performed using Maximum Parsimony (MP), Maximum Likelihood (ML), and Bayesian Inference (BI) methods. The results, based on the largely congruent morphological and molecular evidence, revealed that P. medium and P. ellipticum are sister species. P. rostratum exhibited transitional characteristics between groups within the genus, whereas P. undulatum and P. cuspidatum were placed in basal positions. The low genetic distance between P. medium and P. ellipticum suggests that evolutionary mechanisms such as past hybridization or allopolyploidy may have played a role between these species. This study highlights the critical importance of integrating morphological and molecular data in resolving the taxonomic problems within the genus Plagiomnium.