| Summary: | Dicranum is a large genus essentially found in the Holarctic. More than 90 species are currently accepted and about 30 species are recorded for Europe. Dicranum species grow in a broad range of habitats, forming dense, tomentose tufts or cushions, and are easily recognized in the field by their typical _ Dicranum-look _. However, the taxonomy of this genus is controversial. Many species are difficult to distinguish due to their morphological plasticity. Intergrading forms are often found, leading to frequent confusions and unclear taxonomy. In this thesis, species delimitations of temperate and arctic Dicranum lineages were investigated using molecular phylogenetic reconstructions and barcoding methods. Four potential barcode markers (rps4-trnT, trnL-F, psbA-trnH, nrITS) and two additional chloroplast markers (rps19-rpl2 and rpoB) were sequenced for 90% of the species known in Europe. Molecular data were analysed with maximum parsimony, maximum likelihood and Bayesian inferences for phylogenetic investigations. Furthermore, Bayesian approaches were used for testing automated species delimitation methods (generalised mixed Yule coalescent (GMYC) and Poisson tree processes (PTP)). Morphological characters were re-addressed in the light of the molecular phylogenetic inferences. Finally, gametophytic characters were re-examined and scored for statistical analyses in order to evaluate their relevance for distinguishing closely related species
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