Some features in phylogenies may enable us to point out possible evolutionary processes behind them. The convergent evolution of similar phenotypes in ecologically similar environments, rapid diversifications, and correlations between the habitat shift and the evolution of adapted phenotypes, for example, may suggest natural selection as a cause of speciation. Recently the role of developmental plasticity has taken a central role in discussion about natural selection. It may create novel phenotypes which, if they are favoured by selection, can via genetic accommodation lead to genetic differences between populations. Although plasticity and natural selection as a reason for similarity between the populations may sometimes be difficult to assess, the origin of the morphological similarity can then usually be distinguished with experimental studies. In this project I will apply a phylogenetic approach, comparative methods and greenhouse experiments for studying evolutionary processes behind morphological evolution and speciation in mosses. The project consists of case studies that deal with different evolutionary processes and their effect on morphological differentiation. It will produce important information about evolutionary processes behind morphological evolution and speciation and therefore cast light on central questions in evolutionary biology on the role of natural selection, phenotypic plasticity, hybridization, and biogeography in the speciation.