| Summary: | Fossil evidence suggests that liverworts may have existed already in the Ordovician. The long-standing hypothesis, that widely disjunct geographic ranges of various extant liverwort groups have been largely resulted from vicariance events from fragmentation of widespread ancestors through tectonic plate movements, has been challenged by the recent studies based on molecular data. In this thesis, two groups of the leafy liverworts in the order Jungermanniales were investigated in order to better understand the phylogenetic relationship and biogeography of liverworts. They are the family Schistochilaceae ranging mostly in the Southern Hemisphere, and the cosmopolitan genus Herbertus of family Herbertaceae. Both families possess a diverse morphology and wide disjunct distribution. The phylogeny and biogeographic history of Schistochilaceae and Herbertus were studied by using DNA sequence data of chloroplast and nuclear gene regions. Morphological characters used for species delimitation were also studied and re-evaluated. Schistochilaceae is resolved as monophyletic being one of the early derived leafy liverwort groups. The phylogenetic position of the Chilean endemic Pleurocladopsis simulans is resolved within the genus Schistochila and the new combination Schistochila simulans (C. Massal.) Xiao L. He & Yu Sun is made. Schistochilaceae is inferred to have originated in the Late Cretaceous at c.100 Mya, in an ancestral area including southern South America, West Antarctica and New Zealand. New Zealand was recognized as the early divergence and dispersal center, most dispersals were transoceanic. Herbertus is resolved as a monophyletic group with one clade consisting of the southern hemispheric taxa Herbertus runcinatus, H. oldfieldianus, and H. juniperoideus, and the other including species of H. sendtneri complex and of H. aduncus complex, mostly belonging to the Northern Hemisphere. H. armitanus and H. circinatus were synonymized with H. sendtneri. H. borealis, H. buchii, H. delavayi, H. dicranus, H. kurzii, ...
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