Molecular phylogeny and morphological reconstructions of Plagiochilaceae (Jungermanniopsida) with hypotheses on biogeography and divergence times

Abstract

Plagiochilaceae are one of the largest families of leafy liverworts, with an estimated species number of about 500, the magnitude of them placed in the genus Plagiochila. Members of the family occur worldwide from the high north to the far south. Despite the broad geographical amplitude of the family, most of the species occur in the humid tropics.In this work three independent genetic markers from two different genome types (chloroplast rps4 and rbcL, nuclear ITS region) of 120 Plagiochila species as well as 8 species of other genera currently accepted in the same family were sequenced. Complex phylogenetic analyses including up to 7 different evolution models lead to a highly supported 3-marker-topology. The molecular delimitation of the original concept of the Plagiochilaceae has been evaluated based on further plastid rps4 and rbcL sequences from international databases. The aspect of structural conservation and folding patterns of the nuclear ITS region, as known from organisms like yeast, green algae or flowering plants, was adapted and used for modelling of stable secondary structures of the nuclear markers ITS1 and ITS2, therefore providing the first structure model for liverworts of this region.These genetic data were compared to 34 morphological characters, which have been evaluated from literature and were plotted on the 3-marker-topology. Morphological delimitations of 18 sections of Plagiochila and 7 genera of Plagiochilaceae were analysed, including three sections that appear for the first time in molecular studies. The distribution of homoplastic, synapomorphic, and autapomorphic characters was analysed with respect to taxonomic selection of the analysed species, revealing most morphological characters as homoplastic.Biogeographical models have been developed, describing hypothetical origin and dispersal events of the sections of Plagiochila. In an attempt to obtain further insights into the prehistorical world-wide development and distribution of the family, it was tried to calibrate a molecular clock, based on one fossil and two geographical events. Divergence times fit to the results of the biogeographical analyses, but will have to be checked when more fossils are available. Nevertheless, this is the first trial for the molecular dating of a liverwort family. In this study, Australasia is identified as the putative origin of the family, whose development over the last 140 million years leads to the worldwide distribution we can see today.