A case study of intragenomic ITS variation in bryophytes: Assessment of gene flow and role of polyploidy in the origin of European taxa of the Tortula muralis (Musci: Pottiaceae) complex

For the first time in bryophyte studies, we performed comprehensive cloning of the ITS region to reveal intraindividual variation of ITS sequences. We assessed relationships among morphologically defined taxa of the polyploid complex of the moss Tortula muralis. Our results detected a monophyletic T. muralis complex comprising T. muralis subsp. mura­ lis, T. muralis subsp. obtusifolia, T. lingulata, T. israelis, and T. edentula. The single accession of T. edentula was found nested within T. obtusifolia, and biphyletic T. israelis was found to be nested within T. muralis. With the exception of T. lingulata, intragenomic ITS sequence variation was high in the T. muralis complex. Most intraindividual sequences were nevertheless only weakly divergent, suggesting their origin via mutations exceeding the rates of concerted evolution. Markedly divergent sequences found within a single individual most probably resulted from gene flow among distant lineages of the complex. Such pattern of ITS variation challenges the traditional morphology-based taxonomy. No phylogenetic signal was associated with ploidy-level variation, suggesting a polytopic origin of the diploids. Interestingly, the pattern of ITS variation together with morphological evidence indicate the autopolyploid origin of some lineages, which renders the T. muralis complex the first group of mosses in which autopolyploidy is implied by molecular markers.