Several lines of evidence suggest that recent long-distance dispersal may have been important in the evolution of intercontinental distribution ranges of bryophytes. However, the absolute rate of intercontinental migration and its relative role in the development of certain distribution ranges is still poorly understood. To this end, the genetic structure of intercontinental populations of six peatmoss species showing an amphi-Atlantic distribution was investigated using microsatellite markers. Methods relying on the coalescent were applied (IM and MIGRATE) to understand the evolution of this distribution pattern in peatmosses. Intercontinental populations of the six peatmoss species were weakly albeit significantly differentiated (average F(ST) = 0.104). This suggests that the North Atlantic Ocean is acting as a barrier to gene flow even in bryophytes adapted to long-range dispersal. The im analysis suggested a relatively recent split of intercontinental populations dating back to the last two glacial periods (9000-289,000 years ago). In contrast to previous hypotheses, analyses indicated that both ongoing migration and ancestral polymorphism are important in explaining the intercontinental genetic similarity of peatmoss populations, but their relative contribution varies with species. Migration rates were significantly asymmetric towards America suggesting differential extinction of genotypes on the two continents or invasion of the American continent by European lineages. These results indicate that low genetic divergence of amphi-Atlantic populations is a general pattern across numerous flowering plants and bryophytes. However, in bryophytes, ongoing intercontinental gene flow and retained shared ancestral polymorphism must both be considered to explain the genetic similarity of intercontinental populations.

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The distribution of Sphagnum cuspidatum has been subject to controversy. Although historically reported from all continents except Antarctica recent authors consider S. citspidatum to be endemic to Europe and eastern North America. Microsateilites from Australian plants morphologically identified as S. cuspidatum were compared to microsatellites of plants morphologically identified as S. cuspidatum collected from other regions. The species was found to occur in Australia as well as on every continent except Antarctica. The sample most closely related to the Australian plants was collected in the Philippines, and samples from Australia, the Philippines, Colombia, and Equatorial Guinea formed a subclade within S. cuspidatum. Microsatellites further show that S. cuspidatum is one of the parental species of the double allopolyploid S. falcatulum, a Holantarctic species which is reported from Tasmania, New Zealand, and Chile.

Bryophytes seem particularly suitable to investigate genetic diversity in relation to habitat disturbance due to their large employment as bioindicators and to the recent application of molecular markers to moss population studies. Genetic variation and structure were analysed in seven urban, extraurban and remote populations of Leptodon smithii, an epiphytic moss of Quercus ilex, a phanerogamic species of Mediterranean climax vegetation. A total of 210 individual shoots were DNA extracted and amplified with internal simple sequence repeat (ISSR) primers, and 54 haplotypes were identified. An uneven distribution of haplotype number and frequencies was observed among sites, with a higher number of haplotypes and more homogeneous haplotype frequencies in the extraurban/remote populations. Molecular diversity indices were overall higher in the extraurban sites than in the urban ones. Multilocus linkage disequilibrium values were in line with the occurrence of sexual/asexual reproduction in the seven populations. The isolation-by-distance model was not supported by Mantel test among sites; however, within-population fixation index (F(ST)) highlighted a clear relation between genetic and physic distances among trees, suggesting a limited dispersal range for L. smithii's spores. The genetic structure was mainly affected by population size, wood structure and extent, and genetic drift consequent to habitat fragmentation and human-induced disturbance.

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Microsatellite markers were used to test whether two recently described species of Sphagnum (Bryophyta), S. atlanticum R.E. Andrus and S. bergianum R.E. Andrus, represent distinct gene pools. The first species is considered endemic to eastern North America while the second species has been reported from Alaska and Newfoundland. The results indicate that S. atlanticum does not differ genetically from the closely related species, S. torreyanum, also restricted to eastern North America. In fact, some samples that are identical across all 15 microsatellite loci have been distinguished morphologically as these two species. Plants of S. bergianum from Alaska are closely related genetically to Alaskan plants of the similar species, S. subfulvum, whereas Newfoundland plants of S. bergianum are more closely related to Newfoundland plants of S. subfulvum. Alaskan versus Newfoundland plants of S. subfulvum s.l. (including S. bergianum) are differentiated at microsatellite loci. Another closely related species, S. subnitens, is distinct from S. subfulvum and S. bergianum. Sphagnum atlanticum is synonymized under S. torreyanum and S. bergianum is synonymized under S. subfulvum.

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Bryophytes have sometimes ambiguous morphological diagnostic features, so molecular markers can prove a useful tool in systematics, even more in a well known morphologically variable moss such as Hypnum cupressiforme. This paper focuses on genetic diversity in the H. cupressiforme complex inferred by ISSR markers and ITS and trnL sequences. Shoots from nine Italian populations of H. cupressiforme and from five other species included in the complex were analysed. Sequence divergence among the analysed species is very low, with the exception of Hypnum jutlandicum. The neighbour joining tree based on ISSR data shows that all the H. cupressiforme samples do not merge into a distinct cluster, but spread on the whole dendrogram. Molecular variance is partitioned more within-than between-species. Therefore, the genetic variation detected by ISSR at intra-and inter-specific level appears to be, to a large extent, the result of the individual variation, suggesting that the polymorphism detected appears poorly informative at a taxonomic level. Our results suggest that morphological variation of the H. cupressiforme complex does not always correspond to genetic diversity, and highlight a major molecular divergence of H. jutlandicum within the complex.