| Summary: | This project investigates the population genetics of the fern <i>Asplenium hemionitis </i>L. with a view to elucidate its biogeographic history. <i>A. hemionitis</i> is distributed in the Macaronesian region (Azores, Madeira, Canary Islands and Cape Verde) and a few restricted coastal sites on the mainland (W. Portugal and NW Africa). Nuclear (isozymes) and organelle (Chloroplast) markers have been used to investigate 105 populations covering most of the distribution range of <i>A. hemionitis. </i>Population genetic analysis based on isozyme markers show that whereas outcrossing appears to be the prevailing breeding system in populations of <i>A. hemionitis,</i> there is evidence for inbreeding. The amount of inbreeding verified is mostly due to intergametophytic selfing and may be associated with limited spore dispersal and fine structuring within populations. Populations sampled across the Macaronesian islands and the mainland maintain high levels of isozyme diversity, the highest levels being found on the Canary islands and Madeira. This diversity is distributed mainly within rather than between populations. Estimations of differentiation and genetic distance show that Madeira is highly divergent from all the other regions but more from the mainland. The less divergent regions are the Canary Islands and Portugal, and the former and the Azores. The whole population set shows significant isolation by distance and, although less is verified within regions and islands, it is still significant. Sequencing of the <i>trn</i>L and <i>rps</i>4 regions of the chloroplast genome (c.1860 bp) revealed 29 haplotypes and high diversity within all regions. Analysis of differentiation between populations and geographical regions shows that <i>N</i><sub>ST</sub> (takes into account genetic similarities between haplotypes) is higher than <i>G</i><sub>ST</sub> (based on variation in haplotype frequencies alone). This result implies a certain degree of phylogeographic structure, showing that <i>A. hemionitis </i>has been evolving independently within the main archipelagos and the mainland.
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