Diversity, genetic structure and evidence of outcrossing in British populations of the rock fern Adiantum capillus-veneris using microsatellites

Microsatellites were isolated and a marker system was developed in the fern Adiantum capillusveneris. Polymorphic markers were then used to study the genetic diversity and structure of populations within the UK and Ireland wh ere this species grows at the northern edge of its range, requiring a speci fic rock habitat and limited to a few scattered populations. Three dinucleo tide loci detected a high level of diversity (23 alleles and 28 multilocus genotypes) across the UK and Ireland, with nearly all variation partitioned among rather than within populations. Of 17 populations represented by mul tiple samples, all except four were monomorphic. Heterozygosity was detecte d in three populations, all within Glamorgan, Wales (UK), showing evidence of outcrossing. We make inferences on the factors determining the observed levels and patterns of genetic variation and the possible evolutionary hist ory of the populations.