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As ploidy level and mating system can affect genetic diversity and differentiation, we conducted population genetic analyses of two closely related mosses, Scorpidium cossonii (Schimp.) Hedenäs, and S. revolvens (Sw. ex Anonymo) Rubers which differ in ploidy level and sexual system. We collected 315 specimens in total from five populations of S. cossonii and four populations of S. revolvens in the Swiss Alps. Ploidy level, genetic diversity within populations, and genetic differentiation between populations and species were estimated using nine microsatellite markers. In each S. cossonii sample, each locus bore only one allele, while in S. revolvens, seven out of the nine loci were fixed or nearly fixed for two alleles per locus per individual. These findings are consistent with a gametophytic haploid S. cossonii and allodiploid S. revolvens. The haploid and dioicous S. cossonii was genetically more diverse than the (allo)diploid and monoicous S. revolvens. Differences in genetic diversity between the two species may be explained by different mating systems, different population sizes, and different population histories. Genetic differentiation among populations of S. cossonii was higher than among those of S. revolvens. The low genetic differentiation among populations of the monoicous species was not unexpected, since monoicous species frequently produce sporophytes, long-distance spore dispersal is more likely and leads to low differentiation. [ABSTRACT FROM AUTHOR]

The article provides information on the caducous branchlets in Pterigynandrum filiforme. Pterigynandrum filiforme is considered a pleurocarpous moss that has a circumpolar boreal-montane distribution which grows primarily on rocks and trees. Although caducous branchlets or similar structures are seldom found in pleurocarpous moss, a number of species like Platygyrium repens and Leucodon sciuroides regularly bear caducous branchlets. All of these species and Pterigynandrum filiforme are considered dioecious and are either saxicolous or epiphytic.