The genetic diversity of Asplenium viride (Aspleniaceae) fern colonizing heavy metal-polluted sites

Asplenium viride is a diploid species, belonging to the largest genus of the cosmopolitan fern family Aspleniaceae and occurring on various types of alkaline rocks. It is known to colonize sites with high concentrations of heavy metals, exhibiting changes in frond morphology. A. viride can sometimes form new substrate-dependent ecotypes that can be morphologically and genetically different from parental populations. This study aimed to evaluate the morphological and genetic diversity of A. viride, and test for a potential correlation between variability and heavy metal concentration. Analysis of A. viride specimens from one metalliferous and five non-metalliferous sites showed elevated concentrations of heavy metals in roots of metalliferous plants. The concentrations were higher in roots than in aboveground organs, especially in the case of Cd and Pb, suggesting an excluder strategy for these metals. Both metalliferous and non-metaliferous sites were populated by plants with similar ploidy levels. The overall genetic diversity was low (HT = 0.25) and concentrated between populations (GST = 0.62). The obtained 2C DNA content ranged from 8.67 pg/2C to 8.69 pg/2C. STRUCTURE analysis revealed two groups among the studied populations which did not correlate with heavy metal concentrations and were not significantly supported by AMOVA. This suggests that factors influencing genetic diversity of A. viride are a consequence of intragametophytic selfing caused by patchy habitats and subsequent founder effects, resulting from long-distance colonization by single spores. The species has a potential to colonize heavy metal polluted sites; however, it does not seem to form genetically distinct ecotypes at those sites.