Polyploidy is a major evolutionary force generating new plant species. Hunt et al. explore the dynamics of allopolyploid speciation in the western Mediterranean rock fern Asplenium majoricum at a site where it occurs sympatrically with its diploid parents and their diploid hybrid. Analysis of genetic diversity in allotetraploid and progenitor populations shows recurrent formation of hybrids and polyploids, but polyploid populations have established successfully only in geographic isolation from diploid parent taxa.
