Intricate variation patterns in the diploid-polyploid complex of Alyssum montanum-A. Repens (Brassicaceae) in the Apennine Peninsula: Evidence for long-term persistence and diversification

Abstract

Premise of the study: The Apennine Peninsula, one of the three peninsulas of the European Mediterranean, is an important hotspot of genetic and species diversity, but studies devoted to plant evolution are still very scarce in this region. We studied the diploid-polyploid complex of Alyssum montanum-A. repens, focusing on Apennine and adjacent southwestern Alpine populations from southeastern France, with the aim of examining their taxonomic position and evolutionary patterns. Methods: We employed AFLP markers and cpDNA sequences, along with cytotype determination using flow cytometry, and a multivariate morphometric approach. Key results: The Italian and French populations formed two well-delimited groupings within the studied complex that were, in contrast to previous taxonomic treatments, clearly distinct from A. montanum. Populations from southeastern France represent A. orophilum, a previously described but abandoned species. Those from central and southern Italy correspond to A. diffusum, exhibiting high, geographically structured variation (central Apennines, Gargano, and southern Apennines/Calabria). This pattern coincides with hotspot refugial regions, in congruence with the "refugia-within-refugia" hypothesis, and is reflected here in the recognition of three subspecies within A. diffusum. Conclusions: We provide evidence for the presence of Mediterranean refugia for the studied Alyssum montanum-A. repens complex located in central and southern Italy, which, however, did not contribute to the postglacial colonization of Central Europe. Past extinctions, genetic bottlenecks, and recent expansion were inferred in Central Europe, while long-term accumulation of diversity as well as polyploidization occurred in the Apennines. © 2011 Botanical Society of America.