A unique A. palustris lineage across the Otranto strait: botanical evidence for a past land-bridge?

Phylogeography allows to reconstructthe history of genealogic lineages at the intra- andinterspecific level. Previous studies on the distributionof minisatellite and microsatellite plastidhaplotypes in populations of the Mediterraneanmarsh orchid Anacamptis palustris revealed thatpopulations from the Salento peninsula (Apuliaregion, west coast of Otranto strait) formed adistinct and isolated lineage. To further explore thepeculiarity of this biogeographic region, in thepresent study we examined both fresh samples andherbarium specimens of the rare orchid Anacamptispalustris from populations located on the easterncoast of the Otranto strait (i.e. on the Greek-Albanian side). All the investigated samplesexhibited a unique combination of chloroplastmicrosatellites, which was previously found exclusivelyin populations from the Salento peninsula.Samples from Corfu, Igoumenitsa and Durazzoshowed a novel minisatellite repeat type, whilethose of Zakynthos possessed the widespreadancestral repeat type. Interestingly, the novel repeattype and those previously found in Salento populationsclustered together on a well-differentiatedevolutionary branch in a minisatellite repeat typenetwork of the A. palustris lineages. This findingindicates a close relationship between the populationsfrom both sides of the Otranto strait andsupports the geological evidence for the occurrence of an ancient land-bridge connection between thesouthern most part of Italy and Greece during theMessinian desiccation and/or the ‘‘Lago-Mare’’period.