Where do Sardinian orchids come from: a putative African origin for the insular population of Platanthera bifolia var. kuenkelei?

Because of the complex geoclimatic dynamics of the Mediterranean basin, resulting from a combination of Tertiarygeological processes and Quaternary climatic oscillations, the current species composition of the main continentalislands is a mosaic resulting from relative contribution of vicariance, geodispersal and long-distance dispersal byseed. To help distinguish among the contributions of these different dispersal modes to the orchid species richnesson the island of Sardinia, we investigated the genetic structure and phylogeographic relationship of the onlyPlatanthera bifolia var. kuenkelei population on the island. By using plastid DNA sequence variation, we show thatthis recently discovered population is more closely related to the Tunisian P. bifolia var. kuenkelei than to thegeographically closer P. bifolia populations from peninsular Italy. Results from haplotype network constructionsupport the hypothesis that the current distribution of P. bifolia var. kuenkelei (Sardinia and Tunisia) is most likelyexplained by over-sea dispersal. However, haplotype diversity and mismatch analysis of this unique Sardinianpopulation suggest that, if a long-distance dispersal event did occur, it was not recent. More likely, temporarilyfavourable climatic conditions generated a suitable habitat on the island (also in terms of suitable mycorrhizas andpollinators) and thus a transient opportunity for seedling growth and population establishment of P. bifolia var.kuenkelei from North Africa.