Genetic diversity and specific delimitation of the Centaurea alba complex in the Iberian Peninsula

Abstract

The high morphological variability of the Centaurea alba complex in the Iberian Peninsula has promoted changes in the taxonomic rank of some species and the description of infraespecific taxa (subspecies and varietes). In our study, we followed the taxonomic treatment based on morphology proposed by López & Devesa (2011). We have investigated genetic diversity and structure of twelve populations comprising nine taxa, and whether the current taxonomic treatment is supported by the molecular data. Microsatellites (6 loci) were used to assess genetic diversity and structure, to identify genetic barriers and to estimate recent gene flow. Most of the studied populations showed values of genetic variability similar to other Centaurea species of subsect. Phalolepis, to which C. alba complex belong. Individuals within all the populations were more related than we would expect, which is attibutable to inbreeding. There was a significant pattern of isolation by distance, although in some cases recent gene flow was found. Patterns of genetic structure gave support to the recognition of C. alba and C. costae, but not to the infraspecific taxa, especially to all the varieties subordinated to both species. For the subspecies C. alba subsp. alba, subsp. aristifera and subsp. tartesiana, introgression with other co-occurring species from subsect. Centaurea, such as C. paniculata sensu lato, has been hypothesized. The three subspecies are recognizable morphologically, but they are weakly supported by molecular evidences.