In this paper, we studied the relationships of the only surviving Italian population of Ipomoea imperati (Convolvulaceae), a pantropical sandy coastal species, in Sicily and other populations in the Mediterranean region. Herbarium samples which are representative of extinct populations growing in Campania (Italy) were also investigated together with populations from various Atlantic and Mediterranean localities. Chloroplast DNA microsatellites (cp-SSR) and nuclear ribosomal Internal Transcribed Spacer (ITS) sequences were jointly employed, in order to detect relationships among populations. Our aims were several-fold: (1) to clarify if the species is autochthonous in the Mediterranean basin or a post-Columbian introduction; (2) to investigate phylogeographic patterns in the species and (3) to establish the possible role of dispersal in explaining the patterns observed. Chloroplast microsatellite variation indicates that extinct Italian mainland populations of I. imperati from Campania are not closely related to the extant Sicilian one, as they do not share haplotypes. Chloroplast DNA microsatellite variation is largely between populations, and the within populations component accounts for only approximately 10%. CpDNA data is consistent with a single Mediterranean entry point hypothesis or with the notion that some populations display plesiomorphic variability. ITS data is congruent with the possibility that the presence of I. imperati in the Mediterranean is the result of transatlantic dispersal. The population from Sicily and extinct populations from Campania share an ITS type. A Bayesian analysis employing clock calibration data on an expanded ITS dataset with appropriate outgroups indicates that dates of transoceanic distribution are probably earlier than historical times.
Centaurea L. is one of the most widespread, differentiated, and critical genera of Asteraceae in the Euro-Mediterranean area, with more than 100 currently recognized species inhabiting the region. The controversial C. tenorei group, narrowly endemic to the Peninsula of Sorrento (Campania region, southern Italy), includes three weakly differentiated microspecies: C. tenorei Guss. ex Lacaita, C. montaltensis (Fiori) Peruzzi and C. lacaitae Peruzzi. However, their taxonomic distinctiveness and relationships with close or sympatric species are still unclear. In particular, the existence in several localities of individuals with intermediate morphology suggests inadequate taxonomic assessment within the group or hybridization and introgression with other species. In this study we aimed at defining population structure in this complex. With this objective, we sampled the three currently accepted species from their loci classici (i.e., the localities in which the taxa were originally described) and from other localities throughout the range, including populations of difficult identification occurring where the ranges of different taxa overlap. We employed a panel of SNPs obtained via genotyping-by-sequencing for investigations on genetic structure, admixture and ploidy inference, the latter also compared with chromosome counts. Our results showed that Centaurea tenorei s.l. is consistently tetraploid, contradicting the current taxonomy that was also based on ploidy level. Population structure analyses indicated the presence of four to seven clusters, most of which with clear evidence of admixture. Furthermore, contrarily to what previously supposed, we demonstrated a remarkable contribution of C. deusta, more that of C. cineraria in the genetic make-up of C. tenorei. However, we found a population of C. cineraria outside its ecological range, probably driven by climate change, which could be responsible in the future of further hybridization phenomena.
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