Phylogeny and biogeography of isophyllous species of Campanula (Campanulaceae) in the Mediterranean area.

Sequence data from the nuclear internal transcribed spacer (ITS) were used to infer phylogenetic relationships within a morphologically, karyologically, and geographically well-defined group of species of Campanula (Campanulaceae), the Isophylla group. Although belonging to the same clade within the highly paraphyletic Campanula, the Rapunculus clade, members of the Isophylla group do not form a monophyletic group but fall into three separate clades: (i) C. elatines and C. elatinoides in the Alps; (ii) C. fragilis s. l. and C. isophylla with an amphi-Tyrrhenian distribution; and (iii) the garganica clade with an amphi-Adriatic distribution, comprised of C. fenestrellata s. l., C. garganica s. l., C. portenschlagiana, C. poscharskyana, and C. reatina. Taxa currently classified as subspecies of C. garganica (garganica, cephallenica, acarnanica) and C. fenestrellata subsp. debarensis are suggested to be best considered separate species. Molecular dating, although hampered by the lack of fossil evidence, agrees with the hypothesis that the diversification within the garganica clade was triggered by the climatic oscillations and corresponding sea-level changes during the late Pliocene and Pleistocene. Dispersal-vicariance analysis suggests that the garganica clade originated east of the Adriatic Sea, from where it reached the Apennine Peninsula.