Phylogeny of Asperula L. sect. Cynanchicae (DC.) Boiss. (Rubiaceae)

The present study is aimed at a phylogenetic reconstruction of Asperula L. sect. Cynanchicae (DC.) Boiss., the richest section for number of taxa belonging to the genus Asperula (tribe Rubieae, family Rubiaceae). Systematic boundaries in the tribe Rubieae are somehow artificial, as several genera resulted to be paraphyletic or even polyphyletic (i.e. Galium, Asperula). However, it is not conceivable to re-arrange generic assemblages without previously understanding and establishing intra-specific circumscriptions. In addition to strictly phylogenetic issues, this work also includes a phylogeographic effort on a single species, the endemic Asperula crassifolia L., which was chosen as a model species to undertake a study focused on population diversity and conservation issues. Different phylogenetic approaches (maximum parsimony, maximum likelihood and Bayesian inference) were employed for reconstructing the evolutionary history of approximately 70 entities of Asperula sect. Cynanchicae, using nuclear ribosomal Internal Transcribed Spacers sequences and two chloroplast spacers (trnC-petN, petN-psbM). Moreover, divergence time within the section were estimated using a Bayesian approach and biological processes (e.g., reticulation, incomplete lineage sorting) subtending phylogenetic relationships were evaluated. Asperula crassifolia was sampled for its entire distribution range (the island of Capri, Sorrentine Peninsula and Sirenusae archipelago) and nuclear simple sequence repeats (SSR) were isolated for the species. Furthermore, rps16 intron variability was investigated in order to formulate phylogeographic hypothesis about the divergence of different populations. Molecular homogeneity of Asperula sect. Cynanchicae resulted extremely evident; divergence time estimation indicates that the section originated during Miocene and terminal nodes are the outcome of geological and climatic vicissitudes occurred during the Tertiary and Quaternary. Probably, reproductive barriers between some taxa of the section are totally lacking, contributing to obscure phylogenetic signal. Hybridization is likely also involved, and this partly prevented the homogenization of the ITS sequences as a consequence of concerted evolution. As far as biogeographical history of A. crassifolia is concerned, the maximum number of haplotypes is recorded for Capri; therefore the origin of the species appears more plausibly to have occurred in this island. Nevertheless, the sympatric presence of A. aristata subsp. aristata does not allow to exclude crossing between the two entities. The rarity of A. crassifolia gives strong indications for safeguard by law.