Phylogenetic reconstruction of Asperula sect. Cynanchicae (Rubiaceae) reveals a mosaic of evolutionary histories

摘要

In the present study, we attempt to reconstruct the phylogeny of Asperula sect. Cynanchicae (Rubiaceae: Rubieae), using both nuclear and chloroplast DNA markers. We test different methodological approaches to clarify relationships and to hypothesize divergence times for the section. The inferred phylogenetic hypothesis shows that sect. Cynanchicae is eastern Mediterranean to western Asian in origin and that a clear East/West split occurred early in the diversification of the section. Several species are not sharply separated and, from a morphological point of view, clear synapomorphies are lacking. Informal groups previously described (such as "ser. Palaeomediterraneae") are often artificial. Asperula aristata and A. cynanchica, the two most widespread species of the section, turned out to be non-monophyletic. According to our results, they were probably involved in the origin and/or in the diversification of various extant members of the section. The evolution of A. sect. Cynanchicae has been shaped by a succession of events, among which incorporation of extraneous genomes by genetically aggressive species, progenitor-derivative speciation and hybridization, played a major role.