Phylogenetic diversity and genome sizes of Astragalus (Fabaceae) in the Lebanon biogeographical crossroad

The Lebanese mountain range is an important zone of plant species richness and endemism where the genus Astragalus constitutes a principal component of plant biodiversity. Most of endemic Astragalus taxa, living in mountains and arid zones of Mounts Lebanon and anti-Lebanon, are characterized by a cushion, spiny vegetative form, named “tragacanthic”, which is a remarkable example of vegetative convergence evolution. Because of determination difficulties, taxonomic uncertainties, and discrepancy in the number of taxa listed according to authors, new data are hardly needed to improve systematics of Astragalus and to investigate the role of the Lebanese mountain range as refugia of biodiversity. Before this study only two values on the genome size of Astragalus were reported in the literature and no previous molecular studies had been carried out on Astragalus genus in Lebanon. We examined the utility of rDNA ITS molecular markers to distinguish Astragalus species of Lebanese mountain range and the variation range of their genome size. The main results revealed a striking diversity in Lebanese Astragalus species with the emphasis of a huge variation of genome sizes, an important inter-specific chromosome polymorphism and the existence of a high phylogenetic diversity. The strict endemic species of the Lebanese mountains are positioned throughout the phylogeny. These results confirm that the Lebanon and anti-Lebanon mounts constitute a third diversity center for Astragalus and that high altitude areas are important refugia of plant biodiversity despite centuries of exploitation by humans.