Geographical diversification of the genus Cicer (Leguminosae: Papilionoideae) inferred from molecular phylogenetic analyses of chloroplast and nuclear DNA sequences

Cicer L. (Leguminosae: Papilionoideae) consists of 42 species of herbaceous or semi-shrubby annuals and perennials distributed throughout the temperate zones of the Northern Hemisphere. The origin and geographical relationships of the genus are poorly understood. We studied the geographical diversification and phylogenetic relationships of Cicer using DNA sequence data sampled from two plastid regions, trnK/matK and trnS-trnG, and two nuclear regions, the internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of nuclear ribosomal DNA, from 30 species. The results from the phylogenetic analyses of combined nuclear and chloroplast sequence data revealed four well-supported geographical groups: a Middle Eastern group, a West-Central Asian group, an Aegean-Mediterranean group, and an African group. Age estimates for Cicer based on methods that do not assume a molecular clock (for example, penalized likelihood) demonstrate that the genus has a Mediterranean origin with considerable diversification in the Miocene/Pliocene epochs. Geological events, such as mountain orogenesis and environmental changes, are major factors for the dispersal of Cicer species. The early divergence of African species and their geographically distinct region in the genus suggest a broader distribution pattern of the genus in the past than at present.