Genetic diversity and origin of the rare, narrow endemic Asperula crassifolia (Rubiaceae)

We examined the patterns of genetic variation in the narrow endemic Asperula crassifolia (Campania, southern Italy), taking into account the schizoendemic distribution of the Mediterranean members of Asperula sect. Cynanchicae. We obtained plastid DNA sequences of the rps16 intron and the trnC-petN intergenic spacer for several members of A. sect. Cynanchicae, for three living populations (48 individuals) and ten herbarium specimens of A. crassifolia. We also analysed nSSR data for A. crassifolia, to infer population diversity and differentiation. Our results suggest that the centre of diversity of A. crassifolia is the island of Capri, where A. crassifolia harbours four different ptDNA haplotypes, two of which are shared with other species of sect. Cynanchicae. Microsatellite analyses revealed low levels of genetic diversity for the mainland population (Nerano, Sorrentine Peninsula) and the neighbouring Sirenusae islets. Diversity in A. crassifolia is mainly explained by ancestral variation and recent divergence. Rarity in A. crassifolia is a natural condition; however, we express concern for the small census population size as it might trigger further rarefaction.