Utility of rDNA ITS sequences in the systematics of Teucrium section Polium (Lamiaceae)

A phylogenetic study based on sequence data from the complete internal tran scribed spacer region (ITS) of nuclear ribosomal DNA for sect. Polium of th e genus Teucrium shows both intersectional congruence and intrasectional in congruence with traditional morphological classifications. We attribute thi s incongruence largely to problems related to the polyploid complex studied . Section Polium includes many poorly differentiated taxa of probable recen t origin through hybridization followed by polyploidization. Both on the ba sis of parsimony and distance (Neighbor-Joining method) analyses, T. dunens e and T. thymifolium are the species that diverge most from the sampled tax a. However, unlike T. thymifolium, the morphology of ir: dunense is not muc h differentiated in relation to the other taxa. Both species are, nonethele ss, the only sampled species to occupy isolated, exclusive environments and which may have undergone rapid evolution by a bottleneck effect. Teucrium dunense is found only on dunes along the Spanish and French coasts and ir: thymifolium, a chasmophytic species with limited endemism, is found solely on limestone and dolomite cliffs in the low mountains in south-eastern Spai n. A hypothesis is presented to explain the discrepancy between the observe d comparatively large amount of ITS sequence divergence and the low morphol ogical differentiation in T. dunense.