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

Publication Type:Journal Article
Year of Publication:1999
Authors:E. J Oualidi, Verneau, O., Puech, S., Dubuisson, J. Y.
Journal:Plant Syst Evol
Date Published:Jan
Keywords:Evolution, Internal Transcribed Spacer Region (Its), Labiatae, Lamiaceae, Nuclear Ribosomal Dna, Nucleotide-Sequences, Phylogenetic Analysis, Phylogeny, Polyploid Complex, Populations, Rbcl, Sect. Polium, Teucrium, Transcribed Spacer Sequences, Trees

A phylogenetic study based on sequence data from the complete internal transcribed spacer region (ITS) of nuclear ribosomal DNA for sect. Polium of the genus Teucrium shows both intersectional congruence and intrasectional incongruence with traditional morphological classifications. We attribute this incongruence largely to problems related to the polyploid complex studied. Section Polium includes many poorly differentiated taxa of probable recent origin through hybridization followed by polyploidization. Both on the basis of parsimony and distance (Neighbor-Joining method) analyses, T. dunense and T. thymifolium are the species that diverge most from the sampled taxa. However, unlike T. thymifolium, the morphology of ir: dunense is not much differentiated in relation to the other taxa. Both species are, nonetheless, 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 Spain. A hypothesis is presented to explain the discrepancy between the observed comparatively large amount of ITS sequence divergence and the low morphological differentiation in T. dunense.

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