Phylogeny of non-monophyletic Teucrium (Lamiaceae: Ajugoideae): Implications for character evolution and taxonomy
Teucrium, with an almost cosmopolitan distribution, comprises about 250 species and is the second-largest genus of subfamily Ajugoideae (Lamiaceae). Phylogenetic studies were conducted using nuclear ribosomal DNA (ITS) and chloroplast (ndhF gene, trnL-F region) DNA sequence data from 101 taxa to estimate phylogenetic relationships among Teucrium and its closest allies. We conclude that: (1) Teucridium, Spartothamnella and Oncinocalyx are nested within Teucrium, thus rendering the latter paraphyletic; (2) previously proposed taxonomic classification systems for Teucrium mostly are not supported by our phylogenetic results; (3) Rubiteucris and Schnabelia appear to be sister to Teucrium. Our results indicate that, among various morphological characters, the calyx shape is diagnostic for different clades within Teucrium. Based on the cladograms derived in this study, the pattern of karyotype evolution suggests that switches in ploidy level are common in at least two groups. Adaptations to drought stress and the regional establishment of Mediterranean climates obviously facilitated speciation and the spread of the genus. Molecular dating analyses indicate diversification of Teucrium at the middle/late Miocene boundary, correlated with Tertiary climatic and tectonic changes.