Molecular phylogeny of the genera Digitalis L. and Isoplexis (Lindley) Loudon (Veronicaceae) based on ITS- and trnL-F sequences

To investigate phylogenetic and biogeographic relationships all species of Digitalis and Isoplexis and one species of the outgroup genera Antirrhinum and Globularia each were analyzed using nuclear ITS and plastid trnL-F sequences. Phylogenetic trees resulting from separate analyses were highly congruent. Combined analysis revealed two major lineages, which mark an early split in the genus Digitalis. While sections Digitalis, Frutescentes and Globiflorae appear monophyletic, sect. Tubiflorae is polyphyletic and sect. Macranthae should be expanded due to paraphyly. Our results provide evidence that all species of the genus Isoplexis have a common origin and are embedded in Digitalis. Isoplexis therefore should be reduced to sectional rank. The phylogenetic placement combined with ecomorphological characters indicates that Isoplexis may be a bird-pollinated Tertiary relict. Results are discussed in the context of biogeography, chemotaxonomy and morphology.