A Phylogeny of Toadflaxes (LinariaMill.) Based on Nuclear Internal Transcribed Spacer Sequences: Systematic and Evolutionary Consequences

Abstract

Premise of research. Toadflaxes (Linaria Mill., ∼150 spp. from the Palearctic region) constitute the largest genus of the snapdragon lineage (tribe Antirrhineae). Here we provide the first extensive phylogenetic testing of systematic and evolutionary hypotheses about toadflaxes. Methodology. Internal transcribed spacer (ITS) sequences were obtained for 94 species representing all sections of Linaria recognized by recent taxonomic treatments, as well as three species of the morphologically related American genus Nuttallanthus. In addition, 71 sequences representing the remaining 26 genera of Antirrhineae were gathered to test the monophyly of toadflaxes. Phylogenetic analyses were conducted using Bayesian inference and maximum likelihood. Evaluation of alternative topologies was assessed by means of Bayes factor analyses. Pivotal results. Linaria and Nuttallanthus constituted a monophyletic group within the Antirrhineae. Linaria was recovered as a paraphyletic group with Nuttallanthus nested within it. Six major clades were recognized within the Linaria-Nuttallanthus clade. The seed wing, a structure that has been extensively used in systematic treatments, appears to be a homoplasious character in Linaria. Conclusions. The circumscription of Nuttallanthus within Linaria is suggested to preserve the monophyly of the latter genus. Three sections of Linaria (Macrocentrum, Pelisserianae, and Versicolores) that are well defined by distinct morphological traits are also supported as natural groups, while monophyly of the remaining sections (Supinae, Linaria, Speciosae, and Diffusae) is unsupported by our results. Habit, inflorescence, and flower morphology, coupled with seed morphology, are revealed as the key characters in the evolution of toadflaxes.