The Linaria amethystea complex: convergence, divergence and radiation in the western Mediterranean

The Mediterranean Region is one of the world’s major hotspots of floristic diversity, characterized by a high number of endemic taxa. An example is Linaria amethystea (Vent.) Hoffmanns. & Link (Antirrhineae, Plantaginaceae), a species endemic to the western Mediterranean Region, including the Iberian Peninsula and northwestern Africa, in which a wide morphological diversity has been recognized. This variability has complicated its taxonomic classification, leading to the current recognition of seven subspecies, as well as two recently described, morphologically similar species (L. pseudamethystea and L. semialata). In this study, a phylogenetic analysis of this taxonomic complex was conducted to determine whether the current classification is supported by phylogenetic relationships and investigate its main evolutionary patterns. Phylogenetic trees were reconstructed using plastid (rpl32-trnL, trnS-trnG and trnL-trnF) and nuclear (ITS) DNA regions, complemented by a plastid haplotype network and phylogenetic dating based on plastid DNA sequences. The results indicated that L. pseudamethystea is phylogenetically distant from the rest of the group, suggesting that its morphological resemblance to L. amethystea is the result of evolutionary convergence. Furthermore, the grouping of the northwestern African taxon L. amethystea subsp. broussonetii with L. munbyana indicates that L. amethystea may not form a monophyletic group. Although phylogenetic resolution for the remainder of the complex was limited, results point towards a recent Quaternary radiation of a clade comprising the Iberian subspecies of L. amethystea and other closely related taxa, resulting in a considerable morphological and ecological diversity despite limited genetic differentiation.