Exploring the intricate evolutionary history of the diploid–polyploid complex V eronica subsection P entasepalae ( P lantaginaceae)

V eronica subsection P entasepalae is a diploid–polyploid complex of c . 20 species distributed in E urasia and N orth A frica, in which species boundaries are difficult to determine. Here, we present the first comprehensive phylogenetic analysis of V . subsection P entasepalae based on nucleotide sequences [internal transcribed spacer ( ITS) and the plastid trnH‐psbA and ycf6‐psbM spacers] combined with ploidy estimations. Our results support the monophyly of the subsection. Five well‐supported clades are recovered in the ITS sequence analyses, corresponding to broad geographical areas. The causes of the extensive incongruence found between the ITS and plastid DNA datasets, namely incomplete lineage sorting and/or hybridization and polyploidization, are discussed. Most of the diploids traditionally recognized based on morphological characters and one tetraploid are each recovered as monophyletic by the ITS sequence analyses. The Balkan species V . kindlii is resurrected. DNA ploidy level for V . teucrioides is reported here for the first time (2 x ). Diploid populations have been found for V . orbiculata , which was previously thought to be only tetraploid. Past contact in the amphi‐ A driatic area between V . orsiniana and V . orbiculata is suggested. Finally, molecular analyses show that diploid V . jacquinii and diploid V . orbiculata are unrelated. This study contributes to our understanding of the evolutionary history of polyploid complexes, especially those in southern E urope, and highlights the importance of using multiple lines of evidence to investigate species boundaries in such actively diversifying groups. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 179 , 670–692.