Species limits in Veronica hederifolia and relatives: experimental, morphometric, and phylogenetic approaches in a weedy polyploid complex

Abstract Background Polyploid speciation gains increasingly more attention with the ease of larger scale analyses using flow cytometry. Therefore, the analysis of morphological differences discriminating different cytotypes gains increasing importance. Veronica hederifolia and relatives constitute such a group of species, easily differentiated by ploidy but with controversially discussed morphological differences. Here, we provide a comprehensive analysis of DNA sequence data, ploidy analysis and a morphometric study of herbarium material and a growth chamber experiment with variable light and water conditions to understand species differentiation in this group. Results Our results support the recognition of three species in Central Europe differing in ploidy. Diploid V. triloba can be differentiated not only by ploidy but also by a low pedicel/calyx length ratio (< 1.59). Tetraploid V. sublobata can be differentiated from V . hederifolia not only by a longer pedicel/calyx ratio but more consistently by scattered hairs around the pedicel and shorter hairs on the calyx. Leaf characters are highly influenced by light and, therefore, not diagnostic at the species level. We also report the first triploid plant in the group but such hybrids seem to be rare. Conclusions Based on these characters the three Central European species can be reliably differentiated. However, our data also stress the need to investigate the diversity of the group in the Mediterranean more intensively since here the phylogenetic and morphological variation has not been sufficiently analyzed up to now.