Genotyping-by-sequencing elucidates the species limits of Ukrainian taxa within Veronica subg. Pseudolysimachium

The subgenus Veronica subg. Pseudolysimachium contains mostly species occurring in natural and seminatural grasslands throughout Eurasia and is characterized by one of the highest diversification rates within Veronica, making it difficult to outline species boundaries, especially in taxa from its diversity hotspots. To resolve species limits among its Ukrainian members, the European diversity hotspot of the group, we combine evidence from GBS, niche modeling, palynology and morphometrics and compare the climatic niches of three closely related species. We confirm that Veronica maeotica and V.steppacea are distinct species. Both taxa, even though previously largely ignored, represent independent lineages in the phylogeny and are characterized each by a unique combination of morphological traits. Veronica steppacea is adapted to a drier, more continental climate than its closest relative, V.barrelieri, highlighting the importance of the zonality of the Eurasian steppe belt in shaping the diversity of the subgenus. Veronicaincana is split into two geographically distinct clades, providing evidence that plants with a cobwebby indumentum arose twice within the subgenus. Two other Ukrainian taxa, V.gryniana and V.incana subsp.hololeuca, may be of hybrid origin.