Forest ecotypes of Veronica spicata

The Eurasian steppe area has been a dynamic vegetation type during the Pleistocene with its repeated cycles of forest advances and retreats. Such a scenario allows the evolution of ecotypes at the ecotone with the potential for parallel evolution in different parts of the distribution area. We test this hypothesis using the forest steppe/steppe herb Veronica spicata, based on results from genotyping-by-sequencing and pollen morphology. We provide evidence that the forest-living paczoskiana-morphotype evolved independently in Ukraine (the type locality in central Ukraine) and the Altay region, but potentially also elsewhere. Pollen morphology of 26 herbarium specimens was studied using both light microscopy and scanning electron microscopy. Pollen grains are 3(4)-colpate and 3-colporate, suboblate to prolate (P/E = 0.82–1.75) in shape; small- and medium-sized. Pollen grains of forest ecotypes were usually smaller in size (mean 20.74 × 18.72 µm) than pollen of grassland V. spicata (mean 23.79 × 20.98 µm). Lack of an indumentum, reddish stem color and smaller pollen seem to be parallel adaptations to the shadier and more acidic soil in these forests. The dynamic history of the forest-steppe zone in Eurasia during the Pleistocene provides a compelling scenario supporting the convergent evolution of this morphotype