Phylogeography of a west-Beringian endemic plant: An ancient seed of Stellaria jacutica Schischk. detected in permafrost deposits of the last interglacial

Abstract

Beringia, the landmass connecting Eurasia and North America during Pleistocene sea level low stands, played a crucial part in the phylogeographic history of northern plants, animals and humans. Beringia was not only route for migration between both continents but, as the only unglaciated sector of the Arctic, it was also an important refugial area for northern biota during the Pleistocene. The finding of a fossil seed of Stellaria jacutica Schischk., endemic in Yakutia and the Russian Far Eastern Magadan Oblast, in permafrost deposits near Batagay demonstrates the existence of that species in the Yakutian Yana Highlands already during the last Pleistocene interglacial, about 125 ka ago. The biogeographical, ecological and seed morphological characters of S. jacutica allow for conclusions on its phylogenetic relationships. Stellaria jacutica is the only large seeded Stellaria species occurring in northeast Siberia today. According to carpological characters, S. jacutica is closely related to south Siberian large-seeded Stellaria species, which have a centre of diversity in the Altai-Sayan mountain range. This kinship is also suggested by corresponding ecological preferences and occurrence in mountain steppes and rock steppe communities mainly in the alpine belt of mountains. The spread of S. jacutica's ancestor north-eastwards assumedly happened during a Pleistocene cold stage, when the climate in Siberia was cooler, drier and more continental than during warm stages. Spread and following allopatric speciation hence occurred prior to the last interglacial, i.e. during or prior to the middle Pleistocene.