Biogeographic history of two Eurasian Cenozoic charophyte lineages

Abstract

The long-term biogeographic history of charophytes is a highly relevant, although little-studied topic to understand the distribution of extant species. Two contrasting biogeographic histories of Eurasian charophyte lineages are documented and the reasons for such wide distributions are explored. Nitellopsis (Tectochara) merianii–Nitellopsis obtusa is a charophyte lineage ranging from the latest Eocene to the present and displaying Eurasian distribution since the Late Oligocene. Lychnothamnus stockmansii–Lychnothamnus major lineage is defined here as an Eurasian charophyte lineage ranging from the Late Eocene to the Early Oligocene. Both lineages are well documented in the fossil record owing to their applications in stratigraphic dating. The historical biogeography of these lineages displays two opposite patterns. The lineage L. stockmansii–L. major displays an Eurasian distribution from its first occurrence in the Late Eocene, whilst the lineage N. (T.) merianii–N. obtusa underwent a long period of European provincialism ranging from the Late Eocene to the end of the Early Oligocene (an interval of 10 million years, Ma), to begin later, during the Late Oligocene and Miocene, an eastwards expansion until reaching its present Eurasian distribution. These two different biogeographic patterns appear to be related to the contrasting mechanisms of dispersal in monoecious vs dioecious charophytes, well known in extant Chara, and allow us to identify the time needed by characeans to reach supra-continental distributions.