First insights on the biogeographical history of Phlegmariurus (Lycopodiaceae), with a focus on Madagascar

Abstract

We explored the biogeographical history of a group of spore-bearing plants focusing on Phlegmariurus (Lycopodiaceae), a genus of lycophytes comprising ca. 250 species. Given its wide distribution in the Southern Hemisphere, Phlegmariurus provides a good model to address questions about the biogeographical processes underlying southern distributions, notably in Madagascar and surrounding islands, also called the Western Indian Ocean (WIO). Our aims were (i) to discuss the systematics of the Malagasy species in the light of molecular phylogenetic results, (ii) to provide the first dating analysis focused on Phlegmariurus and (iii) to understand the relative role of vicariance, dispersal and diversification in the origin of the Malagasy Phlegmariurus species.The phylogenetic relationships were inferred based on three plastid DNA regions (rbcL, trnH-psbA and trnL+trnL-trnF) and on a dataset comprising 93 species, including 16 Malagasy species (80% of the total Malagasy diversity for the genus). Our results highlighted the need to combine Malagasy Huperzia species in Phlegmariurus, as well as the polyphyly of widely distributed species: Phlegmariurus phlegmaria, P. squarrosus and P. verticillatus with the Malagasy species not belonging with the types of P. phlegmaria or P. squarrosus. This led us to propose new circumscriptions of Phlegmariurus species, especially in the WIO.Our dating analysis, relying on fossil calibrations, showed that Phlegmariurus would have originated in the Late Cretaceous and diversified in the Early Eocene. The biogeographical analysis highlighted uncertainties about the biogeographical origins of Phlegmariurus: the genus would have started to diversify in an ancestral range covering at least the Neotropics and Australasia. Hypotheses on the biogeographical history of Phlegmariurus were discussed, especially the roles of long distance dispersal, migration via Antarctica and via the Boreotropics. Six long distance dispersal events over the last 40 Ma would explain the Malagasy species diversity of Phlegmariurus, in combination with an important in situ diversification starting in the Miocene.