Biogeography of the Gondwanan tree fern family Dicksoniaceae-A tale of vicariance, dispersal and extinction

Aim: Are the disjunct distributions of ancient lineages on continents in the Southern Hemisphere determined by vicariance following the Gondwanan tectonic breakup or recent long-distance dispersal? We traced the historical biogeography of the tree fern family Dicksoniaceae (145 Ma), which has a typical Gondwanan distribution, to test for vicariance or recent long-distance dispersal. Location: Subtropical, tropical and temperate forests of the Southern Hemisphere. Methods: We performed a molecular phylogenetic study of the family based on four chloroplast markers using Bayesian and maximum likelihood inference. Spore fossils served to calibrate the dating of the phylogeny using BEAST. The historical biogeography of the family was traced via an ancestral area reconstruction using a maximum likelihood approach. Results: We corroborated the genus Dicksonia (widespread) as sister to Lophosoria (Neotropical), with Calochlaena (Palaeotropical) as sister to both. The phylogenetic splits between the genera predate the break-up of Gondwana. Lophosoria is currently restricted to America but fossils document extinct populations in Australia, Tasmania and Antarctica. Within Dicksonia, we found three clades which separated 55-25 Ma: one including species from New Caledonia, New Zealand and Fiji; another containing species from the Neotropics as well as southern Australia and New Zealand; and one with species from northern Australia to the Philippines and Sumatra. Vicariance and ancient long-distance dispersal can equally explain the occurrence of these three clades on different tectonic units of Gondwana. Other geographical disjunctions, for example, between Australia and Malesia, are more recent (15-3 Ma) and inferred to be the result of long-distance dispersal. The combination of fossil evidence and island endemics whose ages predate the ages of the islands point to substantial extinction in the genus. Main conclusions: The biogeographical history of the family Dicksoniaceae, and especially of Dicksonia itself, appears to have involved a much more dynamic interplay of vicariance, dispersal and extinction than inferred from current distributions alone. Dicksonia is one of the few biogeographical Gondwanan floristic elements whose current distribution can at least partly be linked to plate tectonic events.