Phylogenetics and historical biogeography of Lomaridium (Blechnaceae: Polypodiopsida)

Abstract

Blechnaceae is a worldwide family of leptosporangiate ferns composed of about 250 species. Most of the species in the family were recognised under a single large genus Blechnum until recently, when a new classification proposed the recognition of 24 genera. Given this new systematics of Blechnaceae, which largely resolves the genus-level relationships in the family, there is a need for phylogenetic research to investigate relationships within the majority of the newly proposed genera. In this paper, we unravel the phylogenetic relationships and the historical biogeography of the species of Lomaridium, a genus including most of the hemiepiphytic species in the Blechnaceae. Our sampling includes 11 species, which represents 85% of the diversity in the genus and which covers the entire geographic distribution of the group. We constructed two datasets with three plastid markers: one for phylogenetic analyses (maximum likelihood, Bayesian inference) with four outgroups from phylogenetically close genera (Brainea, Lomaria, Sadleria, Woodwardi); and a second for molecular dating and historical biogeographic analyses that included a larger set of outgroups so that we could accurately reconstruct ancestral events at the base of Lomaridium, under different models. We are able to recognize four highly supported lineages: L. contiguum and the L. schottii, L. attenuatum, and L. fragile clades. Our results date the origin of Lomaridium at some point during the Paleocene epoch, and the most likely geographic area for its origin is Australia plus tropical Central and South America. Several dispersal events are inferred, all of which are most likely long-distance dispersal events. From Australia, we infer a first dispersal event that brought the ancestor of the extant species L. contiguum to New Caledonia. In Central and South America, Lomaridium continued to diversify and colonized additional areas, including the Caribbean (L. binervatum), some Pacific islands (L. schottii), and Africa and Madagascar. While our goal in the current study was not to estimate the biogeographic or diversification history of all Blechnaceae, our analyses do suggest that the early history of the family was complex biogeographically, with extensive long-distance dispersal events. Lomaridium exemplifies this high dispersal capacity, as a genus with only a modest number of species that have reached far-flung regions of the globe via numerous long-distance dispersal events.