Molecular and fossil evidence disentangle the biogeographical history of Podocarpus, a key genus in plant geography

Abstract

Aim The genus Podocarpus (Podocarpaceae) provides an opportunity to contrast biogeographical hypotheses within and among continents, and to analyse divergence between disjunct tropical and temperate forests of South America. We developed a calibrated phylogeny of Podocarpus to reconstruct the ancestral areas and potential expansion routes within Podocarpaceae. Location Podocarpus consists of two extant subgenera: Foliolatus from Asia and Oceania, and Podocarpus located in Gondwanan continents and north to the Caribbean. The paper focuses mainly on the area occupied by the latter subgenus. Methods We combined previously published and novel DNA sequences with fossil records. New species sequenced are members of Podocarpus subgenus Podocarpus from South and Central America. We assembled DNA sequences of the chloroplast (matK and rbcL) and nuclear (ITS1 and ITS2) to analyse phylogenetic relationships within Podocarpus subgenus Podocarpus by Bayesian methods, which were calibrated using macrofossils that could be confidently identified as modern genera. Ancestral areas were inferred using the dispersal–extinction–cladogenesis model. Results The phylogenetic reconstruction inferred a minimum age for the origin of Podocarpus s.l. in the late Cretaceous–early Palaeogene (63 Ma) and strongly supported monophyly of the genus Podocarpus and of subgenera Podocarpus and Foliolatus. Subgenus Podocarpus consists of two monophyletic, latitudinally structured clades. One clade consists of temperate American species while the other includes species from tropical-subtropical Africa and South America. Main conclusions The history of the subgenera within Podocarpus is older than previously reported: they can be traced back to late Cretaceous–early Palaeocene biogeographical connections between Australasia and South America through Antarctica. Latitudinally disjunct lineages within South America most probably diverged from widespread ancestors as a result of a persistent arid barrier that was established prior to the late Palaeogene. The calibrated age for the Tropical–Subtropical clade suggests an Atlantic–subtropical biogeographical corridor between South America and Africa long after the breakup of Gondwana and the stabilization of the circum-Antarctic current.