The Evolutionary and Biogeographic Origin and Diversification of the Tropical Monocot Order Zingiberales

Zingiberales are a primarily tropical lineage of monocots. The current pantropical distribution of the order suggests an historical Gondwanan distribution, however the evolutionary history of the group has never been analyzed in a temporal context to test if the order is old enough to attribute its current distribution to vicariance mediated by the break-up of the supercontinent. Based on a phylogeny derived from morphological and molecular characters, we develop a hypothesis for the spatial and temporal evolution of Zingiberales using Dispersal-Vicariance Analysis (DIVA) combined with a local molecular clock technique that enables the simultaneous analysis of multiple gene loci with multiple calibration points. We employ a pairwise relative rates test to assign four rate classes to 24 ingroup and 12 outgroup taxa using evidence from three gene regions (rbcL, atpB, ISS). Five nodes of in group and outgroup taxa were calibrated using fossils and previous monocot-wide age estimates. The results are compared with non-parametric rate smoothing and penalized likelihood estimates of temporal diversification. The divergence of Zingiberales from the remaining commelinid monocots is found to have occurred around 124 million years ago, with major family-level lineages becoming established in the late Cretaceous (80-110 mya) and crown lineages within each family beginning to diversify during the early to mid-Tertiary (29-64 mya). Ancestral Gondwanan vicariance combined with a potential Laurasian distribution and multiple secondary dispersal events within families during the Tertiary can explain the main biogeographic events leading to the current pantropical distribution of this tropical order.