Metrosideros (Myrtaceae) in Oceania: Origin, evolution and dispersal

Abstract

AbstractMetrosideros (Myrtaceae) comprises 58 woody species distributed across Oceania and with three singleton outliers in Philippines, South America and Africa. Centres of species richness occur in New Zealand and New Caledonia. This distribution accords with a proposed Gondwanan origin for the family. While the phylogeography of one component of the genus – subgenus Metrosideros – has received some examination, the rest of the genus has not been resolved. In this study, we improve resolution of the phylogeny of Metrosideros and consider origin, possible vicariant relationships, long‐distance dispersal events and dispersal routes for the genus. A Bayesian phylogeny, with all but one recently described species of Metrosideros, was constructed using concatenated ITS + ETS rDNA from samples we collected and sequenced. Relative to previous work on Metrosideros using ITS alone, here, using ITS plus ETS, we produce a more detailed and robust phylogeny with a near threefold increase in significant nodal support. Putative centres of origin/diversification, vicariant events and dispersals were considered with reference to the phylogeny, present‐day diversity and fossil record of Metrosideros. Metrosideros occurs as five clades, including the former genera Tepualia and Carpolepis. The paraphyletic and now superseded subgenus Mearnsia included elements of four of these clades, whereas subgenus Metrosideros forms a single clade with robust support. Our phylogeography indicates multiple dispersal/vicariant events within the history of the genus, a number of which involved New Zealand. Among other such events, we infer an exceptional 6300 km trans‐equatorial dispersal from Fiji to the Bonin Islands (Japan). Australia and New Zealand, respectively, are the likely landmasses of origin and diversification for Metrosideros. Typical patterns of floral dispersal proceed from large continental landmasses onto increasingly remote islands and with distance from continent species diversity usually declines. However, Metrosideros shows a countervailing pattern since relatively remote islands are the main centres of speciation and dispersal.