Myrtales: Molecules, Mangroves and Metrosideros

The Myrtales is an ideal group of plants to investigate numerous questions pertaining to molecular systematics and biogeography. The order is one of the most studied and taxonomically stable. However, several key phylogenetic relationships remain unresolved. The current study represents the most comprehensive phylogenetic analysis of the Myrtales utilizing molecular data from each plant genome at various hierarchical levels. Phylogenies are used to examine relationships, test biogeographic hypotheses, and provide age estimates for major lineages to explore the influence of vicariance, dispersal and extinction. Based on our three-genome data set, the Myrtales is monophyletic and originated in Gondwana 120--115 Ma. Nine well-supported clades correspond to the nine accepted families in the order with Combretaceae at the base. To investigate relationships and distributional patterns within Combretaceae, we utilized five cpDNA regions and one low-copy nuclear gene (phyC). Results support a Gonwanan origin for during the Cretaceous (110--102 Ma) with a complex biogeographical history involving both vicariance and dispersal. To explore the modern paradigm of biogeography that invokes vicariance with little attention paid to dispersal biology, we investigated the genus Metrosideros (Myrtaceae) across its South Pacific distribution and utilized molecular data and fossil evidence to time the spread of the genus across the Pacific and estimate its arrival in the Hawaiian Islands---an area where dispersal is the main contributor. Using 13 plastid and 2 nrDNA regions, we find strong support for the monophyly of tribe Metrosidereae, subgenus Metrosideros and the Hawaiian taxa. Divergence time estimates suggest an origin of the tribe 27 Ma with movement to Hawaii occurring ca. 3 Ma. Evidence for dispersal back to the Marquesas Islands corroborates previous findings. We also present the first suggestion of a relationship between South American Tepualia and South African Metrosideros angustifolia within subgenus Mearnsia.