DISSOLUTION OF VIBURNUM SECTION MEGALOTINUS (ADOXACEAE) OF SOUTHEAST ASIA AND ITS IMPLICATIONS FOR MORPHOLOGICAL EVOLUTION AND BIOGEOGRAPHY

This study marks a significant increase in the number of species and genetic loci used in reconstructing the phylogeny of Viburnum. In particular, we expanded sampling of the morphologically heterogeneous section Megalotinus of Southeast Asia, which to date has been represented by only one species. Our results provide increased support for the monophyly of most of the previously named clades and for relationships within them. However, the four subsections of Megalotinus are placed with confidence in widely separate places in the phylogeny, and their disparate relationships are supported by morphological characters including branching patterns, inflorescence types, and trichomes. These findings, along with the phylogenetic placement of several additional Southeast Asian species, are critical in assessing the ancestral condition of Viburnum inflorescence architecture and endocarp shape. Our results also highlight a new biogeographic possibility, namely that Viburnum may have originated and initially diversified in montane subtropical forests in Southeast Asia and later moved into northern temperate forests, which most of them are associated with today. This study provides a clear-cut example of the importance of including in phylogenetic studies rare and difficult-to-obtain species from outside the main centers of diversity and of the value of dismantling nonmonophyletic taxonomic groups.