Viburnum Phylogeny Based on Chloroplast trnK Intron and Nuclear Ribosomal ITS DNA Sequences

Abstract

Phylogenetic analyses of chloroplast trnK intron and nuclear ribosomal ITS DNA sequences yield signie cant improvements in our understanding of relationships, character evolution, and biogeography in Viburnum (Adoxaceae). We cone rm that most of the ten traditionally recognized sections are monophyletic. The most striking exception is Odontotinus , which is divided into: (i) a purple-fruited New World clade within which the Latin American section Oreinotinus is nested, and (ii) an Old World, mostly red-fruited clade that is closely related to V. cylindricum (section Megalotinus ) and the New World, purple-fruited V. acerifolium . We identify three major supra-sectional groupings: (i) a clade consisting of the Odonto- tinus-Oreinotinus -Megalotinus complex,the circum-boreal section Opulus, andtheEurasiansection Tinus,(ii)acladecontaining the Old World section Viburnum, the New World section Lentago, and, with less support, section Pseudotinus , and (iii) aclade containing the Asian sections Tomentosa and Solenotinus . Two species are not clearly allied to any of these supra-sectional clades: V. urceolatum , a Taiwanese/Japanese species traditionally placed in section Viburnum, and V. clemensiae , a Bornean species previously assigned to section Solenotinus . The placement of the root also remains uncertain, but probably does not fall within any of the three major supra-sectional clades. Knowledge of relationships within sections is useful in clarifying historical biogeography and the evolution of sterile e owers and fruit color. The one case of cone ict between datasets high- lights a possible instance of homoploid hybrid speciation.