Viburnum Phylogeny Based on Chloroplast trnK Intron and Nuclear Ribosomal ITS DNA Sequences
Phylogenetic analyses of chloroplast trnK intron and nuclear ribosomal ITS DNA sequences yield significant improvements in our understanding of relationships, character evolution, and biogeography
in Viburnum (Adoxaceae). We confirm 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 Odontotinus-Oreinotinus-Megalotinus complex,
the circum-boreal section Opulus, and the Eurasian section Tinus, (ii)a clade containing the Old World section Viburnum, the New World section Lentago, and, with less support,
section Pseudotinus, and (iii) a clade 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 flowers and fruit color. The one case of conflict between datasets highlights a possible instance of homoploid hybrid speciation.
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