Evolution and biogeography of the woody Hawaiian violets (Viola, Violaceae): Arctic origins, herbaceous ancestry and bird dispersal

Specialists studying the genus Viola have consistently allied the Hawaiian violets comprising section Nosphinium-most of which are subshrubs or treele ts-with putatively primitive subshrubs in certain South American violet gro ups. Hawaiian Violets also possess inflorescences, a floral disposition oth erwise found only in other genera of the Violaceae, thus strengthening the hypothesis of a very ancient origin for the Hawaiian species. A survey of p hylogenetic relationships among infrageneric groups of Viola worldwide usin g nuclear rDNA internal transcribed spacer (ITS) sequences revealed a drama tically different biogeographic origin for the Hawaiian violets: A monophyl etic Hawaiian clade was placed in a close sister relationship with the amph i-Beringian tundra violet, V. langsdorffii s. l., in a highly derived posit ion. This remarkable and unforeseen relationship received strong clade supp ort values across analyses, and monophyly of the Hawaiian lineage was furth er indicated by a unique 26-base-pair deletion in section Nosphinium. The h igh polyploid base chromosome number (n similar or equal to 40) in the Hawa iian violets relates them to Alaskan and eastern Siberian populations in th e polyploid V. langsdorffii complex. More than 50 species of the 260 alloch thonous birds wintering in the Hawaiian Islands are found to breed in the A rctic, occupying habitats in which individual birds might have encountered ancestral V. langsdorffii populations and served as dispersers to the centr al Pacific region. Acquisition of derived morphological traits (e.g., arbor escence and inflorescences), significance of a confirmed Arctic origin for a component of the Hawaiian flora, and the likelihood of other "cryptic" Ar ctic elements in the Hawaiian flora deserving independent molecular phyloge netic corroboration are discussed.