Molecular systematics and biogeography ofWisteriainferred from nucleotide sequences of nuclear and plastid genes

Abstract

AbstractPrevious molecular phylogenetic studies of Fabaceae indicated that species ofWisteria, an intercontinental disjunct genus between eastern Asia and eastern North America, formed a clade derived from withinCallerya. However, interspecific relationships were not well resolved or supported. In this study, we used sequences of the nuclear ribosomal DNA internal transcribed spacer region and the chloroplast genematKto examine interspecific relationships and explore implications of the phylogeny for the systematics and biogeography ofWisteria. Our results showed thatWisteriawith deciduous leaves and racemose inflorescences formed a strongly supported clade derived from within the paraphyleticCallerya.Afgekiawas also found to be included withinCallerya. Therefore, our data support the merger ofAfgekia,Callerya, andWisteria. The phylogenetic pattern suggested that the deciduousness inWisteriamay be a derived trait likely in response to temperate climate, and the racemose inflorescences in theAfgekia–Callerya–Wisteriaclade may have evolved from panicles. Our study also provided strong support for the sister relationship of the North American and eastern Asian species ofWisteria. In the Asian clade,Wisteria brachybotrysSiebold & Zucc. of Japan was sister to the clade containingW.floribunda(Willd.) DC of Japan and Korea, andW.sinensis(Sims) Sweet of China. However, our data offered weak support for the sister relationship ofW. floribundaandW. sinensis. Our divergence time and biogeographic analyses suggested that the eastern Asian–North American disjunction inWisteriamay have occurred through a dispersal event in the middle Miocene (13.4 Mya) from the Old World to the New World across the Bering land bridge followed by vicariance in the late Miocene (6.8 Mya). This study added another example to the “out of Asia” migration for the eastern Asian–eastern North American disjunction.