Phylogenetic Analysis of the Far Eastern Salix (Salicaceae) Based on Sequence Data from Chloroplast DNA Regions and ITS of Nuclear Ribosomal DNA

Abstract

In order to further elucidate the relationships in the Salix genus, phylogenetic ana lysis was conducted based on comparison of the nucleotide sequences of the chlo roplast DNA regions (petG–trnP, petN–psbM, psaA–ycf3, psbM–trnD, rpoB– trnC, trnC–petN, trnD–trnT, trnS–psbZ, rbcL, matK) and the ITS region (ITS1–5.8S rRNA–ITS2) of nuclear ribosomal DNA of 86 Salix species from three sub­ genera: Salix, Chamaetia, Vetrix, 27 sections and Chosenia arbutifolia. The previous ly recognized genera Chosenia and Toisusu merged with Salix. The divergence of spe­ cies in the Salix genus (according to ITS and cpDNA data) was very low. In most spe cies from Chamaetia and Vetrix subgenera, the sequences differed by several sub­stitutions­or­were­ identical.­Molecular­differences­were­ identified­mainly­ in­ spe cies belonging to the subgenus Salix in its previous broad meaning. ITS­phy­ lo­geny­generally­agrees­with­the­most-recent­infrageneric­classification­of ­Salix: the isolation of subgenera Pleuradenia, Chosenia, Salix (for exception sect. Triand­ rae), Longifoliae has been well supported, but the isolation of subgenera Protitea and Chamaetia is not supported. Relationships between the subgenera Chamaetia and Vetrix remain unresolved. High similarity of the plastid and nuclear genomes re vealed in the majority of Salix species included in the analysis may indicate that they have relatively recently diverged from a common ancestor or there is a result of lineage sorting through hybridization. K e y w o r d s chloroplast DNA, ITS, phylogenetic analysis, Salicaceae, Salix