Molecular phylogeny of Salix L. (Salicaceae) inferred from three chloroplast datasets and its systematic implications

Salix is a taxonomically difficult genus and its generic limits and infrageneric division are still highly controversial. We employed sequences of the chloroplast rbcL gene, trnD-T spacer and atpB-rbcL spacer for phylogenetic analyses of Salix. The results strongly support that Salix. Toisusu and Chosenia form a monophyletic group, confirming the merge of Toisusu and Chosenia with Salix. Within Salix s.l., two major clades are recognizable; one contains species of subgenus Salix (excluding sections Triandrae and Urbanianae), with the New World and the Old World species forming strongly supported clades, respectively; and the other includes sections Triandrae, Urbanianae, Chosenia and all species of subgenera Chamaetia and Vetrix, with the latter two subgenera forming a robustly supported subclade but with low resolution. A new infrageneric classification of Salix is herein proposed. The previously recognized subgenus Salix is split into three subgenera: Salix, Chosenia and Triandrae, and subgenera Chamaetia and Vetrix are combined as subgenus Vetrix.