Bupleurum L. (Apiaceae: Apioideae) is a genus of ca. 150 species with broad distribution in the N Hemisphere (except the S African B. mundii), but with many species that are rare or restricted to small areas. The genus is easily recognized within the family because of its simple and entire leaves, but unusually includes woody members as well as the more usual annual and perennials herbs. Bupleurum has for long been regarded as a natural group but its infrageneric classification has been problematic. Phylogenetic relationships of the genus were investigated using sequences of the internal transcribed spacers (ITS) of nuclear ribosomal DNA, from 32 species (35 taxa) representing all sections and subsections of the genus. Phylogenies generated by maximum parsimony, maximum likelihood, and neighbour joining methods show very similar topologies, unequivocally demonstrating monophyly of Bupleurum and the division of the genus into two major clades (100% bootstrap support in all analyses). The most basal clade is formed by all the species of the genus with pinnate-reticulate veined leaves, and surprisingly also includes B. rigidum, which itself has a unique type of leaf venation. The other major clade comprises most of the species studied, all of which have parallel-veined leaves. These results do not agree with any previous classifications of the genus. Relationships within the major clades are not fully resolved, and a larger sampling and further data from other gene regions is required. Nevertheless, three other strongly supported clades were identified; one of these clades correspond to a group that includes all NW African endemic species, and the low nucleotide variation in this group suggests a recent radiation. The S African B. mundii seems to be a neoendemic closely related to B. falcatum, an Eurasian species.

Key words: Apiaceae, Apioideae, Bupleurum, ITS nrDNA, molecular phylogeny