| Summary: | To ascertain phylogenetic relationships in the genus, the ITS region (internal transcribed spacers) of 18-26S nuclear ribosomal DNA repeat was sequenced for 32 species (35 taxa) of <I>Bupleurum </I>(31 species sequenced for the first time). Sequences were obtained from all the species of the area study, with the exception of two (one a doubtful taxon). Taxa from all the currently most generally accepted sections (<I>Bupleurum, Reticulata, Diaphyllum, Isophyllum </I>and <I>Tenoria</I>) and subsections of the genus were included. As an outgroup, sequences of two species of another basal genus of <I>Apioideae,</I> <I>Anginon</I> Raf., were also obtained. In total 68 samples were sequenced which allowed confirmation of sequence by replication for several of the taxa, and provided information on the number of nucleotide changes found within taxon. A phylogeny derived from cladistic analysis of the aligned ITS sequences clearly shows the division of the genus in two main clades (100% supported in the strict consensus tree). This division is supported also by the analysis of the 5.8S sequence alone (conserved gene between ITS1 and ITS2). Based on these results, which are almost completely supported by morphological characters, two new subgenera are proposed: <I>Bupleurum </I>and <I>Penninervia comb. nov. </I>The proposed new subgenus <I>Penninervia, </I>a more basal group, includes all pinnate-reticulate veined species of the genus (<I>B. angulosum </I>L., <I>B. foliosum </I>Salzm. ex DC., <I>B. fruticosum </I>L., <I>B. gibraltarium </I>Lam. and <I>B. stellatum </I>L.), and also <I>B. rigidum </I>that has itself a unique type of venation. The association of these species has never been proposed before (not even the pinnate-reticulate species alone). Subgenus <I>Bupleurum</I>, as defined here, includes all the taxa with typical parallel-veined leaves, and represents the vast majority of the species of the genus. The groups presented within each subgenus are informally treated as neither morphological or sequence data are conclusive and therefore no formal rank is attributed. Final cladistic analysis including sequences from 4 other basal <I>Apioideae </I>genera (outgroup: <I>Anginon, Heteromorpha </I>Cham. and Schltdl., <I>Pleurospermum </I>Hoffm. and <I>Physospermum </I>Cusson ex Jussieu), confirms <I>Bupleurum </I>as a monophyletic group. In this analysis, <I>Heteromorpha </I>appears as the closest genus, with <I>Anginon </I>being the most divergent.
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