Mentha (Nepetoideae, Lamiaceae) is a taxonomically complex genus that includes economically important members such as spearmint (M. spicata) and peppermint (M. x piperita) and species of global conservation interest (M. gattefossei and M. requienii). Mentha is considered challenging systematically due to its high incidence of polyploidy, diverse morphology, variation in base chromosome number, and frequent interspecific hybridization. Therefore, our goals are to test the monophyly of Mentha and each of its traditionally recognized sections and assess phylogenetic relationships of the Mentha species and selected hybrids using DNA sequence data from the chloroplast TrnL-TrnF and nrITS regions. Total cellular DNA from 15 Mentha species representing all five sections (Audibertia, Australasica, Mentha, Preslia, and Pulegium), two named hybrids, and two outgroups have been isolated. The TrnL-TrnF region was PCR amplified and sequenced in all samples; however, we have only sequenced the ITS region for three species so far. The phylogenetic relationships within Mentha based on TrnL-TrnF data were reconstructed using parsimony. The results strongly support the monophyly of Mentha. However, neither the species of sect. Australasica nor those of sect. Mentha form monophyletic groups and are therefore inconsistent with traditional classifications. Four of the five species (M. australis, M. cunninghamii, M. diemenica, and M. satureoides) of sect. Australasica from Australia, Tasmania, and New Zealand form a well supported clade (84%), but the fifth member, M. japonica, from Japan is more closely related to species in other sections. Although species of sect. Mentha form a weakly supported group, this clade also includes the remaining species representing four sections. There is also a close relationship between M. pulegium (sect. Pulegium) and M. requienii (sect. Audibertia). The positions of both major economic plants, M. spicata (a stabilized ancient allopolyploid) and M. x piperita are consistent with their hybrid origins.

Key words: ITS, Lamiaceae, Mentha, phylogeny, systematics, TrnL-TrnF