Sideritis L. (Lamiaceae) comprises approximately 150 species of annuals and perennials distributed chiefly in the Mediterranean region. Twenty-four of these are woody perennials endemic to the Macaronesian archipelagos of Madeira and the Canary Islands. An earlier study used a chloroplast DNA restriction site approach to elucidate the pattern of evolution within and among the islands. In an effort to determine the continental origin of the insular group, we sequenced the trnL intron and the trnT-trnL intergenic spacer of the chloroplast genome. Sampling included seven island taxa, drawn from all three sections of the Macaronesian subgenus Marrubiastrum, and 29 continental taxa representing the remaining four sections that comprise the continental subgenus Sideritis. The two perennial continental sections form strongly supported clades, but there is little resolution within the groups. While the Macaronesian subgenus Marrubiastrum is monophyletic, its sections are not; this finding agrees with the results of the earlier cpDNA RFLP study. The cpDNA sequence data identified Sideritis cossoniana, an annual species from Morocco, as the closest continental relative of the Macaronesian group. Preliminary analyses of ITS sequences for the same taxa corroborate this relationship, which contrasts with the hypothesis of earlier workers who suggested that the insular taxa were most closely related to eastern Mediterranean species of the genus. This study provides further evidence for the evolution of woodiness in insular taxa descended from herbaceous continental ancestors.

Key words: biogeography, Lamiaceae, Macaronesia, Sideritis