The origin of the flora of the Macaronesian archipelagos has been a subject of controversy for over a century with the traditional opinion asserting that it is a relictual fragment of a widespread Tertiary subtropical European flora. A phylogenetic investigation of the three Macaronesian genera of the Bencomia alliance (Bencomia, Dendriopoterium, and Marcetella) using sequence data from the nuclear rDNA Transcribed Spacer region (ITS) has provided evidence relevant to the origin of the Macaronesian flora and the evolution of morphological characters of interest to students of island biology. In the ITS phylogeny, the Bencomia alliance, Sarcopoterium, a monotypic genus of the eastern Mediterranean, and Sanguisorba ancistroides, also a Mediterranean species, form a clade that is sister to the Eurasian Sanguisorba minor. These relationships contradict the relictual hypotheses and show that the endemic Macaronesian Rosaceae are sister to Mediterranean Sanguisorbeae. The data also contradict a recent placement of Dendriopoterium and Marcetella together in a subgenus of Sanguisorba. The ITS tree demonstrates that dioecy evolved in the islands from a continental monoecious or gynomonecious ancestor and that there has been an increase in plant size and woodiness compared to continental relatives rather than the decrease suggested by previous workers.

Communicating Editor: Matt Lavin