9801594 Jansen Under the direction of Dr. Robert Jansen at the University of Texas, graduate student Janet Barber is studying the origin and evolution of the plant subgenus Marrubiastrum in the genus Sideritis (family Lamiaceae). This group contains 24 perennial species found only in the Macaronesian archipelagos of the Canary Islands and Madeira. These plants display great variety in morphological form and, except for a few species, generally have highly restricted distributions on single islands. Yet as a group they have exploited all of the diverse ecological zones present in the two archipelagos. The subgenus exhibits extensive chromosomal aneuploidy, a type of change in chromosome number considered rare for perennial plants in general and island plants in particular. Morphology of the group is well-understood due to a recent (1992) revision of the subgenus, but evolutionary relationships among the species are not known. It has been suggested that the Macaronesian members of Sideritis are most closely related to species from the eastern Mediterranean region, but there is no phylogenetic support for this assertion. In addition, it is not known whether the island taxa are derived from their continental relatives, or if the mainland species may have been reintroduced from the islands following Pleistocene glacial episodes on the continent. The proposed study will develop a phylogeny for the subgenus using molecular markers. This inferred evolutionary schema will show whether the island taxa form a cohesive evolutionary group, implying a single introduction to the region. It will identify the closest continental relatives and will indicate the direction of migration. It will also test the hypothesis of a biogeographic link between Macaronesia and the eastern Mediterranean. Mapping of chromosome number and geographical and ecological distribution onto the phylogenetic tree will permit interpretation of the roles of these factors in the evolution of the subgenus within the islands. As the first study to apply molecular techniques to a group in the Lamiaceae of the Atlantic archipelagos, this work will complement studies in other plant families that have documented evolutionary patterns unique to Macaronesia and will make a significant contribution to understanding the origin and evolution of its flora.
