Dissertation Research: Biosystematics and Evolution of the Genus Brachylaena R. Brown (Comlpositae)

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Brachylaena (Compositae) is a woody, dioecious genus of thirteen species; it is distinct from other members of the Compositae and is considered to represent a monophyletic assemblage. Five of the species of Brachylaena are endemic to Madagascar and the Mascarene Islands while eight species are confined to the continent of Africa. The PIs propose to test some of the proposed origins and affinities of the Madagascar Flora using Brachylaena as an exemplar. The genus is distributed between the two regions and it is widespread on the Island of Madagascar, suggesting an ancient affinity. Several taxonomic problems such as intergrading morphological forms have been recognized in the genus therefore, it is proposed that an initial phenetic analysis be carried out to establish the limits of the groups. The groups obtained from this analysis will then be compared electrophoretically to determine the genetic variation within and among populations of individual species and to estimate the genetic divergence among species of the genus. Only two chromosome counts have been made for the genus but it appears from these that at least one of the species is tetraploid. In addition to phenetics and electrophoresis, an analysis of restriction site data from chloroplast DNA will be undertaken in order to produce a phylogenetic hypothesis for the genus. This will be compared to a cladogram generated from morphology. The distribution of Brachylaena, with certain species restricted to the continent of Africa and others endemic to Madagascar, will make it possible to discuss the evolution of this group in the context of the two regions and to relate this to known geological events. Furthermore, aspects of the biology and distribution of this genus (i.e., woody, dioecious and tropical) make it an interesting and important group in which to study genetic variation within and among populations.