These 20 species represent collections form the almost world wide distribution of this family. Anatomically all species studied were found to be homogeneous showing a gradual advancement from the most primitive species studied to the most advanced. From a morphological and geographical viewpoint three groups are recognized. The Clethraceae is generally considered to have but one genus, Clethra L. Results of this study show this to be a valid classification. The Clethraceae appears to be monophyletic in origin. Close relatives of the Clethraceae are thought to be the Theaceae and the lower Ericaceae. / Master of Science

Ph.D. / Recent anatomical and molecular studies have highlighted the importance of the African and Malagasy Apiaceae, many of which have been found to occupy early diverging positions within the subfamilies Apioideae and Saniculoideae. Despite the recent interest in the African contingent however, there remain several anomalous and poorly known African and Malagasy taxa in which generic boundaries remain unclear and which have yet to be incorporated within the emerging tribal classification for the family. Generic circumscriptions and affinities amongst hitherto poorly known African and Malagasy genera are here explored using anatomical, cytological, morphological and molecular sequence data. Substantial rearrangements at almost all infrafamilial levels are formalized in order to incorporate the unique African and Malagasy members for the first time. Generic circumscriptions and phylogenetic relationships of the Cape genera Capnophyllum, Dasispermum, and Sonderina are explored through parsimony and Bayesian inference analyses of nrDNA ITS and cpDNA rps16 intron sequences, morphology, and combined molecular and morphological data. The relationship of these genera with the North African genera Krubera and Stoibrax is also assessed. Analyses of both molecular data sets place Capnophyllum, Dasispermum, Sonderina, and the only southern African species of Stoibrax (S. capense) within the newly recognized Lefebvrea Glade of tribe Tordylieae. Capnophyllum is strongly supported as monophyletic and is distantly related to Krubera. The monotypic genus Dasispermum and Stoibrax capense are embedded within a paraphyletic Sonderina. This complex is distantly related to the North African species of Stoibrax in tribe Apieae, in which the type species, Stoibrax dichotomum, occurs. Consequently, Dasispermum is expanded to include both Sonderina and Stoibrax capense. A taxonomic revision of Dasispermum s.l. is presented which includes keys to the species, complete nomenclature, typifications, descriptions as well as geographical distributions. New combinations are formalized for Dasispermum capense, hispidum, D. humile, and D. tenue. In addition two new species, namely D. grandicarpum and D. perrenans, are described. As a result seven species of Dasispermum s.l. are recognised and can be distinguished from one another by their habit (life history and growth form), leaf morphology (leaf texture, leaf colour and breadth of the ultimate leaflet segments), inflorescence structure (length of the peduncle, presence or absence and division of involucre and involucel bracts), fruit morphology (relative length of the styles, fruit size, rib prominence and relative orientation) and fruit anatomy (shape of the cells external to the vittae).