This thesis deals with plants from the flowering plant order Lamiales, and especially the two families Scrophulariaceae and Stilbaceae. Both families have their main geographical distribution in southern Africa. The thesis presents phylogenies of Scrophulariaceae s. lat. that can be used as a framework both for a future formal classification of the Scrophulariaceae and of allied taxa.

A new circumscription of the tribe Manuleeae of Scrophulariaceae is presented including also genera earlier placed in the tribe Selagineae (sometimes recognised as a family of its own, Selaginaceae). Manuleeae now consists of the genera: Barthlottia, Chaenostoma, Chenopodiopsis, Dischisma, Glekia, Globulariopsis, Glumicalyx, Gosela, Hebenstretia, Jamesbrittenia, Limosella, Lyperia, Manulea, Manuleopsis, Melanospermum, Phyllopodium, Polycarena, Pseudoselago, Reyemeia, Selago, Strobilopsis, Sutera, Tetraselago, Trieenea and Zaluzianskya. The genera Sutera and Selago are given new circumscriptions; Sutera is divided into two genera, Sutera and Chaenostoma. Selago is circumscribed to contain also taxa that formerly have been placed in Microdon and Cromidon.

A new circumscription and infrafamiliar classification of the family Stilbaceae is also presented. Stilbaceae will consist of the three tribes: Bowkerieae, consisting of the genera Anastrabe, Bowkeria and Ixianthes; Hallerieae, consisting of Charadrophila and Halleria; and Stilbeae, consisting of Nuxia and Stilbe. Furthermore, the genera Campylostachys, Euthystachys, Kogelbergia and Retzia are all included in the genus Stilbe.

The results in the thesis are based on parsimony and Bayesian phylogenetic inferences of DNA sequence data. Further, morphological characters are analysed and compared to the molecular phylogenies.