Ph.D. / Pimelea Banks & Sol. Ex Gaertn. nom. cons. is a large genus consisting of 110 species, of which 90 species are endemic to Australia, 19 to New Zealand and one to Lord Howe Island. The genus has a great diversity of life forms, breeding systems and habitat. Its closest related genus is Thecanthes Wikstr. Thecanthes comprises five species of annual herbs occurring in the Philippines, New Ireland and northern Australia. Australasian Thecanthes and Pimelea are the only genera within sub-tribe Pimeleinae (angiosperm family Thymelaeaceae) and are characterised by the reduction to two stamens. Here I present the most comprehensive molecular phylogenetic study for Pimelea and Thecanthes. Sequences data from nuclear ITS rDNA and plastid rbcL, rps16, matK and trnL-F intergeneric spacer were used to reconstruct a phylogeny for these genera. I have produced 457 new DNA sequences (five genes and 150 taxa) for the present analyses. The resulting phylogeny was used to assess the taxonomic status of Thecanthes and to evaluate the relationships with Pimeleinae since previous studies indicated a close relationship between Pimelea, Thecanthes and species of Gnidia L. from tropical Africa. The morphological delimitation of sections within Pimelea, the biogeography and the radiation of the genus have been revaluated. Pimelea was found to be monophyletic. It was concluded that Pimelea and Thecanthes are congeneric; consequently a paper has been submitted transferring all species of Thecanthes into Pimelea and making the new combination Pimelea filifolia (Rye) Motsi & Rye. Data analysis revealed very low sequence variation within the subtribe Pimeleinae. This suggested a rapid radiation of the genera, which was confirmed by my molecular dating analyses. Based on molecular clock techniques, I calculated the following ages for the origin of Pimelea: 4.1 mya for New Zealand Pimelea spp. and 13.38 mya for other Pimelea spp. The molecular data also indicated that Pimelea and South Africa Gnidia have a direct common ancestor. I also show that the New Zealand Pimelea are derived and dispersed from Australian