Abstract
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