Origin and biogeography of New Zealand Craspedia (Compositae: Gnaphalieae)
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Craspedia (Compositae: Gnaphalieae) is a genus of 23 species found only in Australia and New Zealand. New Zealand species of Craspedia have confusing and continuous character variation, with boundaries between species often indistinct and relationships difficult to elucidate. Taxonomic treatments in the genus so far have been regionally based, with the result that species between New Zealand and Australia have not been adequately compared. Phylogenetic analyses of ITS, ETS and psbA-trnH non-coding spacers show that New Zealand Craspedia is a monophyletic group nested within Australian Craspedia. This is consistent with a jump-dispersal event from Australia to New Zealand across the Tasman Sea. The New Zealand lineage is identified as sister to one of two Australian lineages, which consists of mainly subalpine and alpine species found on the main divide of south eastern Australia and in Tasmania. An estimate of when New Zealand Craspedia diverged, using ITS substitution rates from other mainland/island disjunctions in Compositae, gave an approximate date of between 650,000 and 325,000 years ago. This is consistent with the New Zealand fossil pollen record, and with other molecular studies, in suggesting that the Pleistocene, a period of mountain building and climate change, has been an important factor in the evolution of the New Zealand herbaceous flora. The two Australian lineages have not previously been recognised based on morphology and it is suggested they represent two independent species radiations into the Australian alpine zone. Although the New Zealand clade is only partly resolved, the phylogenetic analyses of ITS and ETS indicate that some relationships are incongruent with those previously suggested by morphology and current species boundaries.