Intergeneric hybridisation in New Zealand Gnaphalieae (Compositae)
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The occurrence of natural intergeneric hybridisation among the New Zealand Gnaphalieae was investigated using a case study approach. Putative hybrids between Anaphalioides bellidioides and Ewartia sinclairii were collected from beside the Yeo Stream, Inland Kaikoura Range, Marlborough and putative hybrids between Leucogenes grandiceps and Raoulia eximia from Mount Hutt, Mount Hutt Range, Canterbury. Cytology, pollen stainability and experimental crosses provided evidence for reduced fertility in the putative hybrids. Field evidence and the morphology and leaf anatomy of the putative hybrids supported the hybridity hypotheses for the majority of the putative hybrids. A range of isolating mechanisms may restrict the frequency of these hybrids in the field. In particular, environmental factors (the availability of suitable habitats and natural disturbance) and pre-zygotic and post-zygotic barriers (embryo and/or endosperm abortion, hybrid fitness and hybrid fertility) were suggested to be important. Cross-compatibility among indigenous Gnaphalieae and with related exotic Gnaphalieae was investigated through artificial crosses. Individual plants from six indigenous and five exotic species were preferentially selected as parents. The results provided evidence for the cross compatibility of many indigenous Gnaphalieae, including species of Anaphalioides, Euchiton, Ewartia, Helichrysum , Leucogenes and Raoulia. A plant of Euchiton audax was cross-compatible with individual plants of Ewartia planchonii and Gamochaeta spicata. The results indicate species groups among the indigenous Gnaphalieae are less genetically distinct than morphology suggests. The partial fertility of some natural intergeneric hybrids suggests intergeneric gene exchange has a potential role in the future evolution of the group.