John McDonald

Chenopods are the plant group most frequently cited as a component of Australian arid flora derived from a coastal flora. Molecular studies over the last decade indicate several waves of chenopod invasion occurring since the Mid-Miocene, which approximates to when the continent began to aridify. The arid landscape into which chenopods have greatly diversified, formed since the Miocene, so the broad evolutionary patterns of chenopods within Australia should be revealed in comparing landscape development with chenopod diversification from dated molecular phylogeny.

My interest in chenopods (otherwise known as goosefoot, saltbush, bluebush) grew out of employment as Rangeland Ecologist, which required substantial knowledge of the preferred habitats of chenopods and their response to commercial grazing. To some degree, undertaking this Ph. D. is an attempt to organize and extend the thoughts and observations from a previous life. This largely exploratory approach will use molecular methods to develop comprehensive phylogenies for select, supra-specific chenopod taxa, combined with phylogeographic analyses of select chenopod species, to pursue 3 main studies.

Firstly, identifying major clades within molecular phylogenies, and classifying them according to their preferred main habitats. Correlating Stem/Crown age of each clade with its main habitat and formation time should reveal rapid evolution where ages are comparable and slower adaptation where they substantially lag. Secondly, developing a habitat spectrum for each major clade (and sub-clades) indicates the degree to which chenopods followed niche shifting (broad spectrum) or niche conservatism (narrow spectrum) during diversification. Thirdly, some developing landscapes may have been detrimental rather than beneficial to chenopods. Development of dunefields and modern climatic zonation may have caused local extinctions, generating disjunct patterns seen today. Correlating geochronological dunefield age with age of last exchange of genetic material for each disjunct species, would confirm dunefield development as vicariant process.