New Directions in Australian Essential Oil Research: Chemistry, Chemotypology and Chemotaxonomy; The Three C Essentials (O-1)

Abstract

We have initiated several investigations of essential oils from a variety of native Australian plant species aimed at examining the extent and aetiology of essential oil chemovariation. Chemical fingerprints thus derived have been used to complement taxonomic studies aimed at re-evaluating existing species classifications. For example, using relative fluorescence in flow cytometry, significant observed chemotypic variation of 'Eremophila longifolia' has been shown to be consistent with two separate ploidy types; potentially warranting revision of the species. In another example, using NMR and GC-MS to identify some unusual and uncommon essential oil compounds in species of the genus 'Phebalium', we have uncovered a number of taxonomic discrepancies, hitherto suspected but unconfirmed. In particular, dihydrotagetone (2,6-dimethyloct-7-en-4-one) is an omnipresent characteristic of the 'Phebalium glandulosum' subspecies complex; hence other species expressing dihydrotagetone were further examined for morphological characteristics consistent with the 'P. glandulosum' group. Another unusual essential oil ketone, the sesquiterpene squamulosone, was found to be an important complement to taxonomic studies aimed at revising the 'P. squamulosum' subspecies complex. Furthermore, investigation of sesquiterpenoid essential oils from 'Prostanthera' species has uncovered a number of unusual and novel compounds that may also complement future taxonomic studies. Other species, such as those belonging to the genus 'Zieria' and 'Geijera', have also recently been investigated and we shall report on the taxonomic implications of our results and the overall contribution of chemical analysis to a contemporary understanding of the Australian taxa.