Cytogeography of 'Eremophila longifolia' (F. Muell) (Scrophulariaceae) Essential Oil Chemotypes in Australia (BV 61)

Abstract

Previous studies have demonstrated that the Australian Aboriginal medicinal plant 'Eremophila longifolia' displays an extensive variety of essential oil types. These range from those exhibiting exceptionally high oil yields to those yielding no oil at all. In the 1960's the reputation of 'E. longifolia' as a medicinal plant, was sullied somewhat when essential oil analysis of a population in remote Western Australia revealed a high yielding phenylpropanoid rich oil (5.5% w/w of wet leaves), made up predominantly of safrole and methyl eugenol ether, both of which are suspected hepatotoxic carcinogens. Subsequent analysis since that time has revealed at least 4 other chemotypes in New South Wales: type A, made up of isomenthone/menthone with a yield of 4-7% of wet leaves ; type B, made up of karahanaenone with a yield of 0.5-5%; type C, made up of various monoterpenes and monoterpenols including borneol and fenchol, with a yield of 0.2-0.7%; and type D, made up of various monoterpenes such as a-pinene, sabinene and limonene, with a yield of 0.0-02%. Recently relative flow cytometric analysis, coupled with chromosome counts conducted earlier, has demonstrated that chemotypes with exceptionally high essential oil yields, such as the type A and B chemotypes in New South Wales, and the phenylpropanoid chemotype in Western Australia, are diploid whereas all others are tetraploid. Of particular interest, the higher yielding type B specimens, found in a significant geographically confined area, are diploid and the lower yielding specimens found elsewhere are tetraploid. We hypothesise that ploidy analysis is a significant area for further research in essential oil biosynthesis.