Essential oils from the Australian Aboriginal medicinal plant 'Eremophila longifolia' (emu bush) were characterised using GC/MS and NMR, and antimicrobial capacity investigated using disc diffusion and broth dilution. Leaves were collected from various locations within New South Wales (NSW, Australia) and hydro-distilled for volatile leaf oils. Overall yield and oil constitution differed markedly according to the geographical region from which the plants were collected. 'E. longifolia' demonstrated a variety of chemotypes not yet recognised. Four further chemotypes are now recognised within NSW, in addition to the two previously characterised from other regions of Australia; the Northern Territory (NT) and the Murchison district in Western Australia (WA). Characterisation of NSW chemotypes revealed that here 'E. longifolia' does not produce the carcinogenic volatile compound, safrole, as previously described in the leaf oil from Murchison specimens (WA). Two separate chemotypes within NSW yielded oil as high as 7% w/w and 3.5% w/w consisting mostly of iso-menthone (70-90%) and karahanaenone (≈80%) respectively; marking these as the most abundant natural sources of these compounds so far described [3,4,5]. The two remaining chemotypes had a much lower yield, 0.2 and 0.7%, and were more similar to the chemotype found in the NT; leaf oils consisting of limonene (≈20%) and borneol (20-30%) respectively. Antimicrobial assays of volatile oils from the four chemotypes revealed a moderate to high antimicrobial capacity, varying with species and chemotype. Traditional (location specific) indigenous applications of the oils are consistent with these results. The essential oil from 'E. longifolia' may thus be a likely candidate for further investigation into cosmeceutical use addressing a similar market niche to that already successfully occupied by the essential oil of 'Melaleuca alternifolia' (tea tree oil) and more recently 'Backhousia citriodora' (lemon myrtle oil). Further investigations (wound healing, anti-inflammatory and cultivar chemotype requirements) are in progress.

'Eremophila longifolia' is a woody shrub, endemic to arid and semi-arid regions of Australia, where it is employed in traditional indigenous medicine to treat a wide variety of conditions. An early report examining 'E. longifolia' leaf essential oil composition had indicated high levels of the hepatotoxic and carcinogenic phenylpropanoid safrole, and as a result, authors have urged caution in the use of traditional preparations derived from this species. The present study was initiated after noting significant variations in morphology and odor profiles of wild 'E. longifolia' specimens in the state of New South Wales, (NSW) Australia. Leaves from several specimens were collected across a range of biogeographic regions in NSW. Essential oils were obtained by hydrodistillation and analysed using GCMS and NMR spectroscopy. Thirty-five compounds were identified with comparison of retention data and mass spectra with that of published values. Considerable variation was found among specimens in essential oil yield and composition, resulting in identification of three distinct types (here designated A, B and C). Type A specimens produced oils at relatively high yields (3.1% - 5.7 %) with major constituents isomenthone (61.1% - 86.7%), menthone (8.8% - 22.6%) and α-terpineol (8.4% - 11.0%). Type B specimens produced oils of relatively moderate yield (0.5% - 1.9% g/g) with major constituents karahanaenone (81.0% - 82.2%) and α -terpineol (4.1% - 11.7%). One specimen (designated type C) produced essential oil at relatively low yield (0.4% g/g fresh leaves) with major constituents identified as borneol (31.7%), fenchol (19.7%) and limonene (9.9%). No phenylpropanoids, including safrole, were detected in any of the specimens examined here. The relatively uncommon monoterpenoid karahanaenone is valued as a precursor in the fragrance industry and to the best of our knowledge the leaves of type B specimens described here represent the richest known natural source of this compound.