A Comparison of Volatile Components Across Native Australian Mentha (Lamiaceae)

Mentha are historically important regarding their volatile oils. Since limited accounts exist for Australian species, we document the variation in volatiles across all Australian Mentha species, using the GC/MS of pentane extractions from leaf samples of replicate populations for all known species. Oil yields were consistently poor (<0.2% w/w) for freshly dried and herbarium specimens. Many species uniformly had high percentages of volatiles characteristically attributed to Mentha (viz. Menthone, Pulegone); yet, others-consistently or variably-lacked them. Mentha australis had the highest concentrations of menthone (25%), isomenthone, (9%) and pulegone (24%), and M. diemenica had menthone (32.5%) and pulegone (29.8%). Extracts from M. grandiflora from herbarium specimens produced weak traces, high in menthone and pulegone. Mentha satureioides had the highest menthone (20-30%) and pulegone (22-28%) in populations across the extent of its range; yet, an entirely different chemotype was identified from eastern New South Wales that contained limonene (17%), 1,8-cineole (19%), and α-terpineol (8%). Mentha laxiflora consistently exhibited limonene (27%); yet, the levels of the other main components (e.g., menthone, β-pinene, germacrene-D, and bicyclogermacrene) varied across populations. Mentha atrolilacina exhibited the most unique oil profile, with main components consisting of linalool (21%), β-caryophyllene (14%), germacrene-D (14%), and bicyclogermacrene (23.7%). Commercial samples of M. satureioides were found only to be the chemotype high in limonene (17%) and 1,8-cineole, which warrants further taxonomic research and caution for the industry seeking mint flavours from Australian sources.