Variation of trichome morphology and essential oil composition of seven Mentha species

Mentha (Lamiaceae) includes several plant species noted for their production of essential oils. The leaf trichome micromorphology of seven Mentha species in China was studied using light and scanning electron microscopy. Non-glandular trichome, peltate glandular trichome and three types of capitate trichome are described. The trichomes varied in structure, distribution, densities and dimensions among the Mentha species. Essential oils (EO) from the blooming stage were extracted by hydrodistillation and the chemical compositions were determined using GC-MS. A total of 51 compounds were detected representing >94.9% of the total EOs. The EO composition is primarily comprised of oxygenated monoterpenes (73.9%-94.8%), monoterpene hydrocarbons (1.0%-21.9%) and sesquiterpene hydrocarbons (0.5%-16.6%). Both PCA and HCA analysis classified the samples as either menthols, carvones, or piperitenone oxides. Trichomes and essential oils were useful systematic criteria for the delimitation of Mentha species.