Peltate Glandular Trichomes in Relation to Their Parameters, Essential Oil Amount, Chemotype, Plant Sex and Habitat Characteristics in Thymus pulegioides

The parameters and plant habitat characteristics of glandular trichomes could allow for faster and cheaper identification and selection of more essential oil-rich wild aromatic plants for further cultivation. This study aimed to establish relationships between the parameters of peltate glandular trichomes and essential oil content in commercially potential Thymus pulegioides in relation to plant sex, chemotype, and habitat characteristics. In total, 124 T. pulegioides plants belonging to different chemotypes and sexes and collected from 23 natural habitats were analysed. Essential oils were extracted by hydrodistillation, and a light microscope was used to investigate parameters of peltate glandular trichomes in upper and lower leaf epidermises. For investigation of the dynamics of the parameters of peltate glandular trichomes, T. pulegioides were growing in open ground under the same environmental conditions. Results demonstrated that the essential oil percentage in phenolic chemotype plants was higher than in plants of a non-phenolic chemotype. Females and hermaphrodites did not significantly differ according to essential oil percentage. Cover abundance of T. pulegioides negatively affects the density and diameter of peltate glandular trichomes and the essential oil percentage in T. pulegioides. The parameters of peltate trichomes in the upper leaf epidermis could be anatomical markers, helping to select T. pulegioides with higher essential oil contents from natural habitats as promising candidates as new crops.