Thymus pannonicus
Thymus pannonicus, known by its common name Hungarian thyme or Eurasian thyme, is a perennial herbaceous plant, distributed in central and eastern Europe and Russia. It grows over open dry meadows, grasslands, and rocks. In Serbia, this plant species contributes to several xerothermous grass formations which develop on warm, dry silicate terrains at altitude above , mostly over plains or mild slopes, on acidic soils derived from crystalline albite-muscovite schist and gneiss-like granite. In southern Banat (Serbia), the dried herb is used to make tasty and refreshing herbal tea drinks, owing to its peculiar and pleasant lemon -like scent. Fresh leaves are used for aromatisation of homemade jams, candies and similar confections. Traditionally, it is used also for coughs and other respiratory complaints, as well as certain gastrointestinal disorders. Chemical composition. According to Karuza-Stojaković et al., the principal constituents of "T. pannonicus" essential oil from southern parts of Vojvodina province (northern Serbia) were terpinyl acetate, terpinen-4-ol, thymol, carvacrol, and geranyl acetate (listed in order of descending quantity). Recent comprehensive studies of chemical variability in hydrodistilled essential oils of different wild growing and cultivated populations of "T. pannonicus" from Hungary, as well as supercritical fluid extracts  of various "Lamiaceae" species, confirmed that high concentrations of both thymol and p-cymene are the main chemosystematic attributes of "T. pannonicus" essential oil. Further research efforts of Pluhár Zs. et al. on the volatile oil composition of "T. pannonicus" from nineteen different localities of Hungary, confirmed a significant essential oil polymorphism in this plant species, as twelve different chemovarieties were determined, namely: thymol, thymol/p-cymene, thymol/p-cymene/γ-terpinene, thymol/p-cymene/neral, thymol/p-cymene/γ-terpinene/β-bisabolene, thymol/p-cymene/isoborneol/γ-terpinene, thymol/linalyl acetate/γ-terpinene/α-cubebene, p-cymene/geraniol/linalyl  acetate, linalyl acetate/geranyl acetate, germacrene D/β-caryophyllene, caryophyllene oxide/α-cubebene/linalool, and germacrene D/β-caryophyllene/farnesol. On the other hand, a "T. pannonicus" population, which is located over the southern slopes of Vršac Mountains in southern Banat (Vojvodina province, Serbia) was characterised by exceptionally high percentage of oxygenated monoterpenes (91.75%). The most abundant components of its essential oil were identified as geranial (41.42%, w/w) and neral (29.61%, w/w), the mixture of which is frequently referred to as citral. Biological activity. The antimicrobial activity of essential oil was evaluated using the agar disc diffusion and  broth microdilution methods against "Staphylococcus aureus", "Enterococcus faecalis", "Pseudomonas aeruginosa", "Escherichia coli", two strains of "Klebsiella pneumoniae" and two strains of "Candida albicans". The essential oil exhibited "in vitro" antimicrobial activity to varying degrees against all tested strains. The maximum activity of "T. pannonicus" oil was observed against "E. coli", "S. aureus" and both tested strains of "C. albicans" (MIC = 50 μl/ml, each). Moderate activity was observed against "P. aeruginosa" and one of the tested strains of "K. pneumoniae" (MIC = 200 μl/ml), while "E. faecalis" and the other strain of "K. pneumoniae" expressed a higher degree  of resistance (MIC > 200 μl/ml))