Chemotaxonomic significance of volatile compounds in Thymus samius and its related species Thymus atticus and Thymus parnassicus

Thymus samius, a rare species endemic to the island of Samos (East Aegean, Greece), has been considered to be of possible hybrid origin, with Thymus cilicicus, Thymus parnassicus or Thymus zygioides as putative parents. Morphologically it also resembles Thymus atticus. In order to evaluate any possible chemotaxonomic relationships indicated by the qualitative and/or quantitative differentiation of volatile compounds, the essential oils of T. samius, T. parnassicus and T. atticus were analyzed and the oils of T. cilicicus and T. zygioides were used for comparison. T. atticus presents considerable variation in chemical constituents, with all Greek populations being poor in thymol/carvacrol and rich in (E)-nerolidol, germacrene D, (E)-caryophyllene, caryophyllene oxide, 1,8-cineole, α-pinene and camphene, depending on the sample. T. parnassicus shows remarkable qualitative stability in its volatile constituents, and all its populations have a similar profile with (E)-caryophyllene being the most prominent compound. T. samius is characterized by the presence of germacrene D and β-bisabolene, which constitute almost half its oil percentage. This species is also characterized by a low amount of monoterpenes; the latter exist in a considerable percentage in the related species. Our results indicate that T. samius does not show similarity or intermediacy in chemical compounds with any given couple of T. atticus, T. parnassicus, T. cilicicus, or T. zygioides.