Volatile compounds in Thymus sect. Teucrioides (Lamiaceae): intraspecific and interspecific diversity, chemotaxonomic significance and exploitation potential.

Thymus sect. Teucrioides comprises three species, namely, T. hartvigii, T. leucospermus, and T. teucrioides, distributed in Greece and Albania. The volatile constituents of all species of the section were obtained by hydrodistillation and investigated by GC-FID and GC/MS analyses. Twenty populations were sampled and a total of 103 compounds were identified, representing 98.0-99.9% of the oil compositions. The oils were mainly characterized by high contents of monoterpene hydrocarbons (42.7-92.4%), with the exception of three oils for which oxygenated monoterpenes were the dominating constituents, viz., that of T. hartvigii ssp. macrocalyx, with linalool as main compound (89.2±0.5%), and those of T. hartvigii ssp. hartvigii and of one population of T. teucrioides ssp. candilicus, containing thymol as major component (46.4±3.1 and 38.2±3.9%, resp.). The most common compound in the oils of the 20 populations of the section was p-cymene. Considerable variation was detected within and among populations, and seven chemotypes were distinguished, i.e., p-cymene, linalool, p-cymene/thymol, p-cymene/γ-terpinene, p-cymene/borneol, p-cymene/γ-terpinene/borneol, and p-cymene/linalool chemotypes. Different chemotypes may exist in the same population. Multivariate statistical analyses enabled the segregation of the oils within Thymus sect. Teucrioides into two groups, one consisting of the three subspecies of T. teucrioides and the second comprising the species T. hartvigii and T. leucospermus. A linalool-rich chemotype, unique within the section, distinguished the oil of T. hartvigii ssp. macrocalyx from all other oils. The high oil content of p-cymene and the preference for serpentine substrates render T. teucrioides species promising for future exploitation.