Chemical composition of the essential oil of the Greek endemic species Marrubium thessalum (Lamiaceae)

Abstract

The genus Marrubium comprises approximately 30 species, indigenous in Europe, the Mediterranean area and Asia [1]. Marrubium thessalum Boiss. & Heldr. is a Greek endemic species distributed in mountain pastures of central Greece (Thessalia) [2]. The species was collected during the flowering time and the essential oil was obtained by steam distillation [3]. The composition of the volatile constituents was established by GC and GC-MS analyses. The steam distillation of the aerial parts of M. thessalum gave pale yellowish mobile oil in 0.03% (w/w) yield. Thirty compounds were identified, representing 92.5% of the total oil, which was characterized by the absence of monoterpenes. Caryophyllene oxide (21.7%), β-caryophyllene (17.6%), germacrene D (15.3%), β-bisabolene (12.6%) and trans-β-farnesene (8.1%) were found to be the main components. Sesquiterpene hydrocarbons (60.0%) constituted the major portion of the oil, compared to oxygenated sesquiterpenes (29.6%) and other constituents (2.9%). Previous studies revealed that β-caryophyllene is also the main compound of M. velutinum oil [4], while this compound and its oxide are the main compounds of M. cylleneum oil; both plants growing wild in Greece [5]. In agreement with previous reports, the genus Marrubium seems to be oil-poor. M. thessalum appears to possess oil that is rich in sesquiterpene hydrocarbons and deficient in odouriferous oxygenated compounds [4].