Abstract
The essential oils from two members of the Asteraceae (Acanthospermum hispidum DC. aerial parts, and leaves of Tithonia diversifolia (Hemsley) A. Gray), growing wild in Osun State, Nigeria, have been characterised by combined gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analyses. Twenty-nine components have been fully identified and grouped into monoterpene hydrocarbons (22.2%), oxygenated monoterpenes (4.6%), sesquiterpenes hydrocarbons (58.2%) and oxygenated sesquiterpenes (10.8%) in A. hispidum. The main constituents of the oil were β-caryophyllene (28.0%), α-pinene (15.9%) and bicyclogermacrene (11.0%) among the hydrocarbon compounds, and bisabolol (8.9%) and carvacrol methyl ether (4.1%) among the oxygenated components. Tithonia diversifolia essential oil comprised seventeen components and was characterised by a predominant content of monoterpene hydrocarbons (87.9%), cis-β-ocimene (43.7%), α-pinene (28.6%) and limonene (12.0%) being the main compounds. Sesquiterpenes represented ca. 10% oil, as sum of hydrocarbons and oxygenated components. A new chemotype is established for T. diversifolia, while the Nigerian A. hispidum is being reported for the first time as a new source of essential oil with some distinction in composition from those of other sources.