Composition and allelopathic effect of the essential oils of two thistles: Cirsium creticum (Lam.) D.’Urv. ssp. triumfetti (Lacaita) Werner and Carduus nutans L.

Cirsium and Carduus are two of the main genera of true thistles. Different species in these genera share a quantity of secondary metabolites and have interesting ecological properties. The essential oils of two species, Cirsium creticum and Carduus nutans, were analysed, showing the presence as main compounds of 4-ethyl guaiacol (15%), hexadecanoic acid (10.6%), (E)-β-damascenone (7.8%), dihydroactinidiolide (6.0%) and 4-vinyl guaiacol (4.5%) for C. creticum and hexadecanoic acid (18.6%), hexahydrofarnesylacetone (7.8%), heptacosane (5.9%), 4-vinyl guaiacol (5.8%), pentacosane (3.8%) and eugenol (3.6%) for C. nutans. The oils were evaluated at different doses for their effect on germination and initial radical elongation of three species, Raphanus sativus L. (radish), Lactuca sativa L. (lettuce), and Lepidium sativum L. (garden cress), usually utilized in allelopathic assays: they showed a weak inhibitory activity against seed germination and radical elongation of the three test species.