Four Achillea species, A. millefolium, A. nobilis, A. eriophora and A. biebersteinii, were grown in small field plots in Iran and harvested at four developmental stages: vegetative, at the appearance of the first flower heads, at full flowering, and at late flowering. The composition of the main volatile compounds in dichloromethane extracts of the essential oil obtained by microdistillation was established by GC/MS and GC. 1,8-Cineole (27-41%) was the main compound in the oils from A. millefolium and A. biebersteinii. These two species reached the highest amount of volatile compounds at the full blooming stage. α-Thujone was the main compound in A. nobilis oil (25-64%). Fully blooming plants of this species also had a high proportion of artemisia ketone (up to 40%) in the oil. The main oil compounds of A. eriophora were camphor (about 35%) and 1,8-cineol (about 30%). This species produces only a small number of flower heads and the composition of the essential oil did not change during development

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