ABSTRACT Six Achillea species—Achilleadistans, Achillea setacea, Achillea collina, Achillea ageratum, Achillea ligustica and Achillea aspleniifolia—growing spontaneously in North Italy, were studied in order to analyze the oil composition and to characterize the chromosome numbers and karyotypes. A total of 69 compounds were identified from all oils, including monoterpenes and sesquiterpenes. The main oil components of A distans were bisabolene oxide and linalyl oxide, while A. setacea had high percentages of the sesquiterpenes β-eudesmol, α-bisabolol and caryophyllene oxide. A. ageratum was characterized by the presence of artemisia acetate, artemisia alcohol, 1, 8-cineole and yomogi alcohol, whereas A. ligustica had high percentages of artemisia ketone. A. collina and A. aspleniifolia were particularly rich in chamazulene along with good percentages of germacrene D and other sesquiterpene hydrocarbons. A. distans had a hexaploid(2n=54)chromosome number, A. setacea and A. collina a tetraploid (2n=36) chr...