Journal of Plant Process and Function

                 Achillea is flowering plants in the family of Asteraceae that is one of the most important medicinal plants. A. millefolium is one of the important species and a best-known source of antioxidant activity. In this study, essential oil yield and composition of total phenolic, flavonoid content and antioxidant activity (1,1-diphenyl-2-picrylhydrazyl and ferric thiocyanate model systems) of Amk from kandowan, AmlitR from Lithuania, AmUK from the British, Amo from Orumie and Amh from Hamedan were investigated in four phenological stages including five leaves appearance, sprouting, 50% and 100% flowering. An experiment was performed at Isfahan University of Technology in split plot in time, while a completely randomized block design with three replicates used to analyze the data. Results indicated that phenolic compounds, flavonioid content and ferric thiocyanate model system (in concentration from 50 ppm to 500 ppm) increased as the plant growth elevated until 50% of flowering, while it decreased in the maturity stage in all genotypes. For total phenolic and flavonioid content, the highest and the lowest amount observed in Kandovan (84.52 mg/1g of dry weight) and Orumie (13.936 mg Quercetin/gdW) genotypes, respectively. For reducing power, the highest absorbance in 700 nm belonged to Kandovan and in DPPH assay, Kandovan showed the lowest Ic50 (639.165 μg/ml). For essential oil yield, the highest and the lowest percent belonged to AmlitR (0.07%) and Hamedan (0.7%) at 100% flowering, respectively. So, the best harvesting time for this species in respect to total phenolic compounds was 50% flowering, while the best time for gaining high essential oil yield was 100% flowering.