Variation in essential oil composition of isolated leaves, isolated stems and leaves + stems of Haplophyllum tuberculatum was studied at the three developmental stages during a one-year phenological cycle. GCâMS analysis showed qualitative and quantitative variation over the phenological cycle. The main components were limonene (7.35â14.34%), Î±-phellandrene (7.14â11.87%), 2,4-bis(1,1-dimethylethyl)-phenol (2.52â11.56%), trans-p-menth-2-en-1-ol (7.46â10.83%), Î´-3-carene (8.33â10.41%), piperitone (2.33â9.42%) and myrcene (4.91â8.25%), where their percentages varied according to the developmental stage of growth. The results from HCA and PCA revealed a clear discrimination between the three studied developmental stages. Essential oils at flowering and fruiting stages showed higher antimicrobial activity than those at vegetative stage. The highest antioxidant activity was also exhibited by essential oils at flowering and fruiting stages. The present findings allowed choosing the best organ with the optimal harvesting period to have the highest effectiveness of essential oil in terms of biological activities.