The genus Nepeta with the common Persian name “Pune-Sa” is one of the most important genera of Lamiaceae family. More than 250 species in the world and 67 annual or perennial species in Iran have been reported [1]. Some of these species are valuable in medicine and they used for medicinal purposes. The aim of this study is to identify essential oil content and its chemical composition in pre-flowering, flowering and seed set steps. The samples of N. glomerulosa in these three mentioned steps were collected from Abade region of Fars Province. The essential oils were separately obtained by hydrodistillation and analyzed by GC and GC/MS. Essential oils of the plants in pre-flowering, flowering and seed set stage including 55, 53 and 53 components respectively, that geranyl acetate (16.644%, 18.182% and 24.441%), geraniol (10.797%, 11.372% and 12.389%), caryophyllene oxide (8.302%, 10.515% and 6.661%), humulene epoxide ΙΙ (7.974%, 7.112% and 2.587%), α-pinene (4.743%, 4.126% and 6.724%), limonene (4.086%, 3.848% and 4.711%) and 1,8-cineol (3.397%, 4.609% and 3.759%) were the major components of the essential oil. The results confirmed that phenological stages have a significant effect on essential oils constituents and geranyl acetate and geraniol increased by development of plant from vegetative to seed set stage and geranyl acetate is the main essential oils constituent of the plants during three phonological stages

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