Thymus from Lamiaceae contains different species with variable chemical constituents. These species are rich in monoterpenoid phenols, which contain important constituents such as thymol and carvacrol. Khorasan thyme (Thymus transcaspicus Klokov) is native to Iran and Turkmenistan with a limited distribution in the Northeast of Iran from 1700 to 2800 m altitude . Although this species is native to Iran, there is not much information on the chemical composition, particularly its essential oil constituents. The rusults showed the range of essential oils was from 1.2% to 2.3% in different habitats, with the highest in Tiwan (2.3%). In general, 51 constituents were identified in the essential oils that with 43 in Reiin, 36 in Pakotal, 43 in Laeen Kohneh, and 40 in Tiwan. The thymol content for Pakotal, Laeen Kohneh, and Reiin were 54.3, 45.3, and 44.9%, respectively, and these values were 8.4, 13.1, and 13.3% for carvacrol. Based on these findings, two distinct chemotypes were recognized, where the thymol chemotype was from Pakotal, Laeen Kohneh, and Tiwan, and the carvacrol chemotype was from Reiin. These differences can be associated with the probable hybridization of different species in the area.The thymol concentration was positively correlated with humus and Na, K, Mg, and Cd contents of the soil. In our investigation a comparison was made between essential oils from wild and cultivated plants (samples were taken from a separate experiment) and it was found that the cultivated plants had 25 constituents, which was 98.2% of the total essential oil content. In conclusion, the essential oils of T. transcaspicus from different habitats varied (1.3–2.3%), possibly due to different environmental conditions, and two distinct chemotypes were identified. Thymol and carvacrol were the main constituents, and plants from natural habitats contained higher amounts.

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