Ziziphora tenuior L. is an aromatic herb of Labiatae family, which naturally and widely distributed in Iran. In this study, in order to compare the effect of different environmental parameters on trichomes morphology and distribution, three different geographical populations of Z. tenuior were surveyed with (SEM)and (LM) of leaves, calyx and stem.20 trichomes type were described. Digitiform trichomes were of 4 types: 1to 4-celled. 1-celled type was restricted to Saveh and Zarandiyeh and 4-celled type belongs to Madane samples. Conidial trichomes with 2 basal cells could be seen in Saveh and Zarandiyeh samples and sessile type of them were scarce and was restricted to Zarandiyeh samples. Short- stalked capitates hairs with two basal cells and a unicellular head was restricted to Saveh and Zarandiyeh samples and short- stalked capitates with a bicellular head only could be seen in Zarandiyeh samples. Long-stalked capitate trichome with a unicellular globoid head was restricted to Madane and Zarandiyeh populations and long-stalked capitate with a bicellular triangular head was restricted to Saveh samples. Non-glandular trichomes were in two main groups: thin-walled and thick-walled trichomes. Thick-walled trichomes were presented as: triangular and short 2- celled. Thin-walled trichomes were presented as: elongated and flexuose7to11-celled, large 2 to5-celled, pricks-less and short 2 to3- celled. All these types were presented on all populations, but the nature of surface sculpturing was varying among samples. This study show that the soil type was much effective than other ecological factors, such as altitude of growth habit and climate on diversification of plants
