Maryam Ahvazi - Department of Biology, University of Isfahan, Isfahan ۸۱۷۴۶-۷۳۴۴۱, Iran
Ziba Jamzad - Research Institute of Forest and Rangelands, P.O.Box ۱۳۱۸۵-۱۱۶, Tehran, Iran.
Gholam Reza Balali - Department of Biology, University of Isfahan, Isfahan ۸۱۷۴۶-۷۳۴۴۱, Iran
Hojatolah Saeidi - Department of Biology, University of Isfahan, Isfahan ۸۱۷۴۶-۷۳۴۴۱, Iran.

The genus Marrubium L. belongs to Lamiaceae family and Lamioideae subfamily. Itis present in Iran with ۱۱ species from which only one is endemic (M. procerum Bunge). Most Marrubium species are distributed in steppes, arid and semiarid areas of Iran. In this research the trichomes of leaf and calyx surface were examined using Scanning Electron Microscope. Trichome micro-morphological characters in studiedspecies showed that the main hair type is stellate with unequal rays, one of the rays ۳-۱۵ times longer than the others. The general trichome shapes are similar but there are variations in stellate trichomes based on their long branches length, the short branches length and the number of short branches. The effect of environmental condition i.e. arid areas and altitude are important factors for morphological variations and density of trichomes.

trichome, micromorphology, environmental factors, Marrubium, Lamiaceae, Iran