Salvia is the largest genus in the Lamiaceae family, and naturally grows in various parts of the World. This genus is represented in Iran by more than 50 species, which widely distributed in diverse regions of the country. Salvia macrosiphon Boiss., is one of the annual aromatic species of the genus, and creates several natural populations across the country. A wide range of secondary metabolites, such as flavonoids and essential oil, have been extracted from this species. In this regard, several biological properties, including antibacterial, antifungal, and anticancer, have been reported for this species. Additionally, this herb has been employed in traditional medicine to treat different diseases. In the current study, we evaluate anatomical structure in the midrib region in eight natural populations of S. macrosiphon. Three mature and intact leaves were obtained per population, hand cutting slices of leaves were double-stained and examined under Olympus light microscopy, at various magnifications. Results revealed that, all the populations have leaves with a dorsi-ventral structure. A thin layer of epidermis was observed on the dorsal and ventral sides of leaves, which consisted of a single layer of oval to rectangular cells. Moreover, a thin layer of cuticle covered the external surface of cells. A dense indumentum observed on the both leaves sides. The main vein shape was semicircular and in some populations slightly lobed in the ventral side. A thin layer of collenchyma tissue was detected under the epidermis tissue that was composed of 1 to 2 layers. About 7-10 layers of spherical to polygonal parenchyma cells were detected on the dorsal side, while it consisted of 6-8 layers on the ventral side. There were nine and ten cell layers of phloem and xylem tissues on the midrib, respectively. According to these findings, we concluded that the environmental parameters can create anatomical variations in the leaf structure. The induced differences have an adaptive value for plant to survive under various ecological conditions
