Which environmental factors are more important for geographic distributions of Thymus species and their physio-morphological and phytochemical variations?

Little is known about the essential oil content and yield, and physiological and morphological traits of Thymus species including Thymus fedtschenkoi , Thymus kotschyanus , Thymus migricus , and Thymus transcaucasicus . This is the first report on the presence and absence of Thymus species influenced by elevation, precipitation, and temperature. Therefore, the objectives of this study were to investigate the effects of geographical and environmental parameters and species variations on plant growth, quality, and the presence or absence of Thymus populations of Iran. The plants of four different Thymus species were collected at the full flowering stage over 2017 and 2018 from different provinces of Iran. Presence-only modeling method called Maxent was used to predict geographic distributions of species. The impact of climate variability on the qualitative and quantitative properties of populations was higher than the soil physical and chemical characteristics. Temperature was the most important factor that influenced the presence of Thymus species, followed by elevation and precipitation (for T. kotschyanus , the importance of precipitation was greater than elevation). Thymus species are most common in cool to moderate annual temperatures that are elevated enough. Mean total flavonoid in 2018 was higher than that in 2017 across populations due to drought stress. Averaged across locations and years, essential oil yield was in the order of T. kotschyanus > T. migricus > T. fedtschenkoi > T. transcaucasicus . Carvacrol was the main component of T. migricus essential oil from Yam. T. migricus essential oil from Kechi-gala and all populations from T. kotschyanus , T. fedtschenkoi , and T. transcaucasicus had thymol as the main component. The selection of desirable suitable areas and genotypes for cultivation of plants is the first step due to a great effect on the quality and quantity of production.