This study aimed to investigate plant species diversity in the ecological species group in relation to the environmental factors. A study area of 216 ha in the southeast of Baghmalek on which seventy 20×20 m plots were established according to the random-systematic method was selected. Soil properties and physiographic factors were recorded at each plot. Herbaceous species composition was recorded using four 1×1 m subplots around the center of the main plot. A cluster analysis and a CCA analysis were undertaken and three ecological groups were identified. The results showed that pH, Nitrogen, cation exchange capacity, organic carbon and clay percentage were the most important factors of the first group, and the indicator species were, Agropyrom trichophorum, Hordeum bulbosum, Aegilops triuncialis. The second group with  Bromus tectorum, Salvia macrosiphon, Bromus danthonia as indicator species could be correlated with clay, organic carbon, Potassium, Phosphorous, Nitrogen, values. Lastly, the third group, characterized by Artemisia aucheri, Astragalus gossypinus, Phlomis persica, Artemisia haussknechtii as the indicator species, could be correlated with the elevation percentage of sand, Bulk Density and EC. We also found that species diversity varied significantly among the groups, and it was the highest in the first group and the lowest in the third group. The results could, therefore, contribute to better evaluation of species diversity and management of the biodiversity.