Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Environmental (topography, climate) features have an important influence on plant diversity and richness of Iran. Topography is from –28m which is close to Caspian Sea to 5678m which is located on the Alborz Mountain. Two mountains (Alborz and Zagrosss) prevent moist air moving to the centre of Iran. On the basis of environmental factors, four ecological zones with specific plant richness from lowest area to highest area (Hyrcanian, Khalij-o-Omani, Zagrosss and Iran-o-Touranian zones) were established respectively. These four ecological zones support about 8000 species of flowering plants. Northern Iran is rich in biodiversity with 8000 plant species representative of many different life forms (Herb, Grass, Shrub and tree) in the Hyrcanian zone that is located north of. 35oN latitude. In contrast, the lowest plant diversity is in the southern part of Iran (Khalij-o-Omanian zone), which is a flat area. The vast central plateau (Iran-o-Touranian) is divided into two divisions with mountain part and an area of high plains. The western part of Iran (Zagrosss zone) is affected by Mediterranean and Black sea moisture which brings snow in the winter. The dominant species of this ecoregion are low growing plant species. Topography and climate factors interact to plant influence distribution and richness of Iran and they play an important role in creating microniches that foster great ecological biodiversity of this country.