An Introduction to the Flora, Life Form and Plant Geographical Distribution of Tirgan Watershed (Khorasan Province)

The extent of area is about 3571 hectars. It is part of Hezarmasjed in north- western Kalat. The average maximum temperture is 20.8 in August and the minimum temperture is -9 in January. A floristic study was done for the area plants and then biological forms and plant chorotypes were identified. In this research, 65 families, 282 genera and 404 species were identified, The largest plant family is Asteraceae with 52 genera and 82 species and the largest genera is Astragalus of Papilionaceae with 19 species. Chief biological forms are: Hemicryptophytes, Therophytes and Cryptophytes. Most of the species (54.45%) belong to Irano -Turanian region.