Introduction to the flora, life form and plant geographical distribution in the steppic rangelands (Case study: Khod – niok catchment in yazd province, Iran)

The Studied region located in NW of Yazd in Yazd province. The lowest and highest altitudes of the area are 1530 and 3260 m, respectively. Average annual precipitation in ten years period (1998-2007) reaches to 98 mm that lowest and highest are 32 and 205 mm, respectively. Flora of this area includes 255 plant species that belong to 168 genera and 44 families. The important families are include : Asteraceae with 41 species (16%), Papilionaceae and Brassicaceae with 26 species, Poaceace with 22 species, Lamiaceae with 21 species ,Chenopodiaceae with 20 species, Apiaceae and Caryophyllaceae with 10 species , Boraginaceae with 9 species and Eupphorbiaceae with 6 species, respectively. Life forms of the plant species of the area include: Hemicryptophytes 94 species (381%), Therophytes 24%, Chamaephytes 18%, Phanerophytes 10% and Geophyte 10%. From the view point of chorology plants of this region include: 68.6% Irano-Turanian, 14.1% Irano- Turanian and Saharo-Sindian, 5.9% Irano- Turanian and Mediterranean, 3.9% Irano-Touranian and Mediterranean and Saharo- Sindian 3.1% cosmopolitan , 2.4% Irano- Turanian and Euro- Siberian , 1.2% Irano-Touranian and Mediterranean and Euro-Siberian and 0.8% Irano-Turanian and Euro-Siberian and Saharo-Sindian determined. From the 255 species of flora in this area, 44 species are endemic in Iran and two of these species include: Helichrysum davisianum and Hymenocrater yazdianus are endemic in Yazd.