Floristic Composition of the Plants of the Cholistan Desert , Pakistan

A floristic survey of Cholistan desert was carried out during 2009-2011 and total of 38 families, 106 genera and 154 species were documented from the area. Among families, 33 families belong to Dicotyledons of 79 genera and 115 species, while the 38 species of 26 genera belong to 4 families of Monocotyledons and 1 family of gymnosperms with 1 genus and 1 species. The largest family was Poaceae with 34 species followed by Papilionaceae and Zygophyllaceae with 10 species while Asteraceae with 9 species respectively. The life form of plant species was determined by following the Raunkier’s method. Therophytes comprised of 74 species (48%), Chamaephyte 40 species (26%), Hemicryptophyte 18 species (12%), Phanerophyte 19 species (12%) and Cryptophyte 3 species (2%) of the flroa of the area. It will be helpful and serve for the conservation and sustainable utilization of plant resources of the study area.


Introduction
The Cholistan desert covering an area of 26,000 km 2 , lies within South of Bahawalpur in the Punjab extending through the Nara and Thar deserts of Sindh between 27˚42ʹN and 29˚45ʹN latitude and 69˚52ʹE and 75˚24ʹE longitude (Figure 1) [1] at an altitude of about 112 m above sea level [2].
Historically, the Cholistan desert was a cradle of Hakra River Civilization which flowed through the area during 1200 BC regularly and became irregular about 600 BC.Cholistan received heavy monsoon downpours along with the Indus valley civilization including Mohenjo Daro and Harappa of world's oldest civilization about 5000 years ago.Cholistan desert was created during Pleistocene and recent periods by thick mantle deposition of sands [3,4].A gradual change in monsoon winds along with other causes increases the aridity and ultimately converts the area into a desert [5].
The climate of the Cholistan desert is sub-tropical, arid and semi-arid, scorching harsh, with monsoon rainfall influenced by periodic long droughts.The relative humidity is very low with high rate of evaporation [6].The mean annual rainfall varies between 100 mm to 250 mm.The mean summer temperature is 34˚C -38˚C, and the winter temperature is 15˚C -20˚C with highest temperature reaching over 51.6˚C [7].Topographically, the area can be divided into two geomorphic regions based on parent material, soil and vegetation.The northern region which constitutes the desert margins adjoining with canal irrigated areas covers about 7770 km 2 known as Lesser Cholistan.The wind resorted sandy desert covers about 18,130 km 2 in the southern region known as Greater Cholistan [8][9][10].
The soil of the Cholistan desert is very poor in having organic matters.The pH ranges between 8.6 and 10.0 saline and saline-sodic respectively.In Cholistan desert, two sources of water, one is rainfall and other is sub-soil water.Rain water is collected in "Tobas" man-made ponds or natural depression.The second source of water is underground water at the depth of 30 to 90 m.It is brackish and not fit for drinking and agriculture because it contains total dissolved salts about 9000 -27,000 ppm mg/L [11].The vegetation of Cholistan desert comprises of xerophytic species adapted to wide range of severe temperature, moisture and edaphic conditions.The dis- tribution pattern of vegetation depends on the topography and soil chemical composition of the area [12][13][14].
Because of the diverse topographic features and microhabitats, the study area had a great potential for flourishing a rich plant biodiversity.Keeping into consideration, present study was planned with the objectives to investigate and document the floristic record of the study area.It will be helpful and serve for the conservation and sustainable utilization of plant resources of the area.

Materials and Methods
The detailed field studies have been made to collect plant specimens at regular intervals during 2009-2011 in each season.During field visits, 5 plants of each species have been collected, dried and mounted on standard herbarium sheets.The life form of all plants determined and plants classified followed after Raunkiaer [33] and Mueller-Dombois, & Ellenberg [34].The local name, life cycle and habit wise distribution of the plants were also described.The collected specimens were identified with the help of various floras, illustrations & monographs [35][36][37][38][39][40][41][42][43][44][45].The voucher specimens were deposited in the herbarium of Cholistan Institute of Desert Studies, The Islamia University of Bahawalpur.

Results and Discussion
The present study examines the flora of the Cholistan desert, which indicates that the flora of the Cholistan desert belongs to 154 plant species of 106 genera and 38 families.Among the existing families, 33 families are dicotyledons, 4 families of monocotyledons and 1 family of gymnosperms (Table 1   The habits of the plant species found as, 75 species (49%) were herbs, 34 species (22%) were grasses, 21 species (14%) were shrubs, 10 species (6%) were trees, and 9 species (6%) were subshrubs, 2 species (1%) were sedges and 3 species (2%) were climbers (Figure 3).The life span or life cycle distribution of the plant species in the study area were represented by 79 species (51%) perennials and 75 (49%) annual species (Figure 4).

Figure 1 .
Figure 1.Location map of the Cholistan desert.

Figure 4 .
Figure 4. Graphical respresntastion of life cycle of plant species of Cholistan desert.

Table 1 . List of plant species of Cholistan desert.
).The largest family of the area is Poaceae with 34 species.Papailionaceae and Zygophyllaceae are with 10 species.Asteraceae is present with 9 species.Aizoaceae, Capparidaceae, and Chenopodiaceae are represented with 6 species each.Asclepiadaceae, Amaranthaceae and Solanaceae are represented with 5 species.The families with 4 species are Boraginaceae, Convolvulaceae, Cucurbitaceae, Euphorbiaceae and Mimosaceae.Brassicaceae, Cyperaceae, Molluginaceae, Nyctaginaceae, Polygonaceae and Rhamnaceae have 3 species each.Malvaceae, Portulaceae, Tamaricaceae and Tiliaceae are represented by 2 species.The rest of thirteen families are represented with one species.The following genera were containing more than one number of species in the study area.The Genus Cenchres nd Eragrostis were with 4 species.Aristida, Boerhavia, a