Wadi Nissah is located about 50 km south of Riyadh City. It lies between 46 ° and 47 ° E and 24 ° 30’N and 24 ° 00’N. It is relatively a large basin, bordered on the northern side by Wadi Hanifah and on the southern side by Wadi Al-Hawtah and Wadi Al-Ayn. The drainage basin area is about 1800 km2 that covers the catchment area of Wadi Nisah and Wadi Awsat. Western side is bordered by the Tuwaiq Mountains and the eastern side is bordered by Al-Kharj town. The Wadi Nissah and its tributaries are covered by alluvium and sand dunes and are bordered on the north and south by hillocks ranging in height from 100 to 200 feet. Vegetation of the wadi is somewhat sparse, mainly dominated by Acacia raddiana, A. ehrenbergiana, Calotropis procers, Rhazya stricta and Senna italica
Acanthaceae
Blepharis ciliaris
Aizoaceae
Aizoon canariense
Amaranthaceae
Aerva javanica
Apocynaceae
Rhazya stricta
Asclepiadaceae
Calotropis procera
Glossonema variens
Leptadenua pyrotechnica
Pergularia tomentosa
Asphodelaceae
Asphodelus refractus
Asphodelus tenuifolius
Boraginaceae
Arnebia decumbens
Arnebia hispidissima
Heliotropium bacciferum
Heliotropium digynum
Moltkiopsis ciliata
Trichodesma africanum
Capparaceae
Capparis spinosa
Cleome amblyocarpa
Cleome rupicola
Dipterygium glaucum
Maerua crassifolia
Caryophyllaceae
Gymnocarpos decander
Gypsophila capillaris
Herniaria hirsuta
Paronychia arabica
Paronychia robbiaria
Polycarpaea repens
Pteranthus dichotomus
Silene arabicus
Silene linearis
Silene villosa
Chenopodiaceae
Bassia eriophora
Bassia muricata
Chenopodium murale
Haloxylon salicornicum
Salsola imbricata
Cistaceae
Helianthemum lippii
Compositae
Anthemis deserti
Anvillea garcinii
Artemisia monosperma
Artemisia scoparia
Atractylis arabicus
Centaurea pseudosinaica
Echinops erinaceus
Filago desertorum
Ifloga spicata
Koelpinia linearis
Lactuca saligna
Launaea capitata
Launaea mucronata
Picris babylonica
Pulicaria glutinosa
Pulicaria undulata
Rhanterium epapposum
Scorzonera musillii
Senecio glaucus
Sonchus oleraceus
Tripleurospermum auriculatum
Zoegea purpurea
Convolvulaceae
Convolvulus austro-aegyptiacus
Convolvulus buschiricus
Convolvulus glomeratus
Convolvulus oxyphyllus ssp. oxycladus
Convolvulus pilosellifolius
Seddera latifolia
Cruciferae
Anastatica heirochuntica
Cakile arabica
Diplotaxis harra
Eremobium lineare
Farsetia stylosa
Morettia parviflora
Savignya parviflora
Schimpera arabica
Zilla spinosa
Cucurbitaceae
Citrullus colocynthis
Cucumis prophetarum
Cyperaceae
Cyperus conglomeratus
Ephedraceae
Ephedra foliata
Euphorbiaceae
Chrozophora tinctoria
Euphorbia granulata
Euphorbia retusa
Ricinus communis
Geraniaceae
Erodium laciniatum
Monsonia nivea
Gramineae
Andropogon distachyos
Aristida adscensionis
Avena fatua
Cenchrus ciliaris
Centropodia forsskalii
Centropodia fragilis
Chrysopogon plumulosus
Cutandia memphitica
Cynodon dactylon
Eragrostis barrelieri
Hyparrhenia hirta
Ochthochloa compressa
Panicum turgidum
Pennisetum divisum
Schismus barbatus
Stipa capensis
Stipagrostis drarii
Stipagrostis plumosa
Tetrapogon villosus
Labiatae
Salvia deserti
Teucrium oliverianum
Teucrium polium
Leguminosae
Acacia ehrenbergiana
Acacia gerrardii
Acacia oerfota
Acacia raddiana
Astragalus haurensis
Astragalus spinosa
Medicago laciniata
Senna italica
Taverniaria aegyptiaca
Tephrosia purpurea
Trigonella hamosa
Trigonella stellata
Malvaceae
Malva parviflora
Molluginaceae
Gisekia pharnaceoides
Neuradaceae
Neurada procumbens
Orobanchaceae
Cistanche tubulosa
Plantaginaceae
Plantago amplexicaulis
Plantago boissieri
Plantago ciliata
Plantago ovata
Polygonaceae
Calligonum comosum
Emex spinosa
Rumex vesicarius
Resedaceae
Ochradenus baccatus
Reseda arabica
Rhamnaceae
Ziziphus nummularia
Rubiaceae
Kohautia caespitosa
Pterogaillonia calycoptera
Rutaceae
Haplophyllum tuberculatum
Scrophulariaceae
Sclerocephalus arabicus
Scrophularia deserti
Solanaceae
Lycium shawii
Tiliaceae
Corchorus depressus
Umbelliferae
Anisosciadium lanatum
Zygophyllaceae
Fagonia bruguieri
Fagonia glutinosa
Fagonia indica
Seetzenia lanata
Tetraena propinqua
Tribulus inermis
Tribulus macropterus
Tribulus terrestris
