The Kingdom of Saudi Arabia shares its flora with the east African countries and the Afro-montane region in the west, the Mediterranean and Irano-Turanian region in the north and north east, eastern Iran, Pakistan and India in the south-east, and southern Arabia including Socotra in the south. In addition, the Kingdom has its own endemic species. Knowledge about the plants of Saudi Arabia and their uses is ancient. But like other ancient knowledge of plants in many other countries, it has remained ancient

The Kingdom extends from 32° 12' N latitude on the Jordanian border in the north to 16° 00' N at the Yemeni border in the south. It is bounded by the Red Sea in the west and the Arabian Gulf in the east.

Western Saudi Arabia is dominated by a mountain chain running the entire length of the country, known as the Hejaz and Asir mountains. It runs parallel to the Red sea and rises to between 1300 - 3000 m. above the Tihamah coastal plain to its west. The flat coastal plain along the edge of the Red sea is hot and humid with temperature reaching 45° C in the shade during the summer months, with 90% relative humidity. The winter is considerably cooler but due to the relative warmth of the sea, it is never cold. From this fertile crest it falls towards the east as a desert plateau to the dry interior or the Najd containing the Dahna and Nafud which extends to the great sand desert of the Rub Al Khali (The Empty Quarter). From the Dahna dunes to the east coast the terrain alternate between rocky outcrops and gravel plains. The eastern region lies on the Arabian Gulf coast and contains salt flats (sabkhahs). There are many artesian wells along the coast which are used to irrigate large areas under cultivation around Hofuf and Qatif.

Saudi Arabia divides naturally into seven terrestrial physiographic regions (with 30 sub-regions) and two marine regions (Child and Grainger 1990)

1. The Tihamah
2. Western Highlands
3. Arabian Hinterland
4. The Cuesta region (Sedimentary Najd)
5. Aeolian Sands: an-Nafud, Ad-Dahna, Al-Jafurah, Ar-Rub' al-Khali
6. As-Summan and Widyan Plateaus
7. Arabian Gulf coastal region
8. The Red Sea
9. The Arabian Gulf