The most important topographic and floristic diversity of Saudi Arabia can be seen in the mountainous North and South Hijaz regions, stretching parallel to the Red Sea coast. Various scientists and explorers have carried out several studies during the past few decades to explore the vegetation of these regions. The mountains of south western region are more or less continuous with peaks reach elevations of over 2000 m in the vicinity of Taif and over 3000 m southwards, towards Abha. The stony mountains in the north-western region, on the other hand, are generally discontinuous with peaks reach between 1500-2800 m.  Isolated mountains in north central Saudi Arabia and an arch like Jabal Tuwaiq, extending the entire central region are less elevated, ranging between 1000-1500 m. Unlike the vegetation of northern and southern Hijaz Mountains, the vegetation in other parts of the country including that of sand seas and range lands in the central and northern region is less important in terms species diversity.

 The vegetation of Raida escarpments (1500-2800 m), previously an inaccessible one due to the region's steep slopes, is now facing degradation because of increased pastoral activity. Though this escarpment is protected and containing a large number of trees including Juniper forests in pristine conditions, the populations of a moderate number of species, including some of the rare species such as Huernia saudi-arabica, Ceropegia spp., Scadoxus multiflorus, Klenia odora, Adenia venenata etc., are increasingly marginalized during the past few years. All these threatened populations do not have more than 50 plants/10 sq. km.

                                 Mountains in the Fayfa region, close to Yemen borders, and other isolated mountains like Jabal Abu-Hassan also harbor a diverse flora, which is more or less similar to that of East African, one. A considerable number of endemics have also been reported from these regions. Fayfa Mountains (2000 m) which receive a constant moisture-laden breeze on the west facing slopes support the life of many endangered species including few remaining stands of Dracaena ombet, Dorsetnia foetida, Ceropegia spp., Rhytidocaulon spp., etc. Though the mountains in the Saudi-Yemen border do not have any remarkable variation in terms of precipitation and temperature, the density and variation in the vegetation of Yemen are apparently higher than that of the Fayfa Mountains. This is perhaps due to the increased urbanization practices or the effect of centuries-old terraced cultivation on virgin lands. A considerable number of species recorded from the northern mountains of Yemen have so far not been collected from Fayfa Region. The ways to trace those species, which were disappeared from these mountains (local extinction), are virtually, nil, as all previous literature covering this part of the region did not mention any exact collection detail or all collections are from within the borders of Yemen only.

Vegetation in the semi-arid mountains of Jabal Shamanseel (1600 m), Jabal Radhwa (2000 m), Jabal Sha'ar (2350 m) had been studied by Chaudhary et al., 1988). The gullies and slopes of these mountains support a range of wild plants, dominated by Juniperus phoenicea, Delonix elata, Ferula ovina, Pistacia khinjuk, Launaea acanthodes, Commiphora spp. Most of these plants' populations are reported to be in a critical state due to increased human activities and the poor regeneration by themselves. One of the rare species, Astragalus fruticosus is also reported from the highest elevations of Jabal Sha'ar as an occasional plant. Jabal Lawz (2800 m), the highest mountain in the northern Hijaz also possesses varied vegetation with a strong Mediterrannean influence. Prunus korshinskyi, one of the dominant and high altitude members, is the star attraction of this mountain. It is represented by few plants, and can not be seen anywhere else in the country. In addition to this, the Jabal Sha’ar also houses a number of rare species such as Androssace maxima, Plantago maris-mourtii, Tanacetum santolinoides, Scandix pecten-veneris etc.

                                                     Plant Diversity Hot-Spots of Saudi Arabia

Al-Aridah

Al-Bala

Al-Fiqrah

Al-Wajh Bank

At-Ta’if

Ballasmar

Farasan Islands

Hakimah

Harrat al-Harrah

Hisma

Ibex Reserve

Jabal Abu Hassan

Jabal ad-Dubbagh

Jabal Aja

Jabal al-Lawz

Jabal al-Qahar

Jabal as-Sudah

Jabal Batharah

Jabal Fayfa

Jabal Hashar

Jabal Jandaf

Jabal Radwa

Jabal Salma

Jabal Sha'ar                                      

Jabal Shada

Jabal Shamanseel                             

Jabal Tallan

Jabal Uthrub

Jabal Wirqan

Jazirat Sharifah

Jibal as-Samrah

Jibal Qaraqir

Majami‘ al-Hadb

Muhayil

Murtafa‘at Najran

Ra’s Kishran

Raudat Khuraim       

Raydah

Suq al-Ithnayn (Tamniyah)

Tanumah

Uruq Bani Ma‘arid

Wadi al-Hizmah / Wadi Tathlith

Wadi Ghaythan

Wadi Jawrah

Wadi Lejib

Wadi Maraba

Wadi Sadr

Wadi Tarj

Wadi Tayyah