SA is the largest country in the Arabian Peninsula, occupying about 2.25 million km², or nearly 80% of the peninsula [21]. Forests cover about 27,000 km² of its total area, mostly in the southwestern part of the Kingdom [22], while the area of natural rangeland exceeds 1.75 million km² [23]. Plant diversity plays a key role in maintaining and preserving ecological balance and stability, which is an important factor for human well-being, not only for the country but for the whole world [24]. In recent years, a significant amount of data have been published about the flora in SA, which revealed that the country is gifted with a wide variety of plants, including a large number of herbs, shrubs, and trees that are found in desert, semi-desert, and mountainous ecosystems [25,26,27]. Geographic and climatic diversity, changes in water resources, drought, and anthropogenic pressures, such as overgrazing, deforestation, and all developmental activities in SA, negatively affect biodiversity, impacting the structure of the flora and natural vegetation [22,28]. The climate of SA varies greatly depending on the area and the season; it is characterised by extremes in weather, with very high temperatures during the daytime followed by an abrupt drop in temperature at night and very little, irregular precipitation (i.e., a typical ‘desert climate’) [21]. The annual mean temperature of the country is 24.64 °C, with Turaif in the north recording the lowest temperature (19.10 °C) and Makkah in the west recording the highest temperature (31.69 °C), with an average of 17.62 °C, exhibiting an increasing gradient from north to south [29]. Rainfall and temperature are considered the key controllers of agricultural production [30]. The annual average rainfall in SA from 1979 to 2009 was 93.5 mm, and it is expected that by 2050, some parts of SA will experience a decrease in rainfall by 20–25% in dry seasons and 10–15% in the winter. The maximum temperature has increased significantly, especially in dry seasons, by 0.72 °C per decade [31].

SA is home to about 2247 plant species, including native and introduced plants that belong to 142 families and 837 genera, and the components of its flora are the admixture of the features of Africa, Asia, and the Mediterranean region in addition to a large number of about 246 endemic species [32,33,34,35,36]. Of them, about 105 species reside in dunes, 90 species are halophytes, 75 species are trees, and aquatic plants comprise 12 species. About 450 species of total flora have a direct benefit to humans; 334 species have medicinal value, 38 species are palatable fodder, 25 species are human food, 45 species are poisonous, 47 species are used as ornamentals, and 471 species are used in ethnomedicine [22,37]. Of note, about 600 species of plants in SA are rare and endangered in their habitat [38].

Mecca city district is characterised by various types of plants; it was reported that a total number of 184 species of 125 genera and 44 families are found in Mecca. The most well-known families are Poaceae (17%), Fabaceae (13%), and Amaranthaceae (5%) [32]. Moreover, wadis represent one of the most notable desert landforms where physiographic irregularities appear, leading to parallel variation in species distribution and life forms. In wadi Al-Noman in Mecca, about 126 species from 39 families have been recorded, namely Fabaceae, Poaceae, and Boraginaceae. The authors indicated that species diversity in the studied area may be positively associated with the high pH and mineral content of the soil [39]. The vegetation along a transect between Makkah Al-Mukarramah and Al-Madinah Al-Munawarah in the Hejaz Mountains includes 106 species of vascular plants from 35 families [40]. In a survey of a sector in the Hejaz mountains along the Medina-Badr road, 247 species of 173 genera and 52 families are listed [41]. In Jizan province in the southern region, with varied landscapes such as wadis, islands, plateaus, and mountains, 850 species of 434 genera from 98 families represent about 37% of all the species in SA. Of them, 536 species are from Jabal Fayfa and 202 species are from the Farasan Islands. The most dominant families are Poaceae, Papilionaceae, and Asteraceae, with a total of 87, 70, and 60 species, respectively [42]. In a survey of the flora of the Sarwat Mountains in Taif as showed in Figure 1, 261 species from 178 genera and 55 families were recorded, of which Asteraceae, Poaceae, Fabaceae, Lamiaceae, Chenopodiaceae, Boraginaceae, Asclepiadaceae, Brassicaceae, and Zygophyllaceae were the most common [43]. In another mountainous area, the Asir mountains in the southwest of SA, 189 species of 74 families were recorded; Asteraceae was the dominating family in the study area (36.5%) followed by hemicryptophytes (15%) and geophytes (12.5%) [28]. In the eastern part of the Kingdom, no more than 370 native species of herbs and shrubs are adapted to the desert climate, reflecting the difficulties faced by plants in these harsh environments; the same applies for the northern part [44]. This is in contrast with Asir Hijaz, the western mountainous area of the Kingdom, which has large species diversity due to the greater rainfall [33]. The number of recorded species is still increasing through new biodiversity surveys [32]; however, the richness and diversity of the flora might be lost due to anthropogenic pressure and changes in climate [37,45]. Therefore, further studies are needed to ecologically and taxonomically evaluate all the flora of the country and to provide suitable conservation measures for these valuable species with unique features.

People have used plants to meet their various needs throughout different eras. Plants have formed the basis of traditional medicine for at least 6000 years in Mesopotamia and Egypt, with Hippocrates serving as a landmark for the written traditions on medicines [46,47]. Traditional medicine has been and is still a part of the culture of SA [48]. SA has some unique features besides its religious position. Zamzam Well is one of the most well-known places in SA, known for its suitable environment for many herbs and shrubs, as mentioned in the verses of the Qur’ân: Our lord, I have settled some of my offspring in a barren valley, near your sacred House, our Lord, that they may establish prayer. So make the hearts of people incline towards them and provide them with sustenance that they may give thanks (Verse # 37, Surah Ibrahim, p. 260).

Agriculture has been the main source of economic income for several Saudi regions, even during the pre-Islamic times, and farmers followed both advanced and traditional irrigation methods by diverting rainwater flowing into agricultural terraces or bringing rainwater drawn from dams to irrigate parched wadis [43]. From the 7th century, SA has been the historical origin of Islam. ‘Traditional Islamic medicine’ is the term used to describe medical traditions thriving during Islam’s golden age [49]. In fact, many plants are highly recommended by Prophet Muhammad (peace be upon him (PBUH)). Other plants are mentioned in different surahs of the Holy Qur’ân, such as date palm, olive, toothbrush tree, camphor tree, squash, ginger, onion, grapes, clover [50]. Prophet Muhammad (PBUH) mentioned the use of Miswak (Salvadora persica L.) for oral hygiene [51]. The Prophet (PBUH) said, ‘Siwak (Miswak) is a means of purification for the mouth and is pleasing to the Lord’ [52]. At that time, the use of medicinal plants to prevent and treat health disorders flourished, and philosophers and physicians, such as Al-Razi and Ibn Sina, began to change the concept of medicine. They compiled medical books from the knowledge available in the Mediterranean region (e.g., from Egyptian, Persian, Greek, and Roman times) that have been used for centuries (700–1500 AD). This knowledge was selected through controlled experimentation and sound reasoning. ‘The Canon of Medicine’, ‘The Book of Healing’, and ‘Kitab Al-Hawi’ are the most famous books written by Ibn Sina (Father of Early Modern Medicine) and Al-Razi [50,53].

For these reasons, people in SA have taken an interest in plants; about 80% of Saudi citizens have used medicinal plants for their primary health care [11]. Recent publications reported the activity of S. persica (Miswak, toothbrush tree) against oral bacteria that cause caries. This species showed effective antimicrobial, antiulcer, analgesic, anti-inflammatory, and antitumour activities, which agrees with the recommendations of the Prophet (PBUH) [54]. The uses of 12 medicinal plants that were recommended by the Prophet (PBUH) and mentioned in Qur’ânic verses were recently published [50,55].

4. Anti-Inflammatory Activity of Saudi Arabian Plants