Leaf characteristics of the African olive (Cuneo and Leishman, 2006).
Background: Medicinal plants have been used as a key source for medication and they remain to provide new therapeutic remedies to date. Extracts of Olea europaea subsp. africana Oleaceae (leaf, bark and root) are used extensively in Africa to treat various diseases traditionally. Phytochemistry has identified phenols, terpenoids and coumarins in different parts of the plant. However, little pharmacological studies have been done on Olea europaea subsp. africana. The present review aims to compile available information on the ethnobotany, phytochemistry, pharmacology and toxicology of Olea africana.
- Olea europaea subsp. africana
Medicinal plants are defined as any plant containing substances which can be used for curative purposes in one or more parts of its organ, which are precursors for the production of useful drugs [1, 2]. A vast number of these plant species have been used in treating numerous ailments for decades [3, 4]. In Africa, the use of traditional medicine dates back 4000 years ago before the use of orthodox medicine . According to the World Health Organization, traditional medicine still remains the primary healthcare system for an estimated 80% of the population in Africa, because of its affordability and accessibility [2, 6]. South Africa has a profound native knowledge on plants used as traditional remedies . An estimated 30,000 species of higher plants are found in South Africa and 3000 of these species have been used in phytomedicine across the country . It is approximated that 3 million of the South African population uses phytomedicine for primary health purposes [5, 7].
Plant fragments such as leaves, bark, roots, flowers and seeds can be used to derive traditional remedies . These can be prepared not only from a single plant but a combination of plant concoctions , aiding in ailments such as influenza, arthritis, heart burn, kidney infections, high blood pressure, etc. . Traditional medicine has also contributed to the management of epidemic diseases such as HIV/AIDS , malaria  and diabetes . The therapeutic potential of medicinal plants is due to the existence of phytochemicals which comprise of tannins, alkaloids, flavonoids, essential oils and chemical compounds established as subordinate metabolites in plants . It has been reported that at least 25% of commercial drugs are derivatives from plants , such as picrotoxin and aspirin , and various others are analogues made by chemical synthesis fabricated from isolated compounds from plants . However, biomedical literature data are miniature regarding the safety, quality and efficacy of the plants used in traditional medicine . Therefore, there has been a sudden growth in the interest of studying and using medicinal plants which have led to the isolation of active chemical compounds for therapeutic significance . The plant species from the family
The olive shrub is rarely consumed as a natural fruit due to its bitter taste but used as oil or table olive [16, 22], and its wild and cultivated forms are considered as a significant botanical research subject . The traditional use of leaves includes treatment for fever, malaria, bacterial infections, diabetes, inflammatory disorders and hypertension . The decoction of leaves is also used as a mouthwash to treat aphthous, gingivitis and glossitis . The preparation of the bark concoction is taken to treat tapeworm infestation . Olive oil is used externally in the treatment of insect stings and burns . Previous studies established that olive leaves have antioxidant, anti-inflammatory , anticancer, antihypertensive and antidiabetic properties . These activities have been shown to be displayed by compounds isolated from the olive tree including iridoids, secoiridoids, lignans, biophenols, flavonoids, flavone glycosides, isochromans and terpenoids [16, 19]. Six species of the olive tree are currently recognized: subsp.
Olea europaea subsp. africana
The African species of
2.1.1. Geographical distribution
2.1.2. Botanical description
The wild olive tree is a shrub which grows to 5–10 m in height, irregularly reaching 18 m . The trees mature into a wild, rounded pattern with a solid upper layer and twisted trunk when exposed to dry conditions . The bark is grey to brownish and flaky once it matures . Flowers are greenish white in colour, 6–10 mm long, with a sweet aroma and held insecurely in axillary or occasionally terminal heads [15, 26]. The ovoid fruit are thinly fleshy, about 7–10 mm in dimension, and upon maturation it turns black or dark brown  (Figures 2–6; Table 1).
|Taxon||Leaf characteristics||Field characteristics/comments|
|African wild olive
Phytochemicals are various biologically active compounds that occur naturally in plants, which provide potential medicinal benefits for humans . These chemicals assemble in several parts of the plant including the flower, stems, seed, roots and leaves . Phytochemical screening of the African wild olive has led to the separation of phenolic compounds, known as oleuropein, tyrosol and hydroxytyrosol  flavonoids , triterpenoids (oleanolic acid, ursolic acid)  (erythrodiol and uvaol)  and coumarin glucosides (esculin and scopolin) .
Plant phenols are aromatic secondary metabolites, containing antioxidant and antimicrobial properties . The compound oleuropein is a coumarin-like compound, which is profuse in the family
Triterpenoids are a vastly varied group of natural products, including steroids, extensively dispersed in plants . These compounds are accumulated by plants in their glycosylated form (saponin) . Oleanolic acid (Figure 8) is a biologically active pentacyclic triterpenoid with pharmacologic activities, such as anticancer, hepatoprotective effects, antioxidant and anti-inflammatory . Oleanolic acid is often in existent with its isomer ursolic acid (Figure 9) . Ursolic acid is biologically used as an antioxidant, anticancer and anti-inflammatory chemical . Erythrodiol and uvaol are triterpenoids belonging to the oleanane and ursane classes . These compounds have been stated to possess antimalarial, antifungal, antileishmanial, antibacterial and anti-inflammatory activities . Triterpenoids isolated from
Coumarins are derived from 1,2-benzopyrones, containing of a large class of phenolic elements originating in plants [38, 39] and distributed in the following families:
2.1.4. Medicinal uses
The wild olive tree has been stated to be “the most important plant” from 120 plants being used in traditional medicine .
22.214.171.124. Antidiarrhoeal activity
A study by Amabeoku and Bamuamba  investigated the methanolic leaf extract of
126.96.36.199. Antihypertensive, antiatherosclerotic, hypoglycaemic and antioxidant activity
Somova et al.  stated that the African wild olive leaf can prevent atherosclerosis and hypertension and improve insulin resistance. The experimental animals were treated at a dosage of 60 mg/kg b.w with ethyl acetate leaf extract, as this fraction is known to contain the active compound oleuafricein. Hemodynamic screening was evaluated for 42 days monitoring the administration of the drug, heart rate, systolic and diastolic blood pressure. The Lipschitz test was conducted to record the excreted urine after 5 h and after 24 h. On completion of the study, the animals were starved overnight and killed. Following killing, blood glucose was estimated, and glutathione peroxidase and superoxide dismutase were assayed. These biochemical parameters showed that treatment with
A study by Abdel-Sattar et al.  reported antihypertensive, hypoglycaemic and antioxidant properties of
188.8.131.52. Antibacterial activity
A study by Douglas et al.  evaluated the antibacterial activity of the leaves of
A study by Douglas and Jeruto  investigated antibacterial activity of
Amabeoku and Bamuamba  examined
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