Very little information about plant use in Africa has been written down. In African thought, all living things are believed to be connected to each other, to the gods, and to ancestral spirits. If harmony exists between all of these, then good health is enjoyed, but if not, misfortune or ill health will result. Forces can be directed at humans by displeased gods, ancestors, and witches, resulting in disharmony which must be resolved before good health can be restored. Treatment may also involve much more than medicine. Practices such as divination and incantation maybe carried out to help with diagnosis, and sacrifices may need to be made in order to placate the supernatural entity.
The traditional healer is also likely to be a religious leader, since health and spirituality are closely intertwined in Africa. Traditional healers have existed throughout Africa since prehistoric times, for example, the ifas and juju men of West Africa or the inyanga (sangoma is the term used for diviners) of South Africa. Various methods have been used to identify “healing plants,” such as trying to find a plant that possesses a stronger spirit than the one causing the disease, or by using the “law of signatures.” This system existed in other parts of the world, including Europe in the Middle Ages (Grier 1937), and is based upon the concept that nature has provided a cure for every disease. Matching a plant to a disease for a cure involves finding a plant with a similar form to the diseased organ. For example, plants with a red flower would be used in blood disorders, and yellow-flowered plants in cases of jaundice.
The use of medicinal plants in Africa also provides the observer with timely reminders of how sustainable cultivation can protect a resource (Aloe ferox, Southern Africa), but a species may likewise move toward regional extinction through over-exploitation (Prunus africana, Cameroon).
African devil’s claw, Grapple plant Harpagophyturn procumbens / Pedaliaceae
Devil’s claw or grapple plant derives its name from the formidable “claw,” the dried hooked thorns of the fruit used in seed dispersal, which are a hazard to any passing cloven-hoofed animal or careless human. The plant is native to southern and eastern Africa and it is collected in regions bordering the Kalahari Desert. It thrives in clay or sandy soils and is often found in parts of the South African veldt. The tubers are traditionally used as a tonic, for “illnesses of the blood,” fever, problems during pregnancy, and kidney and bladder ailments. Since the mid-1980s and with considerable research effort, African devil’s claw has been developed into a very successful and relatively well-characterized phytomedicine for the treatment of pain relief in joint diseases, back pain, and headache. Most pharmacological and clinical research has been conducted on standardized extracts. The secondary storage tubers are collected and, while they are still fresh, they are cut into small pieces and dried. The main exporters are South Africa and Namibia. Attempts are currently under way to cultivate the species because over-harvesting has led to conservation concerns.
The dried and powdered root of the plant is now included in the European Pharmacopoeia (2002) and some national pharmacopoeias, such as that of Switzerland. Several constituents are known, including iridoids and phenylethanoids, but the active constituents have not been identified with certainly.
Aloe Aloe vera / Aloeceae
Aloe vera (also known as A. barbadensis) has long been used because of its medicinal properties and its mythical significance. Depictions of a plant similar to A. vera appear in wall carvings and paintings in ancient Egypt (2000 bc), but its use prior to the Roman period is speculative. Alexander the Great learned of aloe after conquering Egypt in 332 bc and, on Aristotle’s advice, had his army capture the island of Socotra where Aloe grew, thus ensuring that his soldiers, rather than the opposition, would benefit from the healing powers of this plant. The first-century Greek herbal of Dioscorides gives a description of the healing powers of aloe and noted it was the sap, and not the gel, that was the healing agent. It should be clearly stated here that confusion does exist about which component of aloe is to be used. The gel, from the parenchyma cells in the inner leaf pulp, is the part that has been used medicinally for centuries and should be clearly distinguished from the exudates (or latex). This latex originates from the bundle sheath cells just beneath the outer skin of the leaves, is characterized by its yellow color and bitter taste, and is used as a strong purgative.
The plant is native to Africa. Its former scientific name, A. barbadensis (from the Caribbean island of Barbados), originates from the time lesuit priests exported the plant from South America to Spanish territories in the Caribbean (lamaica and Barbados) and subsequently imported it to England in the 17th century. Aloe ferox, or Cape aloe, is native to southern Africa and is widely applied in phytotherapeutic preparations. Aloe extracts incorporated into over-the-counter cosmetic and medicinal products are now widespread throughout the world. Aloe gel is used widely in many preparations including those for wound treatment, especially burn wounds and inflammation, as extensively reviewed by Reynolds and Dweck (1999) and Reynolds (2004). All Aloe species are protected by the Convention on International Trade in Endangered Species (CITES).
Cola nut, Sudan cola nut Cola acuminata and C. nitida / Sterculiaceae
These two taxa of evergreen trees are sometimes considered to be one species. They are endemic to the lowland forests of western Africa, especially Sierra Leone, Liberia, Ivory Coast, and Ghana, and have been introduced to Nigeria, Mali, and Guinea. Cola nitida is widely cultivated in the Caribbean. The medicinally used part of the plant is the cola nut (the tree’s seed kernel) which is chewed to produce saliva. The seeds are rich in caffeine and related alkaloids and have consequently been used as a stimulant. However, cola’s importance in African traditional societies goes beyond this: it is a symbol of friendship, and guests receive a cola nut on arriving at a house. Also many ceremonies are ended by jointly eating cola nuts. The first drawing of a cola nut was published by Clusius in 1591, but it was only in the 19th century that the nut became more widely known in Europe and North America. Travelers’ stories of using it to ease the hardship of expeditions and travel highlighted the stimulating effects of C. nitida, but it has no modern biomedical use.
Myrrh Commiphora myrrha / Burseraceae
Myrrh is indigenous to Northeast Africa, particularly Somalia and Ethiopia, and is one of the oldest and most highly esteemed botanical drugs. The drug used is the gum resin (an exudate), which is excreted by the trees through the bark. In present-day Morocco, for example, it is used as a balsam and for nervous disorders, and it is applied in cleansing ceremonies such as ritual fumigations. In vivo anti-inflammatory effects have been reported for its extract.
Red stinkwood Prunus Africana / Rosaceae
The bark of Prunus africana is obtained from a tree that grows in the high (at elevations of 1000-2500 m) mountain forests of Africa and Madagascar). It has been developed into a phytomedicine and used to treat benign prostate enlargement, with good clinical evidence pointing to the extract’s efficacy. Within Africa, different decoctions of the plant are used to treat various conditions, including fevers, urinary tract infections, and inflammation (bark tea), and to prepare wound dressings (leaves), and the leaf sap is drunk for insanity. In the regions of origin a high-quality extract is produced from the botanical drug, which is mostly exported to Italy, France, and Spain. This extract could provide a sustainable and valuable income for many of the African countries, especially for Cameroon and Madagascar. However, the bark is currently harvested from this slow-growing tree in an unsustainable manner. Overharvesting has resulted in serious damage to plant populations and it is now CITES-listed. Consequently, there has been a drive to stop the collection of the bark or, alternatively, to increase efforts to cultivate the species. These have been hampered by shortage of seed stocks and the long unproductive period as the tree matures.
Rosy periwinkle Catharanthus roseus / Apocynaceae
A small, erect shrub, the rosy periwinkle (Madagascar periwinkle) is native to Madagascar but can now be found as a widely cultivated plant in warm climates around the world. The plant reaches a height of 3 feet (1 m) and has smooth oblong leaves; the pink or white flowers are borne all year round on the upper leaf axils. The plant is used in South Africa to treat diabetes and rheumatism, but its pervasive growth has now caused it to become a weed, especially in Kwa-Zulu Natal and Mpumalanga.
In Madagascar the plant is widespread, reflecting its multiple uses in herbal treatments. The striking floral display of the plant has promoted its spread around the world and has led to variations in its medicinal applications. By the early 20th century it was being used as an oral hypoglycemic agent (to lower blood sugar levels) in South Africa, southern Europe, and the Philippines; to treat diabetic ulcers in the West Indies; and to control hemorrhages and scurvy in Brazil. The role of the plant as an antidiabetic agent in the Caribbean led to the discovery of its effective anticancer activity. Diabetics in Madagascar were taking a periwinkle tea in preference to the more expensive insulin treatments. This prompted a small scientific study which found that rats given the tea had a significantly lowered white blood cell count. Although fatal to the rats, this finding prompted the researchers to investigate the effect of the Madagascar periwinkle against leukaemia, a disease caused by an abnormal increase in white blood cells. The active agent was identified as a new alkaloidal compound termed vinblastine which was licensed in the United States and approved for use in cancer treatments in 1961. A related alkaloid from the same plant, vincristine, was licensed as a drug two years later. Rosy periwinkle is now widely grown for extraction of these alkaloids.