Medicinal plants used in traditional medicine by Oromo people, Ghimbi District, Southwest Ethiopia

About 85% of world population uses herbal medicines for prevention and treatment of diseases, and the demand is increasing in developed and developing countries [1]. Some 25% of drugs contain compounds obtained from higher plants [2]. Moreover, the investigation of herbal drugs from plants to treat AIDS, cancer, and malaria, chronic complaints such as rheumatism, arthritis and asthma have been reported [3‐5]. Herbal remedies are enjoying widespread popularity throughout the world [6, 7]. However, only 10% of medicinal plant species is cultivated today while the larger majority being left under wild stands threat [8, 9].

Ethiopia is endowed with a diverse biological resources including about 6, 500 species of higher plants, with approximately 12% endemic, hence making it one of the six plant biodiversity rich regions [10]. Of these, more than 62.5% of the forest area are found in southwest region of Ethiopia [11] where most of the medicinal plants are confined [12] and have been used as a source of traditional medicine to treat different human and livestock ailments [13, 14]. Use and management of many medicinal plants in Ghimbi district has been reported by [15]. However, this former study does not provide sufficiently detailed information on the status of Traditional Botanical Knowledge (TBK) transfer from generation to generation based on Oromo Gada system age groups and educational levels as wells as on the ranking of most potential medicinal plants for specific disease treatment in the study area. The present study was therefore to identify those potential and popular medicinal plant species used for the treatment of various diseases in Ghimbi area by Oromo community.

This study revealed 49 medicinal plant species representing 31 families and 43 genera used to treat various human ailments. Of these, 13 species were in common with [21], 14 with [13], 15 with [22]. Three species that are common with [23] are known to be used in the medicinal flora of other African countries. In this study, Family Fabaceae was represented by 5 species followed by 4 species of Asteraceae, and Lamiaceae each and 3 species of Euphorbiaceae. Fabaceae, Asteraceae, and Lamiaceae are among the most represented families in the flora of Ethiopia and Eretria ([24‐26]. This study shows that the highest percentage of medicinal plants was obtained from wild while the rest were from home garden. In agreement with this study, similar percentage of medicinal plant species reported from different parts of the country by [23, 27‐29]) were from natural vegetation.

Analysis of growth habit of medicinal plants in this study indicated that there was no such difference especially in the proportion of herbs and trees. The distribution of similar proportion of growth forms is an indication of the harmonious growth of indigenous forest species different from the arid and semiarid regions reported by various authors [6‐33].

Analysis of data on plant parts used indicated that leaf is the major part widely employed by local healers in the preparation of remedies followed by root. Previous reports in Ethiopia [15‐22, 24‐26, 30‐33]. have also shown that leaves were the most commonly used to treat various health problems Given the highest frequency of leaves used for medicinal purposes in the study area threat to the destruction of medicinal plants especially to trees and shrubs was found to be minimal, as high threat to the mother plant comes with root, bark and leafy-stem harvests. However, [34] indicated that the harvest of leaves has also a threat to the deterioration of medicinal plants since the removal of leaves limits the transformation of vegetative to reproductive development sucha as flower production and fruit/seed set, which in its turn limits the natural/wild regeneration of plants.

The dependency of local people on fresh materials in the study area including the removal of fresh barks and leaves put the plants under serious threat than the dried form, as fresh materials are harvested directly and used soon with its extra deterioration with no chance of preservation i.e. not stored for latter use. However, during this survey local healers argue that fresh materials are effective in treatment as the contents are not lost before use compared to the dried forms. The livelihood of most traditional healers relied on fresh materials that had aggravated the decline of rare medicinal plants from the study area. Traditional practitioners were collecting medicinal plants with less attention than would be preferred from viewpoint of conservation of plant resource. Sofowora [23] has reported that the uses of fresh medicinal plants are more effective than other parts.

Of the major disease categories in the study area, infectious diseases are mainly treated traditionally using the large number of medicinal plants. This may be due to the distribution of various pathogens as a result of less sanitation and control measures in developing countries. This could also demonstrate the effort of local healers in searching out more and appropriate medicinal plant species for treatment of such diseases.

According to the informants, the majoity of medicinal plant parts of the study area are prepared either in combination with other medicinal plant parts or with other additives such as boiled coffee, honey and local bevereages (tella) for different purposes (either to increase the healing potential or to improve the flavour and taste or to avoid abdominal discomfort) [27, 28]. For instance, a traditional medicine applied to treat tape worm infection is prepared by the combination of several medicinal plant parts ( Example, Hagenia abyssinica, Glinus lotoides) with other additives such as local beverages and salt.

As indicated by preference ranking in this study, pounding and powdeing were the most frequently used methods of remedy preparation followed by presering in plastic bags as the most suitable preservation method in the study area. According to the informants’ response different methods of remedy preparation and prespervation depend upon an equipment used, prepared and preserved plant parts, temperature and preservation period. Regarding the popular medicinal plants in Ghimbi District as ranked by informants through preference ranking method Glinus lotoides was the most widely known not only by the local practioniers but also among the large local community of the study area in the treatment of tapeworm infection, followed by Echinops kebericho and Allium sativum. In contrast, [29] have recently reported that among 9 medicinal plants Croton macrostachys was the most popular in the treatment of the same (tapeworm) infection followed by Cucumis sp. Various authors have also reported the existence of popular medicinal plants in different regions of the country such as Cucumis pastulatus for Tuberculosis, Ocimum urtitolum, Rumex abyssinicus, Solanum incanum, Vernonia amygdalina to treat ‘’michi”, gonorrhea, toothache and urine retention, respectively [27‐29]. In other study reports conducted by [35] and [36] using paired comparison, preference ranking and direct matrix Allium sativum was found to be the most preferred in the treatment of malaria in the northern part of the country. Of the 9 medicinal plants ranked in the study conducted by [37] in Nigeria Azadirachta indica was reported as a prime candidate for investigation, as it recorded the highest rank by the informants. Over 1,200 plants belonging to 160 families were reported [38] to be used traditionally for the treatment of malaria. Since then the number of species has increased substantially due to the increasing worldwide interest in anti-malarial plants.

Of six medicinal plants, the highest rank was given for Carrisa spinarum followed by Curcubita pepo in the treatment of Gonorrhoea. The study conducted by [39] on antigonorrhoeal activity of some medicinal plants showed that significant antigonnorrhoeal activity was exhibited by methanol extracts of some plants, which contain bactericidal properties that stimulate the immune system to create more resistant to infection. The differences of plant species used in the treatment of the same ailment in fact depends on the availability of plant species in a particular area and cultural knowledge of particular ethnic groups.

Fidelity level (FL), as an estimation healing potential, was determined for some medicinal plants. Accordingly, Lepidium sativum and Plumbbago zeylanica were the plants having the highest level values, for their use to treat infectious and metaboilc diseases. Trotter and Logan [40], plants scoring higher informant consensus values are thought to have better potency having biologically active ingredients in treatment as compsred to plants with less informant consensus values.

The availability status of reported medicinal plant species in the study area was analyzed using an Availability Index (AI) categories developed by [20]. Accordingly, one species was reported as ‘’Rare ‘followed by ‘’Middle” 21 (45%), ‘’common” 15 (31%), and ‘’vey common” 12 (24%) species. In this study, about 47% of medicinal plant parts including root, leafy-stem and bark were reported to be used as a source of treatments. According to [22] ) medicinal plant harvests that mainly involve roots, stems and barks have serious effect on the survival of mother plants. The endangered threat status of Prunus africana throughout African counties resulted from the wide exploitation of its bark both as a source of traditional medicine and development of synthetic drug for the treatment of benign prostatic hyperplasis (BHP) and prostate gland hypertrophy (PGH). The elders of the local community of the study area expressed their great fear that the previous custom of replantation of forest species is declining by current generation. Medicinal plants are directly harvested and processed when only needs arise. Moreover, in Ethiopia the use of wild or uncultivated plants is a common custom and this has been accelerating the deterioration of useful plant population in addition to agricultural expansion accompanied by wide cutting original forest species and environmental degradation. Several studies also indicated [8, 15, 41] that a growing investment in agriculture became the major threat for the deterioration of the population of medicinal plants in general and herbs. Study by [15] also reported that the use for firewood and construction as well as agricultural expansion were the main causes for the depletion of medicinal plants in the study area.

Regarding the current transfer of indigenous knowledge in generation in the study area, this study revealed that significantly higher average number of medicinal plants (p < 0.05) were reported by informants of rural students and 25–32 age groups. This result confirmed that the traditional knowledge (TBK) is declined from elder to younger age groups. On top of this, during specimen collection, interview and field visits elders express their interest by demonstration how to collect, process, administer, and prescribe medicinal plants and with great beliefs of the traditional medicine on its effectiveness on treating the diseases while the young generation showed low participation in all aspects. Thus, decreasing positive attitude towards use of medicinal plants in traditional medicine by young generation indicate the loss of vital indigenous knowledge. Giday [40] conducted similar study using the informants of Zay Ethnic group in Ethiopia came up with 90% of the elders above 40 years possessed with enough knowledge in medicinal plants whereas 55% of the youth informants between 18 and 40 years old were without any knowledge of medicinal plants. Study conducted by [42] in Cameon reported that most young people in urban areas were not interested in the use of traditional medicine due to influence of western culture; considering that traditional medicine is superstitious, which is mainly used by poor and uneducated people. On the other hand, most of the elders kept their knowledge secrecy to generate income and to get sustainable respect from their surrounding community. More0ver, the decline of the traditional knowledge in generation is due to the due to interference of and shifts to the use of more synthetic drugs not only in the urban but also extending to the rural areas. Various reported studies indicate that the absence of formal education in traditional knowledge in developing nations is another factor for the decline of indigenous knowledge [43, 44]. Moreover, most of the African modern health professionals greatly undermine the contribution of traditional medicine in health care system while the scientists of developed nations intensively search for medicinal plants to seek a solution for the old and newly rising diseases. All these factors may result to a loss of this rich and useful knowledge which has been accumulated over many generations.

This study showed the wide use of medicinal plants in Ghimbi District in meeting the primary healthcare needs of the Oromo community of the study area. A limited access to modern healthcare facilities could be considered as the main factors for the continuation of the traditional practice. The medicinal plants in the area include all growth forms with almost equal proportion which could be attributed to their abundance in humid areas as compared to arid and semi arid regions. Newly harvested plant materials are mostly used in the preparation of remedies is an indication of the availability of copious plant materials in the vicinity. The medicinal plants in the study area such as Glinus lotoides (against tapeworm infection), Croton macrostachyus (against malaria) and Allium sativum (against malaria and other diseases) were the ones with most preferred, popular and with highest fidelity level (FL) values, an indication of their high healing potential. However, the transfer of indigenous knowledge is declining from generation to generation as a result of oral transmission. Therefore, this study recommends the argent need to incorporate this knowledge into formal education before complete lost.