An ethnobotanical study of medicinal plants in Wonago Woreda, SNNPR, Ethiopia

Wonago Woreda (N 6° 20' and E 38° 19') is located 380 km from Addis Ababa in Gedeo Zone, Southern Nations, Nationalities and Peoples Regional State (SNNPR) and bordering with Oromia to the west and northwest, Yirgachefee to the south and southeast, Dilla to the north and Bule to the east. It is approximately 248 sq. km (24,790 ha) and comprises of 19 Kebeles (Fig. 1).

The 2005 census indicates that Wonago Woreda has a total population of 162,663 of which 78,649 (48.3%) are males and 84,014 (51.6%) are females. The population density of the Woreda is 702 persons per km² at a national growth rate of 1.07 percent. Seventy four percent of the population in the Woreda are the Gedeo people.

As the agricultural sector is the dominant means of livelihood for the majority of Wonago Woreda people, out of the total of 24,790 hectares of land in the Woreda, 22,871 hectares are known to have potential for agriculture. Annual crops cover 5.03 percent; perennial crops 84.77 percent, uncultivable land 0.65 percent and others are 3.52 percent. It has three main agro-climatic zones with the topography ranging from wide flat valley bottoms to steep mountain slopes. The rainfall distribution of the study area is bimodal. The main rainy season is from June to September ('Kiremt' or Mahar') and the short rainy season is from February to April ('Belg'). The average annual rainfall is 107.72 mm and, the mean annual average temperature of the Woreda is 20°C (Fig. 2)

The study was conducted in ten kebeles (farmers' associations) in Wonago Woreda, SNNPR from November 1, 2006 to December 3, 2006. Prior to ethnobotanical data collection, discussions were made with elders and local authorities to select the kebeles where traditional healers were found. The kebeles were selected based on availability of traditional healers, and on the recommendations of elders and local authorities in the Wonago Woreda: 'Bankookoto', 'Balebukisa', 'Deko', 'Halemo', 'Haseharo', 'Karasodity', 'Mokonisa', 'Sokicha', 'Sugale', and 'Tumata cherecha'(Fig. 1).

Thirty traditional healers (22 males and 8 females) were selected from Gedeo people in the Wonago Woreda based on the recommendation from elders and local authorities (Development Agents and Kebele administration leaders). The ages of the healers were between 35 years and 75 years. A brief group discussion was made with the informants at each kebele prior to ethnobotanical data collection to get their consent and to explain to them that their cooperation is a valuable contribution to the documentation of the traditional medicinal plants of the Wonago Woreda. Semi-structured interview, group discussion, and field observation were employed to collect data on knowledge and management of medicinal plants [7‐9]. The group discussions were conducted to elaborate the methods of preparation, administration and conservation of the medicinal plants. Interviews were conducted in "Gedeoffa" language with the help of local translator. During the study period, each informant was visited two to three times in order to confirm the reliability of the ethnobotanical information. The responses that were not in harmony with each other were rejected.

The reported medicinal plants were collected from natural vegetation and home gardens during the field walks and trees, shrubs, herbs and climbers were listed. Voucher specimens were collected, pressed and deposited in the National Herbarium of Addis Ababa University (AAU). The plants identification was performed both in the field, and at the National Herbarium of AAU [10‐16].

A descriptive statistical methods, percentage and frequency were used to analyze the ethnobotanical data on reported medicinal plants and associated indigenious knowledge.

Preference ranking was computed to assess the degree of effectiveness of certain medicinal plants against most prevalent diseases in the area. Priority ranking of factors perceived as threats to medicinal plants based on their level of destructive effects (values 1-6 were given: 1 is the least destructive threat, and 6 is the most destructive threat) and Direct matrix ranking on uses perceived as threats to medicinal plants were conducted for multipurpose medicinal plants that were commonly reported by healers [7, 9].

The Informant consensus factor (ICF) was calculated for each category to identify the agreements of the informants on the reported cures for the group of diseases. The ICF was calculated as follows: number of use citations in each category (n_ur) minus the number of species used (n_t), and divided by the numbers of use citations in each category minus one [17].

The local communities categorized the vegetation of the study area into five types based on plant density and associated landform.

II. 'Hakka Cadanaba' refers to vegetation growing in marshy or water logged areas often characterized by salty soil. Plant species such as Phoenix reclinata and Cyperus spp. were more frequent.

III. 'Mancchha' refers to a bare or with poor vegetation with some types of herbs and grasses appearing only during the rainy season.

IV. 'Bullukko' refers to the heterogeneous mixture of shrubs and grass communities not suitable for agriculture.

V. 'Wodae Gido' refers to wooded and under-growing herbaceous vegetation growing along riversides. Plant species like Spatodea nilotica, Erythrina brucei, Ficus spp. and Arundo donax were common.

155 plant species were collected from the natural vegetation, which were distributed among 63 families and 136 genera. The leading family was Asteraceae with 18 species, followed by Fabaceae with 12 species, Euphorbiaceae with 9 species, Poaceae, Solanaceae and Rosaceae each with 6 species and Myrtaceae with 5 species. Fifty-seven (37%) were herbs, 53 (34%) were shrubs, 39 (25%) were trees, 5 (3%) were climbers, and one (1%) was epiphyte [see Additional file 1].

Forty-two percent of 155 plant species were medicinal plants. They were distributed among 39 families and 63 genera. The leading family was Asteraceae with 7 species, followed by Euphorbiaceae with 6 species, Fabaceae with 5 species, Solanaceae with 4 species: 31 (49%) were shrubs, 17(27%) were herbs, and 15 (24%) were trees.

In the 'Gattae Oduma' (Home garden), the farmers grew diverse plant species with known uses. The number of plants recorded represents 65 species that belong to 33 families and 57 genera. In terms of species composition, Solanaceae had 6 species followed by Poaceae with 5 species, Asteraceae, Fabaceae, Lamiaceae and Rosaceae each with 4 species and Brassicaceae, Euphorbiaceae and Rutaceae each with 3 species (Table 1).

Out of the Sixty-five 'Gattae Oduma' plant species, 31(48%) were herbs, 23(35%) were shrubs, 7 (11%) were trees and 4 (6%) were climbers. The home gardens' flora were composed of 25 (38%) food, 10(15%) medicinal and 30(46%) other useful plant species. Majority of the plant species in the home gardens (48%) provided at least two of the uses listed in Table 2.

Most of the shrubs were collected from woodlands, rocky surfaces, secondary forests and home gardens. The herbs were mostly found in woodland, grazing land and farmlands. The tree species were found in open woodland, farm borders, roadsides, live fences and in coffee plantation areas. Medicinal plants like Allium sativum, Artemisia abyssinica, Capsicum anuum, Lepidium sativum, Ensete ventricosum, Nicotiana tabacum, Ocimum lamiifolium, Ruta chalepensis, and Zingiber officinale were restricted to farmlands, farm boarders, live fences and home gardens. Hunde [18], Mohammed [19], Tollosa [20] and Awas and Asfaw [21] used similar approaches to identify sites of collection of medicinal plants.

In this study, the number of medicinal plants collected from the natural vegetation is more than home gardens. This is also true to the studies conducted in different parts of the country. 90.43% of medicinal plants in Mana Angetu District, southeastern Ethiopia [22]; 92% of medicinal plants around 'Dheeraa' town, Arsi Zone, Ethiopia [23]; 71% of the medicinal plants of the 'Berta' people in western Ethiopia [24] and 85.71% of medicinal plants of Sekoru District, Jimma Zone, Southwestern Ethiopia [25] are obtained from the natural vegetation. Asfaw [26] reported that only 6% of the plants maintained in home gardens in Ethiopia are primarily cultivated for their medicinal value. Some of the medicinal plants cultivated provided a number of services to the local people because the primary function of these home gardens was to produce foodstuffs. This might be because of high population density and shortage of land for cultivation in the area [27].

The medicinal plant species recorded in Wonago are also used as remedies in other parts of Ethiopia and Africa. Among the total of Seventy-two medicinal plant species investigated in this study, 22 species are mentioned in Taddese [28]; 20 species in Wondimu et al. [23]; 11 species in Taddese and Demissew [29]; 23 species in Tamene [30]; 21 species in Hunde [18]; 11 species in Balemie et al. [31]; 39 species in Lulekal et al. [22]; 21 species in Teklehaymanot and Giday [32] and 17 species in Teklehaymanot et al. [33]. In Africa, 13 medicinal plant species are documented by Anokbongo [34] and 16 by Iwn [35].

Some of the medicinal plants in this study were used to treat specific diseases:Vernonia amygdalina Del., Momordica foetida Schumach, Ocimum lamiifolium Hochst. Ex Benth., and Lantana camara L. are used as treatment for malaria and associated illness in Budiope county Uganda [36]. Croton macrostachyus Del., Datura stramonium L., Eucalyptus globules Labill, Euphorbia candelabrum Kostshy, Euphorbia tirucalli L., Prunus africana (Hook.F.) Kalkam, and Ricinus communis L. in Central Kenya [37], and Calpurnia aurea (Alt.) Benth. and Phytolacca dodecandra L'Herit in Ethiopia [38] are used for treatment of skin disorders.

Allium sativum L., Lagenaria siceraria (Molina) Standl., Zingiber officinale Rosc., Capsicum annuum L, and Ricinus communis L. are used as anthelmintics in traditional veterinary practices in Sahiwal district of Punjab, Pakistan; and the anthelmintic activity of the first three medicinal plants is scientifically validated through in vitro and in vivo tests [39].

The medicinal plants that were presumed to be effective in treating a certain disease had higher ICF values, which indicated that these diseases were more common than those with low ICF: malaria and headache (82.3%), ascariasis and diarrhea (78.2%), and intestinal parasite and stomachache (77.7%).

The most widely used plant remedies by people of Wonago were obtained from shrubs (43.2%) followed by herbs (34.5%). The documented data showed that the majority of medicinal plants from natural vegetation were shrubs and herbs; they were relatively common in the study area compared to medicinal tree species. This finding agrees with the findings of Tamene [30], Hunde [18] Yineger and Yewhalaw [25], Giday and Amani [40] and Lulekal et al. [22]. However, the finding of Birhanu [41]; Mohammed [19]; Gebre [42] and Teklehaymanot and Giday [32] shows that herbs are the primary habit form.

The most widely sought plant parts in the preparation of remedies were the root [22], root bark, leaves and stems. The popularity of these parts has serious consequences from both ecological point of view and from the survival of the medicinal plant species [41]. Tesfu et al. (Tesfu CB, Mengistu B, W/Aregay G: Women lead in protecting food germplasm and herbs for health in Ethiopia, Submitted) reported that some plant species such as Dracaena steudneri, Hagenia abyssinica and Securidaca longepedunculata that are harvested for their roots, barks or whole plants in many parts of Ethiopia have become scarce and so difficult to find. On the other hand, collecting leaves alone could not pose a lasting danger to the continuity of an individual plant compared with the collection of roots, bark, stem or whole plant.

The route of application, oral (42%), is popular as in the finding of Abebe and Ayehu [43] who reported as the leading route of application used in northern Ethiopia. It is also in agreement with the result of various ethnobotanical studies conducted elsewhere in Ethiopia [18, 21, 22, 31, 40, 41, 44, 45] and indicates oral as the predominant route of application.

The informants' responses indicated that there were variations in dosages of remedies, unit of measurement of remedies, duration and time that were prescribed for the same kind of health problems. The major factors that determine the amount to be given were age, physical fitness, stage of illness, pregnancy and presence or absence of any disease other than the disease to be treated. Getahun [46], Sofowara [47] and Abebe [2] have also discussed lack of precision and standardization as a drawback of the traditional health care system.

Some traditional practitioners had started to conserve medicinal plants by growing them in home gardens. Such as Ruta chalepensis, Rhus vulgaris, Ocimum lamiifolium, Artemisia abyssinica and Artemisia afra similar to the observation made by Kansheiae [27]. In most scenarios, the home gardens are fenced and protect the medicinal plants from grazing and unwise harvesting [48].

The main threat for medicinal plants in the natural vegetation was agricultural expansion (24.4%). Most of the respondents perceived urbanization and construction as the least destructive factors contributing to 11.8% and 10.2% of the total score, respectively. The rise in Coffea arabica and Catha edulis price on the market were some of the contributing factors for the expansion of agriculture. The other factor was the number of young farmers who were anxious to have their own agricultural land; hence, clearing of natural vegetation and expanding agricultural land was almost a daily activity in the study area. Nevertheless, during the field study, it was observed that large number of big trees of Macaranga capensis, Olea europaea, Pouteria adolfi-friederici, and Syzygium guineense were removed by the local people to prepare the forestlands for agricultural purpose. These factors combined with the natural vulnerability of the area may lead to further reduction in natural habitats of the medicinal plants. Pressure from agricultural expansion, wide spread cutting for fuel wood combined with seasonal drought is also reported in Balemie et al [31], Lulekal et al. [22], Nanyingi et al., [48], Kelbessa et al. [49] and Yineger et al. [50] as main factor for environmental degradation.