Background

Afar people are pastoralists that live in the Great Rift Valley of Ethiopia. Afar Regional State is located in the eastern part of Ethiopia, bordering the State of Eritrea in the northeast, Tigray in the northwest, Amhara in the southwest, Oromia in the south, the State of Somalia in the southeast and the Republic of Djibouti in the east [1]. The Erta Ale active volcano in the Danakil depression (120 m below sea level), the lowest point below sea level in Ethiopia is found in the northern part of the region. The Afar Regional state is subdivided into five administrative zones. The population of the area based on the 2007 census is 1,390,273 consisting of 775,117 men and 615,156 women with an estimated density of 14.38 people per square kilometer [2]. The estimated area of the region is 96,707 Km2 and lies between 8° 40′13″ to 14° 27′ 29″ N latitude and 39° 51′13″ to 42° 23′03″ E longitude. The climate of the region is semi-arid to arid with erratic rainfall, and altitude ranges from 120 m below sea level up to 1500 masl. The vegetation of the area is Acacia-Commiphora (Small-Leaved Deciduous) Woodland; 31.5% shrubland, 14.8% grassland, 1.75% woodland and 0.11% forestland with a large area (49.6%) of rocky, sandy and exposed soil [3,4,5].

The people in the Afar region have the lowest health and education coverage in the country with the highest food insecurity [6]. They are a traditional society that has native and unique information exchange system by word of mouth called ‘Dagu,’ which their livelihood is very much dependent on the information transferred through Dagu system. The information ranges from weather to availability of grazing lands for their animals, and peace and security of the region [4]. Nevertheless, the cultural transformation, expansion of modern education and development in the area could detach the younger generation from such cultural values and pastoral systems that lead to loss of traditional knowledge in general, and knowledge of medicinal and edible plants in particular [7, 8].

The Afar people mostly depend on their animals and their products, and vegetation of the area as a resource for their livelihood. The animal products milk, meat, and butter are used as the primary diet, and live animals, hide, and skin generates the pastoral’s economy. The vegetation of the area is associated with significant uses such as medicine, food for human and livestock, firewood, charcoal, building materials and for making household goods [1, 9, 10]. They often move from one place to another in search of food and water for their livestock [6]. The Afar people’s livestock proportion varies accordingly with the vegetation cover of the locality. The dominant animal in the reverine forest and with better grassland are cattle and sheep, in the drier parts of the region camel and goat are dominant, and in the arid zones camels are widely dominant animal [1].

The vegetation of the area is severely affected by increased overexploitation for charcoal production and clearing forests for settlement and agriculture [3]. Some of the woody and grass species are declining such as Acacia nilotica (L.) Willd. ex Del., Acacia senegal (L.) Willd., Acacia tortilis (Forssk.) Schweinf., Balanites aegyptiaca (van Tieghem) Blatter, Cordia gharaf (Forsk.), Ziziphus spina-christi (L.) Desf. Cenchrus species and Cynodon species are the most affected and young seedlings are not usually seen growing [1, 10,11,12,13,14]. The recent incidents in the Afar region is the invasive encroaching plants; Prosopis juliflora (Sw.) DC. (Woyane), Parthenium hysterophorus L. (white top weed), and Cryptostegia grandiflora Roxb. ex R. Br. (rubber vine) are taking out multipurpose trees, grassland, and bushes and transforming the region to the mono-species thick forest. Prosopis juliflora has an effect on the total biodiversity of the area by reducing their abundance, distribution, and ecological function and replacing grassland and natural forests. It is a cause for the fast disappearing of plants used by the people as medicine and food supplements in normal time and during a food shortage. Also, P. hysterophorus and C. grandiflora are a threat to grassland and livelihood of the people in the region. The vast destruction of the natural habitats leads to a gradual disappearance of the associated traditional knowledge of medicinal and edible plants [1, 6, 14,15,16,17,18,19,20].

The Afar people, in the past, depends on milk and its’ products as main diet and edible plants of the area as a source of food in harsh times. The intensification and severity of drought caused by the climatic change, in the pastoral area, complicated and disrupted the relationship between the society and natural environment [1]. At present, because of recurrent severe drought, massive loss of livestock and dependence on relief food, the Afar People has shifted their feeding habit, and it is a cause for loss of traditional knowledge of edible plants by the younger generation [8]. According to Alemu [21], the Afar elders were aware that their traditional way of life is changing in several respects including effects of cultivation, overexploitation, and bush encroachment that would result in a declining trend in all natural resources. Moreover, Atanga et al. [6] reported, based on the interview with the older livestock herders, that 63% of grazing plant species has disappeared within 25 years from the rangelands. Hence, there is a gradual erosion of knowledge of medicinal and edible plants in the society, which requires formal ethnobotanical documentation [1, 4, 19, 20]. On the other hand, the ethnobotanical studies conducted in the Afar Region are few, and most of these studies are carried out in Awash Park where the majority of the inhabitants are Oromo People [9, 10, 14,15,16,17,18,19,20,21,22,23]. Thus, the aim of this study is to survey the traditional knowledge of medicinal and edible plants of Afar People in Yalo Woreda (District), Zone 4, Afar Regional state. The study may be used as a foundation for pharmacological and nutritional studies and identification of useful plants of the region for conservation.

Methods

Study area

A cross-sectional ethnobotanical study was conducted in eight kebeles (smallest administrative division) of Yalo Woreda from October 2015 to December 2016. Yalo Woreda is located 732 km from Addis Ababa in Zone 4, the western part of Afar Regional State; bordering Megalea Woreda in the north, Gelina Woreda in the south, Teru Woreda in the east, and Alamata Woreda in the west (Fig. 1). The landscape varies from undulating hills to flat land, and the area of the Woreda is 822.75 Km2. The climate of the Woreda is kola (Lowland) with average minimum temperature of 21 °C and maximum 38 °C and with 500 mm annual average rainfall [24]. The kebeles are Dibina (12°23′45″ N, 39°52′58″ E, 890 masl); Gidi Elea (12°16′46″ N, 39°54′31″ E, 974 masl); Kolina Gabulea (12°23′24″ N, 39°56′57″ E, 811 masl); Mesgid (12° 21′45″ N, 39°52′44″ E, 865 masl); Rekrek (12°23′9″ N, 39°52′30″ E, 893 masl); Reku Dora (12°16′46″ N, 39°54′31″ E, 974 masl); Waleae (12°17′36″ N, 39°24′11″ E, 890 masl) and Wudayili (12° 19′26″ N, 39°44′21″ E, 874 masl).

Fig. 1
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Study area. Orange tinted part shows Yalo Woreda in Afar Regional State

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The population of Yalo Woreda, based on 2006 National census, was 54,263 in which 24,418 were female, 29,845 were males, 46,511 were rural, and 7752 were urban dwellers. The majority of the population (95%) is pastoralists, and 5% are semi-pastoralists [24]. The top ten causes of morbidity in Yalo Woreda are malaria, non-bloody diarrhea, pneumonia, lung and acute upper respiratory tract infection, acute febrile illness, urinary tract infection, bloody diarrhea, infection of the skin and subcutaneous tissue, dyspepsia and severe malnutrition [25]. In Yalo Woreda, there are 2220 cattle, 20,190 sheep, 73,389 goats, 14,819 camels and 2733 equine. The top ten veterinary important diseases are PPR, pox, pasteurellosis, CCPP, external parasite, internal parasite, ORF, foot rot, salmonellosis, and brucellosis [26].

Selection of informants and collection of data

The informants were selected with the assistance of elders, and Kebele Administrative Officers. One hundred and sixty informants, 20 from each kebele, were chosen from eight kebeles using purposive sampling. Thirty-seven were females, and 123 were males. The purpose of the study was briefed to the informant, elders and Kebele Administrators to get their consent before collection of data. After receiving their informed consent, ethnobotanical data were collected using semi-structured interview, observations, field visits, and group discussion with the assistance of a native translator. The data collected were the type of diseases treated, the name of plants used for treatment, parts used, methods of preparation and dosage. The information gathered on edible plants were the name of edible plants, parts used as a food source, and seasons or availability of an edible part, and time of consumption [27].

Collections of plant specimens and identifications

The voucher plant specimens were collected from Yalo Woreda during field walks with the informants, and initial identification was conducted on the site. The specimens of plants were pressed and taken to Aklilu Lemma Institute of Pathology for identification. The specimens were further identified by an expert at National Herbarium, Addis Ababa University by using Flora of Eretria and Ethiopia and comparing with herbaria samples and deposited in National Herbarium of Addis Ababa University.

Data analysis

A descriptive statistics, percentages, and frequency were used to analyze ethnobotanical data with Microsoft Excel 2007. Statistical test; one-way analysis of variance was performed with SPSS Advanced Statistics 20.0 to compare knowledge of male and female; among age groups, and kebeles.

Informant consensus factor (ICF), fidelity level (FL) and preference ranking

The diseases and remedies reported were grouped into ten categories based on the top ten diseases in the Woreda. The categories were acute febrile illness and malaria; external injury, eye, ear nose, and mouth infections; gastrointestinal disease; impotence; internal parasites; liver infection; respiratory and lung infection; skin and subcutaneous tissue infection; swellings and cancer; and urinary tract infection. The informant consensus factor (ICF) was calculated to determine the agreements of the informants on each remedy using the formula \( ICF=\frac{n_{ur}-{n}_t}{n_{ur}-1} \). Where number of use citations in each category (nur) minus the number of species used (nt), divided by the number of use citations in each category minus one where nur is the number of use citations and nt is the number of species used [28].

Fidelity Level (FL) was calculated to determine the percentage of informants reported the uses of a medicinal plant as a remedy for the same major ailment using the formula \( \mathrm{FL}\left(\%\right)=\frac{Ip}{Iu}\times 100 \). Where Ip is the number of informants who independently indicated the use of a species for the same major ailment and Iu the total number of informants who mentioned the plant for any major ailment [29].

Preference ranking on plants that were reported by 15 and above informants that were used as a treatment for multiple diseases was conducted. Eight informants, one from each Kebele based on the number of medicinal plants reported by each informant, were selected to rank the plants according to their preference [27]. The informants were briefed on the marking of the plants that the most preferred was give the highest points (10) and least preferred was given the lowest point (1). Ten small plots labeled with one to ten was made, and each respondent was asked to put the plants in each plot. The mark given for each plant was recorded accordingly.

Ethical consideration

Institute Review Board of Aklilu Lemma Institute of Pathobiology, Addis Ababa University, reviewed and ethically approved the study. The Yalo Woreda Administrators were enlightened about the importance of the documentation of medicinal and edible plants in the Woreda before getting their permission to conduct an ethnobotanical survey in each Kebele. Likewise, Kebele Officers, elders, and informants were briefed about the primary objective of the study to enable then to decide whether to participate in the study or not before receiving their consents.

Results

Traditional knowledge

The study revealed the rich knowledge of medicinal plants in Yalo woreda that was indicated by the number and diversity of medicinal plants reported. Informants reported 106 medicinal and edible plants. The age of female informants was from 18 to 70 with a mean age of 39.38 ± 2.31 years and males from 20 to 80 with a mean age of 42.30 ± 1.10 years. The number of plants reported by females was ranging from one to six and males from one to 22. The average number of medicinal plants identified by females (2.03 ± 0.17) was less than male (3.89 ± 0.17), and the difference was significant (p < 0.05). Male parents were the primary source of traditional knowledge (TK) in the study area (Fig. 2). Male informants reported forty-two veterinary importance plants of which females reported only two, Acacia oerfota (Forssk.) Schweinf. as a treatment for goat sickness and B. aegyptiaca as a remedy for cow skin infection and itching. The average number of plants reported by young informants (18 ≤ 39) was 2.31 ± 0.20, old informants (40 ≤ 70) was 3.72 ± 0.18, and the difference was significant (p < 05). The knowledge of informants was no associated with kebeles (informant*kebeles, Eta square = 0.19). The difference among the kebeles in the number of medicinal plants reported by each informant was not significant (p > 0.05).

Fig. 2
figure 2

Traditional knowledge sources of medicinal and edible plants

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Medicinal plants of public health importance

The informants reported 102 medicinal plants with public health importance distributed into 46 family and 79 genera. Family Fabaceae had 16 Species, followed by Lamiaceae and Solanaceae with six species each, Capparidaceae with five species, Boraginaceae and Loranthaceae with four species each, Acanthaceae, Amaranthaceae, Apocynaceae, Asteraceae, Cucurbitaceae, Euphorbiaceae, Tiliaceae, and Vitaceae with three species each (Table 1; Additional file 1). All the medicinal plants were harvested from natural vegetation.

Table 1 Medicinal plants used for treatment of human and animal illness in Yalow Woreda, 2016
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Ethnoveterinary medicinal plants

Thirty-nine of the plant species were used to treat human as well as livestock diseases, but Capparis decidua (Forssk.) Edgew., Capsicum frutescens L., and Commicarpus squarrosus (Heimerl) Standl. were only used in the treatment of livestock. The plants were distributed into 21 Family and 42 genera. Fabaceae was represented by six species followed by Capparidaceae with four species, Boraginaceae, Euphorbiaceae, Solanaceae with three species each, and Aloaceae, Amaranthaceae, Apocynaceae, Balanitaceae, Cucurbitaceae, Nyctaginaceae with two species each and the rest with one species each (Table 1; Additional file 2).

Habit and parts of medicinal plants

The majority of medicinal plants were shrubs (44%), followed by herbs (28%), trees (21%), and climbers (7%). The leaf (52.94%) was used in the majority of the remedy preparations followed by root (16.99%), whole plant (6.86%), bark (5.07%), young branch (4.25%), fruit (3.27%) and stem (3.27%) (Fig. 2). The remedies were prepared from fresh (95%), dry (4%) and either fresh or dry (1%) parts. Few remedy preparation from seed (67%), whole plant (19%), fruit (15%), and bark (13%) were from dried parts whereas the majority of the remedies were prepared from fresh plant parts (Fig. 3).

Fig. 3
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Parts of plants used for the preparation of remedies

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Preparation, dosage, and mode of treatment

The majority of the treatments were prepared from a single plant (80%) and some from a mixture of multiple plants (20%). The health conditions treated with a mixture of plants were coughing blood through mouth and nostrils; knee sickness and swelling; breast swelling and infection; infant illness and fever; sleepwalking; epilepsy; devil illness; sudden illness, fever, dysentery, and vomiting; witchcraft disease; bovine brucellosis; and pasteurellosis. Forty-eight plants were used in multiple plant preparation. The most popular plants in the preparations were A. fruticosa (40%), A. tortilis (25%), B. rotundifolia (25%), Indigofera oblongifolia Forsk. (17%), C. farinosa (15%), Celosia polystachia (Forssk.) C.C. Towns. (13%), Becium filamentosum (Forssk.) Chiov. (10%) and C. rotundifolia (10%) (Table 1; Aditional Files 1 and 2).

The primary methods of preparation of remedies were crushing and pounding. The crushing and pounding were done using two stones one flat shaped and the other oval or spherical shaped to fit into the hands. The diluents were water, the blood of a black goat, and milk of goat or camel. The oral (68%) was the major route of administration of treatments followed by topical (16%), nasal (10%), eye (3%) and body wash (2%) (Fig. 4). The filtrate was applied orally, through nostril, and as an ear and eye drop. The residue was used for body washing. Camel’s milk was given as an antidote for remedies that upset or cause irritation of the stomach and honey was added to those preparations with a bitter taste. Treatments applied topically were charred, ground and the powder was mixed with butter to make a paste. The parts of medicinal plants that were inserted into a cut made in the knee, breast, or swollen body parts were mixed with salt, pepper, or butter. Fresh plants were chewed, and the juice was swallowed before a meal for a day. The remedies for some diseases were boiled in the evening, and the filtrate was taken before breakfast in the morning. Some diseases were treated with a combination of routes in both human and livestock treatments (Table 1; Additional files 1 & 2).

Fig. 4
figure 4

Routes of application of treatments

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The dosages taken orally were measured using a small coffee cup (~5 ml), glass (~20 ml), and tin can (~50 ml) for humans and large tin can (~3lt) for animals. The coffee cup was used to provide remedies to a child and tin cans for adults based on the symptoms and physical condition of the patients. The medication applied as eyedrops, eardrops and through nostrils was five to ten drops while in the treatment of animals thin bamboo stem about ten centimeters long was used. The application of remedies for flu, sleepwalking, and devil illness was inhaling the smoke, fume, and steam the patient is covered by overcoat/blanket or sniffing of crushed or powdered fresh plant parts wrapped with locally weaved close. Sniffing was not administered to children under age of five (Additional files 1 and 2). The majority of the treatments were given only once in the morning as a single dose or three times in a day or for two to seven days. However, some treatments were given only once for all animals as a vaccine to prevent and stop the transmission of the contagious disease such as CBPP, anthrax, blackleg, and bovine pasteurellosis (Additional file 2).

Fidelity value and informants consensus factor

The medicinal plants reported by few informants (one to two) or that were used only as a treatment for an ailment had FL value of 1.00. Dorstenia barnimiana Schweinf. was used as a treatment for schizophrenia, and Priva curtisiae Kobuski as a treatment for typhoid/typhus, headache, and fever and had FL value of 1.00 (Table 1). On the other hand, medicinal plants that were used to treat a variety of ailments had lower FL values. Indigofera articulata (0.25), C. farinosa (0.22), C. rotundifolia (0.19), and A. fruticosa (0.15) were used to treat diseases ranging from human to livestock and were reported by more than 20 informants.

The informant consensus factor was calculated by pulling to gather the human and animal ailments into ten categories. The values obtained were in agreement with the top ten causes of morbidity and mortality in the Yalo Woreda. Malaria and febrile diseases had the highest (ICF = 0.69) value followed by internal and liver infection (0.67), and gastrointestinal disease and internal parasite (0.62) (Table 2).

Table 2 Informant consensus value of category of diseases of public health and livestock importance in Yalow Woreda
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Preference ranking

The preference ranking of medicinal plants reported by 15 and more informants and used as a remedy for multiple diseases is shown in Table 3. The medicinal plants were ranked based on their healing potential of a disease. Balanites rotundifolia and A. fruticosa were used as remedies for diseases such as breast cancer, dyspepsia, epilepsy, ETPB, eye sickness, herpes zoster, infant disease, jaundice, lung infection, and malaria. Cadaba glandulosa Forssk. and Celosia polystachia (Forssk.) C.C. Townsend had the lowest two ranks and used as a treatment for stomach ache, bloody dysentery, fever and sudden illness. (Additional files 1 and 2).

Table 3 Preference ranking of medicinal plants predominantly cited as remedies for humans and animal in Yalo Woreda
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Edible plants and duration of gathering

Informants reported 16 edible plants and 56% of these plant species were trees and 44% were shrubs. Fourteen of the plants were nutraceutical; Rosa abyssinica R. Br. and Ximenia americana L. were used only as edible plants. All edible fruits were eaten raw (Table 4). The duration of gathering and consumption were dependent on the availability of edible parts and seasons. Boscia coriacea Pax., Carissa spinarum L., Dobera glabra (Forssk.) Poir., Mimusops kummel A. DC., R. abyssinica, Tamarindus indica L., and Z. spina-christi were gathered in Gilal as food supplements. Balanites aegyptiaca, B. rotundifolia, and Cordia sinensis Lam. were collected in Hagay as an alternative food. Grewia bicolor Juss., Grewia erythraea Schweinf., Rhus natalensis Krauss, Ruellia patula Jacq., and X. americana were gathered in Sugum-Karma and used as dietary supplements Balanites aegyptiaca, B. rotundifolia, C.sinensis, and D. glabra were sold in open markets and had economic importance.

Table 4 Edible plants consumed by Afar people in Yalow Woreda
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Discussion

Traditional knowledge and medicinal plants of human and veterinary importance

The number and diversity of medicinal plants reported by informants show the rich traditional knowledge in Yalo Woreda and the number of medicinal plants reported is more than the studies conducted in Afar and neighboring regions [10, 17, 22, 30,31,32,33,34]. The transference of traditional knowledge in the study area is from male parent to their sons since females have low status in the society and do not inherit property on the same basis to the male [4, 6]. The study conducted in Namibia indicated similar practice [35]; the females learn by routine observation whereas the boys are taught by their parents besides regular observation [22, 36,37,38,39]. The vertical transference of TK from father to son is a common phenomenon in Ethiopia, Africa, and Asia [17, 22, 35, 40,41,42,43,44,45,46,47,48]. However, studies conducted on knowledge of medicinal plants in Ankober district, Samburu district, Kenya and in South America show no difference in the average number of plants reported either by female or male respondents [47, 49, 50]. The division of labor in the society has determined the TK difference between female and male. The female informants in Yalo woreda reported only three plants with veterinary importance since the males are the sole livestock herders in the region and responsible for the animals’ wellbeing [37,38,39, 44]. The ethnoveterinary knowledge in pastoral society is acquired from their parents during grazing that indicates females’ knowledge of ethnoveterinary medicinal plants is less than men, which is similar to results reported by other studies on important ethnoveterinary plant [44, 51,52,53,54].

The number of medicinal plants reported in the study area increased with age, and the older informants reported more medicinal plants than the younger individual [36, 50, 52, 55]. Abera [56] has shown in the study conducted, in Ghimbi District, on Oromo people that the young generation is losing the interest in using medicinal plants because of changes induced by development and abandons of rural life. This phenomenon leads to the disappearance of associated traditional knowledge and interrupts transference of knowledge to next generations [16, 35, 47, 57,58,59,60,61]. Similarly, the study conducted, in the semi-arid region of Brazil, has shown that age and income difference had implications on knowledge of informants and correlated to some plants that have an effect on the traditional knowledge of younger generation [40, 50]. The transference of knowledge in the Afar family is similar to most of the pastoral areas where youngsters learn knowledge of medicinal plants from the elders during grazing. A child in Maasai pastoralists’ society in Eastern Africa has to learn and identify grasses and plants with medicinal importance in their area during grazing. The boys are taught in the field and at home, though girls are taught by their mothers and grandmothers only at home [62].

The religious establishments in Mesgid and Rekrek Kebeles and other cultural aspects had no association with traditional knowledge of medicinal plants in Yalo Wereda [63]. Though, Abu-Rabia [64] reported that knowledge of plants of nomadic pastoralists in Middle East countries originated from the sayings of Prophet Muhammad’s on health and illness: ‘The Medicine of the Prophet”. Also, the study conducted around Debre Libanos monastery has shown that the knowledge of the people varies based on the distance from the Monastery since religion is one of the aspects of variation in TK among the different societies in Ethiopia [45, 63, 65,66,67,68].

The medicinal plants reported by the people in Yalo Woreda are also reported by ethnobotanical studies conducted in semi-arid and arid regions in Ethiopia. Most of the medicinal plants are drought resistant, and many of them are a member of Acacia-Commiphora Woodland [1, 10, 17, 21, 22, 41, 46, 68]. The medicinal plants were collected from natural vegetation since the majority (95%) of the population is pastoralists, and the rest are urban dwellers without a home garden. In Ethiopia, the majority of the traditional medicines are prepared from plants collected from the wild [9, 53, 69,70,71,72,73,74]. The culture of conservation of medicinal plants in the home garden is not practiced in many regions of Ethiopia. Conservation of the medicinal plants is a requirement since the recurrent drought imposed by climatic changes has an impact on the natural vegetation. The other threat to the vegetation of the study area is the spread of invasive species such as P. juliflora that are replacing the plants with cultural values and changing vegetation to monotype bushes and forests. The people in Djibouti and Borena pastoralists areas reported a similar scenario where encroachment of invasive plants has resulted in a loss of valuable plants and degradation of the rangeland that indicates the necessity of further additional ethnobotanical studies in Afar region [1, 9, 15,16,17,18, 32, 57, 60, 75,76,77,78].

The medicinal plants reported in Yalo Woreda are also reported by other studies conducted in Afar and other areas where the Afar people are inhabitants. Bahru et al. [10] reported fourteen plant species and Beche et al. [34] reported ten plant species in the studies conducted around the Awash National Park. Meragiaw [23] reported twelve plant species in a study carried out in Aba’ala Woreda; Seifu et al. [22] reported nine plant species in a study conducted in Chifra District; and Belayneh et al. [41] reported 14 plant species in a study carried out in pastoral and agro-pastoral communities in Erer Valley of Babile Woreda. The survey conducted in the region of Randa, Djibouti reported 46 plant species [17]. The studies commonly reported Acacia mellifera (M. Vahl) Benth., .A. oerfota, .A. tortilis, B. aegyptiaca, Balanites rotundifolia (van Tiegn.) Blatter, Cadaba farinosa Forssk., Cadaba rotundifolia Forssk, Cissus quadrangularis L., Indigofera articulata Gouan, Olea europaea L. subsp. cuspidata (Wall.ex G. Don) Cif., Solanum incanum L., Withania somnifera (L.) Dunal, Ziziphus spina-christi (L.) Desf. The similarity in the naming of plants by the individuals in these study areas indicates similarity in their cultural and traditional practices. Furthermore, the use of the plants in broad geographic regions adds value to the therapeutic potential of the medicinal plants in Yalo Woreda [12, 17, 23, 34, 43, 69]. However, 29 medicinal plants are new reports by Yalo Woreda informants compared to other studies conducted in Afar region, which are used as a treatment for different health conditions in Ethiopia and elsewhere. [10, 14, 16, 32, 35, 41, 47, 48, 50, 56, 60, 62, 66, 69, 71, 76, 78,79,80,81,82,83,84,85,86,87,88,89]. Nevertheless, some of the plants are not documented in the reviewed ethnobotanical studies in Ethiopia. Citrullus lanatus (Thunb.) Matsum. & Nakai, Cyphostemma burgeri Vollesen, Dorstenia barnimiana Schweinf. that are used as a treatment for various diseases in Yalo Woreda are edible plants in other parts of Ethiopia [81, 90,92,92]. Fagonia paulayana Wagner & Vierh. used as a remedy for infant sickness in Yalo Woreda has a similar purpose to other Fagonia spp. reported in Pakistan [93, 94]. Plicosepalus robustus Wiens & Polhill is a parasitic plant that grows on Cadaba farinosa Forssk., and used as a treatment for an infection on skin and mouth, and tooth decay has a similar effect as Plicosepalus curviflorus Tiegh. and Plicosepalus acaciae Zucc. [95,96,97] with high activity against bacterial infections, and Plicosepalus nummulariifolius (Franch.)Wiens& Polhill. used as a treatment to gastritis in Djibouti [17]. Priva curtisiae Kobuski used as a treatment for typhoid, headache, and fever in Yalo Woreda has similar medicinal uses to species within the same genus; Priva cordifolia Druce, Priva flabelliformis (Mold.) R. Fernand and Priva lappulacea (L.) Pers. used as a treatment for different health conditions in Uganda and Martinique [98, 99]. Selaginella kraussiana (Kunze) A.Braun is used to treat sickness related to burning and wound; studies conducted on another species of Selaginella reported as a treatment to wound, anticancer and antimalarial in different parts of the world [100,101,102].

Fabaceae are major plant species reported as remedies to treat livestock diseases similar to other studies in the country [17,22,34.41,44,58,69,85], but in the study conducted in Ada’ar District, Afar regional state, Asclepiadaceae and Capparidaceae are dominant plant species reported as a treatment to livestock [9]. The ethnoveterinary plants reported in the current study such as A. oerfota, Acalypha fruticosa Forssk., B. aegyptiacus, Calotropis procera (Ait.) Ait.f., C. frutescens, C. quadrangularis and S. incanum. Are utilized by other societies as a treatment for varies type of animal health conditions [9, 13, 17, 20, 22, 25, 35, 41, 44, 51, 55, 71, 77, 79, 81]. Giday and Teklehaymanot [9] reported seventeen plant species in Ada’ar District, Afar Regional State; Gradé [58] reported seventeen plant species in pastoral Karamoja, Northern Uganda; Dharani [103] reported 10 plant species in East Africa and Sori [104] reported ten plant species in Borana Pastoralists, Southern Ethiopia [9, 13, 17, 20, 22, 25, 35, 41, 44, 51, 55, 69, 71, 79, 81]. The number of ethnoveterinary plants reported in Yalo woreda is more than many studies conducted in Ethiopia [30, 53, 55, 60, 70, 72,73,74, 87, 104,105,106,107,108,109] even though studies undertaken in some societies reported a higher number of ethnoveterinary plants [9, 43, 77, 104, 110, 111]. It indicates the rich knowledge of ethnoveterinary important plants in the study area since the people are highly dependent on the animals for their living [43, 58, 60, 69, 70, 104]. The Afar people seasonally migrates in search of grazing and water for their animals and utilize plants from the natural vegetation to treat animal’s illness through trial and error that profoundly contributed to the knowledge of individual herders. The plants employed for treating a disease are diverse, which is the outcome of experience gained by the various informants during grazing. The individual herder is responsible for the well-being of the livestock and uses plants found in the grazing area in addition to the knowledge passed from their parents to manage animal health conditions [9, 54, 58, 112].

Most of the medicinal plants used for the preparation of remedies were shrubs and trees that are available throughout the year. The shrubs and trees are dominantly used for the preparation of medications in most sub-arid and arid regions since the plants survive and are available in dry seasons. Trees and shrubs are used in the preparation of medications in pastoralists area such as in Borena pastoralists, 56% of remedies are prepared from trees and shrubs, and in Ada’ar District, Afar Reginal state 67.3% of ethnoveterinary plants are shrubs [9, 34, 41, 43, 48, 68, 72, 113, 120, 123]. In Yalow Woreda, the majority of remedies are prepared from fresh leaves; similar to the reports by most of the ethnobotanical studies conducted in Ethiopia and elsewhere [9,34,35 43 53,60,71,74,76] though some societies in Ethiopia prefer to use root [46, 47, 69, 72, 89, 114] and Karamoja pastoralist uses bark for the preparation of remedies [36, 57, 58, 69, 78]. The uses of the leaf would better protect the plants than roots unless the people considers in using lateral roots than the taproots, which enable the plants to draw water from depth. On the other hand, excessive defoliation could also endanger the regeneration and survival of the plants in semi-arid and arid areas [17, 60]. Fresh plant parts and leaf are predominantly used in traditional treatments in Ethiopia. The use of fresh parts lessens the depletion of ingredients that affects the healing potential of the remedies through drying and storage. The people, when using fresh plants, they assume that ingredients in the plant are not lost through drying and curing potential is more than dried once [35, 41, 46, 76, 77, 115].

The practice of single plant for remedy preparation is common than a combination treatment in many studies conducted in Ethiopia and elsewhere [9, 30, 58] Nevertheless, in some regions such as in Gindeberet district, Western Ethiopia, 94% of the preparations are made from a mixture of multiple plant species [41, 49, 54, 58, 71, 82, 113]. The number of plants in multiple plant treatment ranged from two to ten and administered to disease where single plant preparations effectiveness is low. The people in the area perceived that use of multiple plants in preparation of ethnomedicine adds up the curing potential and confer synergetic effects [58]. On the other hand, the use of multiple plants to treat a disease is an indication of the prevalence and severity of illness in the region [41, 56, 58, 113]. The most popular plants used in multiple plant preparations in Yalo Woreda and other societies are A. fruticosa [53, 104], A. tortilis [20, 54, 64, 81, 115], B. aegyptiaca [19,20,21, 53, 62, 71, 104], B. rotundifolia [104, 116], Indigofera oblongifolia Forsk. [53, 104], C. farinosa [13, 53, 116], Celosia polystachia (Forssk.) C.C. Towns.), Becium filamentosum (Forssk.) Chiov. [41, 43] and C. rotundifolia [19, 53, 116].

The primary methods of preparation of remedies, crushing and pounding and diluents such as water and milk are similarly reported by other studies in Ethiopia [58, 60, 69]. The oral is the major route of administration of treatments in Yalo Woreda and a primary route of administration reported by many studies in Ethiopia and elsewhere [51,52,53, 56, 62, 77]. The application of remedies such as eye, nasal and ear drops, body washing, and insertion into a cut made in the knee, breast, or swollen body parts are dominantly used by other studies [9, 17, 43, 44, 54, 58, 69, 78, 82, 117]. The knowledge about health conditions of both humans and animals as in many studies in Ethiopia and Africa determines the types of treatment and the dosage. The measurement of a dose is related to the effectiveness of the remedy and levels of poisoning that has been determined through long years of trial and error [48, 54, 71]. The knowledge of standard practices considered in the management of remedies in traditional human healthcare systems is important factors to determine dosage, route, and frequency of applications [69, 78]. The treatment of animals is related to the manner of feeding and physical movement and, in most case, treatment is discontinued as the animal feeding, and physical status is improved, or sign of illness disappears. The remedies are given until the animal fully recovers, or its physical conditions are improved [51, 54].

The informants in the study area had displayed high consensus values on the plants used as a remedy that indicated the popularity and therapeutic value of the plants in the society and the prevalence of the disease in the area [46, 47]. The category of diseases with high ICF values are acute febrile illness and malaria; internal, liver and gastrointestinal infection, and internal parasite. The Yalo Woreda is malarious, and the people used 37 plant species to treat the illness, and 57 plant species as a treatment for liver and gastrointestinal infections that are developed over long years of trial and error similar to other studies conducted in the country [36, 41, 72, 77, 88]. The ethnobotanical study conducted in pastoral area Samburu district, Kenya has similar result that malaria and GIT are treated with 15 to 20 medicinal plants [49]. The majority of the plants with fidelity value of 1.00 was reported by few informants (one to two) and was used only as a treatment for an ailment. Aizoon canariensis L. is used to treat devil disease and madness, On the other hand, medicinal plants that were used to treat a variety of ailments had lower FL values. The values, in such cases, may not indicate the disagreement among the informants [51, 55] rather it means that these plants are more favored by the local people in the treatment of a variety of diseases such as diphtheria, typhoid, herpes zoster, scorpion bite, devil illness, ETPB, lung infection, dysentery, breast cancer, and angina [36, 41, 51]. The medicinal plants reported by 15 and more informants and used as a remedy for multiple diseases were ranked based on their healing potential of a disease. Balanites rotundifolia and A. fruticosa are used as remedies for diseases such as breast cancer, dyspepsia, epilepsy, ETPB, eye sickness, herpes zoster, infant disease, jaundice, lung infection, and malaria [17, 40, 57, 64, 68, 69, 81]. These plants have lower FL values indicating the popularity of the plants as a treatment for a variety of diseases. Therefore, preference ranking does not necessarily indicate healing potential of plants but also their popularity and may be abundance in the study area since their fruits are edible. Other societies also report the medicinal plants as a remedy for multiple diseases such as throat infection, stomachache/diarrhea; sexual incompetence of male; body infection; skin wound, snake bite, madness, typhus, eye problem, anthrax; rabies [10, 13, 22, 37, 64, 76, 82].

Wild edible plants of Yalo Woreda

The wild edible plant parts are all eaten fresh, and duration of gathering and consumption are dependent on the availability of edible parts and seasons [34, 41, 46, 78]. The seasons are determined by the extent of rain and drought in the region. Sugum is the period of little rainfall (March to April), and Karma (June to September) is the main rain season. Gilal (October to February) and Hagay (May to June) are the dry seasons. Hagay extends to Karma and Gilal to Sugum depending on the length of rain and drought period [10,11,12, 80]. Borena, Kara, and Kwego pastoralist and people in semiarid areas in Ethiopia also consume the edible plants reported such as B. aegyptiaca, B. rotundifolia, Dobera glabra (Forssk.) Poir., Carissa spinarum L., C.sinensis, G. bicolor, G. villosa, T.amarindus indica L., X americana and Z. spina-christi [12, 13, 71, 78, 80, 118]. The people in semi-arid and arid areas rely more on edible plants compared to people that inhabit humid regions and highlands. These plants serve as food security during the dry season in semi-arid and arid areas where the recurrent drought have a dominant effect on animal’s productivity and could be developed to food crops to alleviate food shortage [78, 81, 119, 120]. Balanites aegyptiaca and B. rotundifolia and D. glabra are ‘famine food’ that are collected and stored for years in dry condition to be used in drought period to avoid starvation [12, 78, 80, 121]. These wild edible plants have been consumed by pastoralist people living in semi-arid and arid regions to alleviate food insecurity such as in the 1971 and 72 starvation in Ethiopia that severely affected Afar’s livestock. Similarly, Feyssa et al. [12] indicated that people in semi-arid and arid regions of Oromia state in Ethiopia, survived by eating fruits of D. glabra at the time of severe hunger. The wild edible fruits identified in Yalo Woreda with wider geographical distribution and altitude ranges are consumed by many societies in Ethiopia as reserve food to fill gaps between farming and harvest times where most poor farmers exhaust their crops. Unlike other parts of Ethiopia leaves, roots, and stems are not used as food in the Yalo Woreda [10,11,12,13,14, 20, 34, 46, 60, 62, 68, 78,79,80,81, 116, 119, 120, 122, 123]. Balanites aegyptiaca, B. rotundifolia, C.sinensis, and D. glabra, are sold in open markets and had economic importance [41]. Adults in eastern Sudan consume Balanites aegyptiaca, Z. spina-christi, and T. indica and have economic significance, and also have high marketability in other parts of Ethiopia [8, 34, 46, 62, 79, 123, 124].

Conclusion

The people in Yalo Woreda possess a wealth of traditional knowledge on the treatment of both human and livestock health conditions, and edible plants. Fabaceae are the dominant plant species used in Ethnomedicine preparations. The people use a variety of measurements to quantify dosage and route of application in the administration of remedies. The edible plants are used as food security and generate the pastoralist economic. All the plants with medicinal and economic importance are collected from the wide and conservation is not practiced in the area. Hence, conservation of the plants in the home garden and in the natural vegetation is a necessity against the recurrent drought and climatic changes that negatively affect the vegetation of the area, to protect the associated traditional knowledge from fast disappearing and ensure sustainable use of the plants in the traditional healthcare system. The integration of edible plants in the food sufficiency strategies in the area has to be considered since animal productivity is severely affected by encroaching invasive plants and recurrent drought. The holistic soil and water conservation policy that is being implemented in other parts of the country has to be employed in the region to save the natural vegetation that is also the repository for the medicinal and edible plants for future pharmacological and nutritional studies.