Medicinal plants used to treat human ailments
A total of 213 plant species belonging to 79 families and 175 genera and a fungus species were documented and collected (Additional file 1). In terms of percentage of plant species, the family Asteraceae (25 spp., 12%) appeared to be the most dominant plant family followed by Lamiaceae (20 spp., 10%), Fabaceae (11 spp., 5%), Euphorbiaceae (9 spp., 4%) and Solanaceae (9 spp., 4%).
Ethno veterinary medicinal plants diversity
The medicinal plants used to treat livestock consisted of 95 species, in 82 genera and 48 families (Additional file 2). The most commonly mentioned plant families containing ethnoveterinary species were Asteraceae (11 spp., 12%), Lamiaceae (8 spp., 9%), Solanaceae (8 spp., 9%) and Fabaceae (6 spp., 7%).
Relative healing potential of medicinal plants: Rank order priority (ROP)
Relative healing potential of medicinal plants was computed for all reported medicinal plants. Eighty species were identified as the most preferred plants (ROP ≥ 50%). The list of most important species (ROP ≥ 50%) along with their use categories and reported study district are provided in Additional file 3. Ajuga integrifolia, Clerodendrum myricoides, Hagenia abyssinica, Ruta chalepensis, and Solanum incanum (ROP = 100%) had high fidelity level for treating infectious and intestinal parasitic diseases. Diseases of the digestive system were primarily treated by Acacia seyal, Bridelia micrantha, Ficus vasta, Maytenus heterophylla, Myrica salicifolia, and Verbena officinalis (ROP = 100%). Respiratory system diseases were mainly cured by Catha edulis, Ocimum lamiifolium, and Pittosporum viridiflorum (ROP = 100%). The genitourinary ailments were cured using Foeniculum vulgare (ROP = 95%) and Lepidium sativum (ROP = 88%); diseases of the musculoskeletal system by Ajuga integrifolia (ROP = 100%); diseases of the skin and subcutaneous tissue by Argemone mexicana, Plantago lanceolata and Salvia nilotica (ROP = 100%); rabies is mostly treated by Phytolacca dodecandra (ROP = 73%); Carica papaya (ROP = 100%) was used to cure malaria; For the category of dental and oral problems Ekebergia capensis and Datura stramonium (ROP = 100%) were found to be the most important. Liver complaints were mainly treated by Ensete ventricosum (ROP = 84%), Justicia schimperiana (ROP = 100%) and a fungus sp. Calvatia sp. (Agaricaceae) (ROP = 100%); inflammations related to anthrax were mostly treated by Brassica nigra (ROP = 100%) and Polygala sadebeckiana (ROP = 84%).
Similarity among the community based on all cited medicinal plants
Computed dissimilarity coefficient using all cited medicinal plants was above 0.5 (Table 1). In relative term, Mareqo and Muhir-Aklil showed the smallest similarity (JI = 0.26) and highest similarity (JI = 0.47) was obtained between Silti and Wulbareg districts.
High cophenetic correlation coefficient (0.92) was obtained using the UPGMA (average) clustering method, unlike the single, complete and ward methods that had cophenetic correlation coefficient of 0.90, 0.88, and 0.73, respectively. High cophenetic correlation coefficient indicates that the resulting dendrogram is a good fit of the reality. The dendrogram formed, using UPGMA (average) clustering method clustered the study sites broadly into two groups that are fairly close (Figure 3). In the first cluster A1, grouped Meskan, Sodo, Cheha, and Muhir-Aklil as deemed most similar. In Cluster A2, Qebena, Mareko, Silti and Wulbareg were grouped as similar or closely related. The first two sites in cluster A2 (Qebena and Mareqo) were outside the sub-cluster formed between Silti and Wulbareg.
Similarity among the community based on culturally most important medicinal plants (ROP ≥ 50%).
Similarity coefficient between study communities based on culturally most important medicinal plants range between 0.11-0.45 (Table 2). In relative term, the most dissimilar study sites were Muhir-Aklil and Wulbareg (JI = 0.10). Highest similarity was obtained between Cheha and Qebena districts (JI = 0.45).
Cophenetic correlation coefficient obtained using UPGMA, Complete, Ward and Single methods were 0.78, 0.77, 0.74 and 0.71, respectively. The dendrogram obtained from the UPGMA (average) clustering method grouped the study districts into two clusters but differently from the dendrogram obtained using all cited plant species (Figure 4). In cluster B1, Cheha and Qebena are grouped into the same sub-cluster while Muhir-Aklil stands alone on the same branch. On the other hand, in cluster B2 Meskan and Sodo were clustered together, also Silti and Mareqo on the same branch with Wulbareg as an out-group.
Marketability of medicinal plants
Few medicinal plants were being sold in six open markets visited. These medicinal plants are commonly used and well known by the local peoples. The medicinal plants encountered in the market places were sold or bought for medicinal and non-medicinal uses. Across the study districts, six herbs (Artemisia afra, Hagenia abyssinica, Lepidium sativum, Polygala sadebeckiana , Satureja abyssinica, and Silene macrosolen) were solely sold for their medicinal values and used as a source of income (Table 3). Thirteen plants (Allium sativum, Brassica carinata, Brassica nigra, Capsicum annuum, Carica papaya, Citrus aurantifolius, Coffea arabica, Cucurbita pepo, Lycopersicum esculantum, Ocimum basilicum, Rhamnus prinoides, Ruta chalepensis and Zingiber officinale) were sold at local markets primarily for their non-medicinal uses. All of the medicinal sellers encountered were women. The women’s pointed out that, they collect the plant/ plant parts either from their own garden, purchased from medicinal plant sellers or collected from nearby forest patches in the zones. For example, Silene macrosolen which is reported to grow mainly in the highlands of Meskan District is sold to the sellers in Agana (near to cheha), Butajira (Meskan) and Bui (Sodo) open markets. Satureja abyssinica also grows in highland areas of Cheha and Meskan districts and the people of Silti district procure the plant from Qebet open market found in the area. With regard to MPs trading, a handful or a cup of medicinal plant parts (leaves or seeds) cost a minimum price exchange of 5 birr (0.14$). An informant in Mareqo district reported that, a practice of cultivating and trading half a kilo of Jatropha curcas seeds to a neighboring healer living in Silti District worth 20 birr (0.6$).
Medicinal plants naming - Ethnotaxonomy
Nomenclature of medicinal plant sometimes involve meaning related to the plant use or other suggestive information of the plant. This was revealed in the local names of 23 medicinal plant species; 4 of the local names reflect medicinal uses and the remaining 19 species indicate morphological character (growth form, truck color and leaf shape), poisonous, test and smell of the plants (Table 4). Seventy-nine percent of the medicinal plant species have local names in one or more local languages of the studied districts that are also sometimes used similarly or with a little differed intonation among the communities. In a few cases one local name is used for many species that have similar medicinal use. For example, local name ‘Kureshe’ was used for Crinum abyssinicum, Sauromatum venosum, and Tacca leontopetaloides which are used to cure livestock ailments (anthrax and blackleg).