Diversity of medicinal plant species and their uses
Altogether 140 medicinal plant species, including three pteridophyte species, 1 gymnosperm species and 136 angiosperms species belonging to 127 genera and 68 families were reported (Table 1). Thirty families were represented by two or more species, whereas 38 families were represented by a single species each (see details in Table 1). Asteraceae and Fabaceae were the dominant families each contributing eight species, followed by Rosaceae and Poaceae each with six species. The therapeutic dominancy of Asteraceae and Fabaceae is associated with the wide and common distribution of the family in Nepal and adjoining areas [49-58].
Fifty-five percent of the total medicinal plant species constituted herbs followed by trees (25%), shrubs (11%), and climbers (9%) (Fig. 2). Such dominance of herbs as medicinal plants is comparable with other research findings from Nepal and neighbouring countries [59-63]. Wide distribution and easy access favour the collection of herbs over other life forms such as shrubs and trees . The presence of bioactive compounds like alkaloids, phenolic glycosides and cyanogenic glycosides in herbs  makes them able to treat a majority of ailments .
A total of 83% (116 species) of medicinal plants were harvested by the local communities from the wild, while the remaining 17% (24 species) were cultivated in home gardens. Similar findings have been reported by independent studies from other parts of the world [58, 67-70]. The species harvested from the wild include 110 native species, 2 invasive alien plant species (IAPs) and four naturalized species. The species cultivated in home gardens comprise 18 introduced species and five native species. A wild buckwheat species, Eskemurkerjea megacarpum (Polygonaceae), endemic to west and central Nepal , was cultivated in the study area for its medicinal value . The majority of the IAPs and naturalized species were used for healing cuts and wounds [49, 52, 53, 62, 63, 72], while the majority of cultivated-introduced species (for example, Saccharum officinarum) were used to treat jaundice [72-75] (see Table 1 for details).
Table 1 Medicinal plant species used by the indigenous peoples’ and local communities of Chyangthapu-Phalaicha biological sub-corridor
Preparation of remedies: Bu (burnt), Co (cooked), Ch (chewing) Es. Ol (essential oil), Ex (extract), Pa (paste), Pi (pickled), Po (porridge), Pw (powder), Ra (raw), Ro (roasted), Sq (squeezed), Va (vapour), Wa (warmed)
Administrative route: O (Oral), T (Topical), I (Inhalation)
Habit: C (climber), H (Herb), S (shrub), T (Tree)
Habitat: C(e) = cultivated-endemic, C(i) = cultivated-introduced, C(n) = cultivated-native, W(ia) = wild-IAPS, W(na) = wild-native, W(nt) = wild-naturalized
The number and letter in parenthesis after the Latin names represent the voucher specimens number and the housed herbaria respectively, while ‘*’ represents the species whose samples were not collected.
Fig. 2 Life forms of medicinal plant species in the study area
Utilization of plant parts
Plant parts including the root, rhizome, tuber, stem bark, latex, leaf, aerial shoot, flower, fruit and seed and their exudates were used either singly or in combination with other parts. In some cases, multiple parts of a single species were used such that the total number of species exceed 140. The most common used plant parts were underground parts (i.e. root, rhizome, tuber-33%) followed by leaf (15%), bark (15%), fruit/seed (15%), whole plant (7%), and others (i.e. flower, latex, mature shoot, young shoot, stem, and wool for a collective total of 15%) (Fig. 3). The dominant use of underground parts may be linked to the presence of bioactive compounds in these parts [76-78]. These results agree with the previous studies [23, 49, 50, 63, 79-85]. Harvesting of the underground parts must be monitored at regular intervals for the sustainable use of the medicinal plant species [23, 86].
Fig. 3 Number of species and plant parts used
Preparation and administration of remedies
The local people in the study area use different preparation methods for administrating the remedies i.e. extract, chewing, paste, raw, powder, burnt, cooked and others. The most common method of preparing remedies was the extract i.e. decoction, juice and infusion (53%), followed by chewing (19%), paste (12%), raw (4%), powder (3%), burnt and cooked (2% each), and others (5%) (Table 2). Although there was no standardization for remedies administration [8, 76], the quantity and concentration of remedies depended on the age, illness, and diagnosis of the disease [87, 88]. Children were given lower doses, while for adults the type of diseases and their severity were the determining factors [74, 83]. Most of the remedies were given twice a day until recovery [89-91]. The measurement unit was not standardized , instead traditional techniques were used for weighing. The extract was either administered using a teaspoon (~ 5 ml) or diluted in a glass of water. Most of these remedies used water as a solvent for extraction. In some cases, honey, cow milk, egg, rock sugar, salt, and mouse droppings were used as additives. For example, a small piece (1 choito ~ 5-10 gm) of a rhizome of Nardostachys jatamansi was chewed twice a day to treat dysentery. A pinch (1 chimti ~ 5-10 gm) bark powder of Psidium guajava, dissolved in 500 ml water was consumed twice daily to treat diarrhea and vomiting. One handful (1 muthi) leaves of Taxus wallichiana was boiled in about 750 ml (1 mana) of water, and the extract was consumed twice a day to treat jaundice. A mixture of powdered Viscum album, honey (5 ml), cow milk (10 ml) and an egg was consumed to treat body pain. In case of hematuria and dysuria, a solution of Cissampelos pariera, Ocimum basilicum, Centella asiatica and rock sugar was left overnight under the open sky and consumed in the early morning. A paste of Urtica parviflora (root) and mouse droppings was effective against dog bites. Several wild plants were consumed as fresh fruits (Cassia fistula, Euodia fraxinifolia, Heracleum nepalense, Rhus javanica), while other plant parts such as tubers (Nephrolepis cordifolia), root/rhizome (Acorus calamus, Costus speciosus, Nardostachys jatamansi) and flowers (Rhododendron arboreum) were consumed raw for their nutritional and medicinal value.
The method of preparing and mode of administrating herbal remedies are related to the bioactive compounds present in the plant extract [72, 92]. Oral and topical modes of administration have been the preferred, easiest, and most effective practice in delivering bioactive compounds into the body [61, 72, 76, 81, 82, 93]. In the present study, oral administration was reported for the majority of remedies (63%), followed by topical administration (32%) and inhalation (5%) (Table 3). Nine species were inhaled either as vapour or as smoke. The hot vapour by boiling young shoots of Justicia adhatoda and the smoke from burning aerial parts of Drymaria cordata were inhaled twice a day to treat sinusitis [94-96]. The smoke of the burnt fruit of Solanaum viarum was directed towards an infected tooth to overcome the associated pain. The smoke of burnt seeds of Heracleum nepalense was inhaled to treat sneezing and the common cold , indicating that the inhalation mode was used to treat the respiratory disorders.
Altogether, 48% (68 species) of the total species cured single ailments, while 29% (40 species) cured two and 23% (32 species) cured three or more ailments (Table 1). Lobelia pyramidalis cured six ailments, while Artemisia dubia, Astilbe rivularis, Rhododendron arboreum, Urtica parviflora and Zanthoxylum armatum each cured five ailments. The plant species were used either singly or in combination to treat one or several ailments. Ficus benghalensis, Ficus religiosa, Magnolia champaca, and Rhododendron arboreum were used in combination to treat epileptic disorder. A mixture of Astilbe rivularis, Rheum australe, and Viscum album was used for body pain and ankle sprain. The paste of Clematis buchananiana, Pouzolzia zeylanica, and Ulmus laceifolia was useful for bone fracture and dislocation. The solution prepared by mixing Equisetum diffusum, Nasturtium officinale and Raphanus sativus was consumed to treat jaundice. The combined action of different species is believed to increase the catalytic activity of the medicinal constituents and accelerates its assimilation within the body . The multiple uses of these species for curing different ailments also reflect their widespread adoption of these species .
Table 2 Preparation methods for different remedies
Table 3 Administration mode for different remedies
Medicinal plant species and ailment categories
The reported medicinal plant species were used to treat 59 different health disorders in the study area. These health disorders were categorized into 12 ailment categories (Table 4). The majority of the plant species were used to treat gastrointestinal disorders (52 species), followed by general disorders (49 species) and respiratory disorders (46 species). The other categories included musculoskeletal disorders (26 species), dermatological disorders (11 species), cardiovascular disorders (7 species), genitourinary disorders (6 species), antidote, gynaecological disorders, neurological and nervous system disorders (5 species each) and socio-culture bound syndromes (2 species). The prevalence of treatments for gastrointestinal disorders was likely due to malnutrition, poor hygiene, irregular dietary routine and contaminated drinking water [64, 84, 98, 99]. Respiratory disorders can be associated with long-term exposure to indoor air pollution from traditional biomass-based fuel-wood burning and tobacco smoking [100-103]. Musculoskeletal disorders could be linked with the region’s difficult topography, labor-intensive lifestyle of the local people and the long-term conditions of other pathogenic processes [64, 104].
Quantitative analysis of ethnomedicinal use
Informant consensus factor
Informant consensus factor (ICF) tests the homogeneity of knowledge among informants in the use of plant species to treat particular ailment categories [43, 44]. In this study, the ICF was calculated for 12 ailments categories, and the range varied from 0 to 0.96 (Table 4). The highest ICF (0.96) was reported for socio-culture bound syndromes and comprised two species (Heracleum nepalense and Ligusticopsis wallichiana) with 26 use reports. This indicates that the information related to the use of these two species is well exchanged among members of the community. The ICF of musculoskeletal disorders was 0.92 with 26 species and 305 use reports followed by respiratory diseases (0.9) with 46 species and 432 use reports. The ailment category ‘sensorial disease’ has the lowest degree of consensus (0) where only two informants cited two plant species (Artemisia dubia and Iresine herbstii) suggesting no exchange of information about their uses among the informants. The socio-culture bound syndrome was preferably treated with herbal medicine  because there is no synthetic treatment available . These species should be given priority as they represent the cultural identity of the area [106, 107]. Furthermore, detailed phytochemical screening of species showing high informant consensus can aid in the transfer of local knowledge to the global level [63, 108].
Table 4 Therapeutic/Administration categories of plant species with corresponding informant consensus factor values
Relative frequency of citation
The RFC value showed a wide range varying from 2% to 86%. The most commonly mentioned MP was Swertia chirayita (43 citations, 86% RFC), which was primarily used for the treatment of fever [49, 72, 83]. This plant is commonly known as a bitter tonic in the traditional medicinal system and is used for the treatment of fever and other ailments [72, 109]. The other most cited species were Neopicrorhiza scrophulariiflora (42 citations, 84% RFC), followed by Aconitum laciniatum and Viscum album each with 41 citations (RFC 83%), used for the treatment of multiple disorders [21, 50, 59, 60, 63]. These plants have high antimicrobial, antiseptic and anti-inflammatory properties [110, 111], and were being used for similar therapeutic purposes in different localities [20, 21, 72, 83]. The high use value of these species may be attributed to easy availability, common distribution, and widespread information about their therapeutic uses within the community . The RFC of the reported medicinal plant species was 21% on average and only 16.4% species (23 species) have over 25 citations. This indicates that only few species are popular among the local communities, and immediate action is needed to preserve and document the plant species, especially those with high citations and the associated ethnomedicinal knowledge . The RFC of all the reported species is shown in Table 1.
The RI measures the usefulness of the plant species and is derived from several indicators, such as pharmacological properties of the plant species (ailments treated in our case) and the number of body systems treated . The most useful species in our study area were Artemisia dubia, Zanthoxylum armatum and Urtica parviflora (92 each) followed by Rhododendron arboreum (82), Neopicrorhiza scrophulariiflora and Astilbe rivularis (73 each) (Table 1). The high RI of these species shows their potential to cure various ailments, possesses strong pharmacological properties, and their wide use by the local communities [46, 76].
The FL index denotes the most preferred plant species used in the study area to cure a particular ailment/disease . Of the 140 medicinal plant species in total, 36 species were cited by 15 informants or more (Table 5). The major ailment was chosen based on the number of citations. The FL index ranges from 79.49% to 100%. The most preferred MP species was Swertia chirayita which was used to treat fever (100%, 43 citations), followed by Ageratina adenophora used to treat cuts and wounds (100%, 35 citations), Aconitum ferox used to treat fever (100%, 34 citations), Saussurea gossypiphora used to treat cuts and wounds (100%, 33 citations), Rheum australe used to treat body pain (100%, 31 citations), Ulmus lanceifolia used to treat bone fracture and dislocation (100%, 29 citations) and others (Table 5). The high popularity of these plant species could be attributed to their high healing potential of a particular ailment and the widespread knowledge among the informants about their uses . However, the plants with low FL or RI value should not be deemed of minor importance. The low value could mean that the traditional knowledge associated with those plant species is not being exchanged or transmitted and is on the brink of extinction . For example, the leaves of Artemisia dubia were heated over fire and applied around the eyes to reduce the pain, but only a single informant cited this therapeutic use. The single citation for this therapeutic use may be because the informants did not share the information, or synthetic drugs replaced its traditional use.
Table 5 Fidelity level of most important plant species in the study area
N = the total number of informants citing the plant species for any ailments, Np = number of respondents citing the plant species for a particular ailment.
Reliability of indigenous use reports
Indigenous knowledge on medicinal plants varies with socio-economic, demographic, historical and ecological status [114, 115]. Using a certain quantitative index, indigenous knowledge on medicinal plants in one area can be compared with others. A new ethnobiological similarity index, ‘Rahman’s similarity index (RSI)’  has recently been proposed, which compares the present study with published data from an allied, regional, national and global sources. In our study, the data was compared to 36 published literature from Nepal, the Himalayan region, the Tibetan Plateau and East Asia. The percentage of Rahman similarity varied between 0 and 12.57 among the allied area (Table 6). The highest RSI value (0.12, 12.57%) corresponds to the studies in Ilam District, East Nepal , followed by the studies in neighbouring districts of Nepal [72, 117] and adjacent areas of the Eastern Himalaya [52, 83]. The similarity index gradually decreased from East to West Nepal and reached zero with the Western Himalaya  and East Asian studies [70, 80]. The high degree of similarity with the surrounding areas can be attributed to the similar type of vegetation, geography and culture shared among each other .
Comparative analysis of this study with published literature [21, 22, 30, 49-53, 58-63, 69, 70, 72-83, 96, 112, 113, 116, 118-124] revealed some novel therapeutic uses of plant species. In total, 90 therapeutic uses were newly reported for 42 ailments representing 64 plant species (denoted as NR in Table 1). The newly documented use reports need further phytochemical research to validate the traditionally used system and to provide new insights into medical sciences.
Table 6 Rahman’s similarity index comparing the present study with previous studies
NRSAA: number of recorded plants species of aligned areas, TSCBA: Total species common in both area, SEOAA: Species enlisted only in aligned areas, SEOOA: Species enlisted only in our study area, CSSU: Common species with similar uses
Threats to ethnomedicinal plant species and conservation practices
Although over 2,000 plant species are used to treat various therapeutic ailments/diseases in Nepal , many people continue to suffer from various diseases each year. Poverty, lack of modern health care and sanitation facilities, and poor governance are among the most important reasons . The distribution of medicinal plants and associated indigenous knowledge is not uniform across the country , and a huge gap in knowledge sharing has been observed within different communities [21, 84, 125]. Traditional knowledge transmission is declining primarily due to rapid innovations in modern allopathic medicines and changes in social trends and cultural beliefs .
Medicinal plants and biodiversity are threatened by habitat fragmentation and degradation within the Chyangthapu-Phalaicha biological sub-corridor. The ongoing developmental process, such as highway construction through prime forests and red panda (Ailurus fulgens) habitat and the construction of several rural roads without proper environmental impact assessment, is a major cause of habitat fragmentation. Furthermore, the increased vehicle traffic along this highway is also likely to cause both physical and mental disturbances to the wildlife in the area. The areas adjacent to the Chyangthapu-Phalaicha biological sub-corridor, i.e. the Barsey Rhododendron Sanctuary in Sikkim and Singhalila National Park in West Bengal, are managed by the Government of India as protected areas. Unlike these areas in KL-India, the protection and monitoring of the Chyangthapu-Phalaicha biological sub-corridor is fairly low in Nepal.