Background

At present, about 90 % of global food production comes from less than 30 species and more than 85–90 % of total caloric intake obtained from 12 domesticated species [1]. This situation may create an intense biotic and abiotic pressure to the modern agriculture in future. The majority of the edible plants are neglected which grow naturally in the wild and do not have to be tended before producing edible parts [2]. Such edible wild plants can significantly increase sustainability by reducing the risk of over-dependence on a limited number of crops.

The use of wild plants as food is an integral part of the culture and tradition of many indigenous communities around the world. A large section of the rural population meets their nutritional requirement through unconventional means, by consuming various wild plants and animal resources [3]. Millions of people, mostly in developing countries, derive a substantial part of their subsistence and income from wild plant products [4]. WEPs constitute an essential component in the variation of diet and bring household food security of many ethnic communities.

WEPs provide staple food for indigenous people and serve as complementary food for non-indigenous people and offer an alternative source of income [5–7]. They are an important source of nutrient, vitamin and mineral supplements for indigenous population [8, 9] and hence, reduce the vulnerability of local communities to food insecurity and thereby act as a buffer for food shortage during the emergency [10, 11]. Several researchers also demonstrated that many WEPs have nutritional or therapeutic value due to the presence of biologically active compounds, and therefore, can be considered as food-medicine and quality food [11, 12]. Many traditional leafy vegetables have higher nutritional values than several known common cultivated plants [13, 14].WEPs have substantial potential to increase the sustainability of agriculture through the reduction in multi-agricultural input. They can also be used for the development of new crops through domestication and benefit modern agriculture by providing plant breeders with a broad pool of potentially useful genetic resources for crop improvement [15, 16]. The genes for higher productivity and distinctive quality traits may be hidden in this gene pool.

Research on wild food plants is still active even in the present day. Such research is carried out in many countries and continents [17–20]. In the Indian subcontinent, 9500 wild plants are used for food, medicine, fodder, fiber, fuel, essence, cultural and other purposes by over a 53 million tribes belonging to 550 different communities [21]. Ethnobotanical studies on wild food plants associated with tribal communities of central India, Tamil Nadu, Maharashtra, Northeastern India, etc. [21–24] are reported from India. The tribal communities of the Himalayan region of India use over 195 wild edible species [25]. Wild food plants and vegetables being sold in the local markets of South Korea, Croatia, and Turkey [26–28] have also been reported. The local market provides much information on the ethnobotanical process of plant-people interaction and relationships. It represents an intensified interaction between people of different socio-economic groups and specific plants as well [29].

In spite of their immense importance as a valuable food source, WEPs remain widely unknown. Many of the wild food plants are restricted to certain areas or communities. Given the rapid decline of traditional knowledge about WEPs and increased reliance on processed food, documentation and evaluation of the traditional knowledge related to the diversity, usage, and status of WEPs are crucial. Some studies on ethnomedicinal plants have been conducted in Manipur; however, there is limited information on wild vegetables despite its diverse uses. Moreover, information on the nutritional values of most of the WEPs of Manipur is not available. Research and development activities to tap these assets for economic development and sustainability have also remained at the bottom. Many more wild species believed to be edible are yet undocumented. The rich biodiversity of wild plants will be useful in screening newer source of vegetables for present and future need. Inventory of wild food resources, ethnobotanical information on their diversity, usage, status, etc. coupled with nutritional evaluation can establish native species as an alternative to achieve food and nutritional security.

Our objective is to document and assess the diverse wild vegetable resources sold at the local markets of Manipur throughout different seasons. It also aims to provide a systematic way for prioritizing high-quality species through an integrated assessment. It will be utilized further for evaluation of nutritional components of priority species, their integration into the agricultural system and sustainable conservation and management.

Materials and methods

Study area

This study was carried out in Manipur, one of the seven states of Northeast India that forms an integral part of the Indo-Burma biodiversity hotspot. The Manipur state (23°27’ to 25°41’ N latitude and between 93°61’ and 94°48’ E longitude) comprises an area of 22, 327 km2 and administratively divided into 9 districts, of which 4 are valley (viz. Imphal East, Imphal West, Thoubal and Bishnupur) and the rest 5 are hill districts (Chandel, Churachandpur, Senapati, Ukhrul and Tamenglong (Fig. 1). The state is rich in both cultural and biological diversity, having populated by diverse ethnic, linguistic and religious groups including many indigenous tribes. Racially, Manipuri people are unique and have features similar to Southeast Asian. The state has four major ethnic communities - Meitei (Hindu), Naga and Kuki (Tribal communities) and Pangal (Muslim). The Meiteis are the dominant non-tribal community constituting 92 % of the valley area along with the Pangal (minority group), and the five hill districts are inhabited by about 34 ethnic tribes representing 30 % of the state population. They practice distinct culture and tradition and have different socio-economic features. Agriculture is the single largest occupation in Manipur and the mainstay of the state’s economy. The trade of wild vegetables provides an alternative source of income and is mainly done by women. Forests account for 67 % of the total land area of this state. The tribal communities collect a large variety of edible and other useful plants from the forest and surrounding wasteland. They also sell a large variety of such plants in the local market. The famous “Ima Keithel” (meaning “Mother’s market”) of Manipur which sells vegetables and other household items are exclusively run and controlled by women signifying their role in the society both socio-cultural and economically.

Fig. 1
figure 1

Location map of study site in Manipur, Northeast India

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A total of 20 major markets were chosen for this study as they form the primary source of supply for wild edible plants in the state –viz 1. Imphal East - Lamlong bazaar and Chingmeirong bazaar 2. Imphal West - Khwairamban keithel and Singjamei bazaar 3. Thoubal District - Thoubal bazaar and Kakching bazaar 4. Bishenpur District - Nambol bazaar, Bishenpur bazaar, Ningthoukhong bazaar and Moirang bazaar 5. Chandel District - Chandel main market and Pallel bazaar 6. Churachandpur District - New Lamka bazaar and Tuibong bazaar 7. Senapati District - Kangpokpi bazaar and Senapati bazaar 8. Ukhrul District - Yaingangpokpi bazaar and Ukhrul main market 9. Tamenglong District - Noney bazaar and Tamenglong bazaar.

Methods

Survey and data collection

The methods employed in this study were designed for collecting baseline information on the diversity and usage of wild vegetable resources locally used by people of Manipur. Before conducting the survey, prior information consent was obtained from the interviewee by explaining the aim of the study. Participants in the study were selected by purposive sampling method. The criterion was to understand and obtain maximum possible information on edibility, medicinal, dietary preference, cultural association and market of wild vegetables from various user communities to come to a generalized inference on WEPs.

Markets were surveyed to assess the presence and abundance of wild edible plants. Detailed studies were conducted at 20 major markets in all districts of Manipur from August 2012 to March 2014 in different season. Each of this market was examined twice in every season between 6.00 and 9.00 am and 2–5 pm. A total of 154 semi-structured interviews were carried out with 130 female and 24 male in the age group of 30–77 years for the collection of data. Whenever necessary, translators were used while collecting data as the participants belong to different ethnic communities. However, a majority of them know Manipuri, the state language. Detailed information was gathered using formal, informal and extensive interactions with the wild plant vendor and those involved in the collection and marketing of WEPs following the methods of Upetry et al. [18] and Jain et al. [30]. The inquiries comprise their local names, sources, life forms, growth habit, availability period, edible part, mode of consumption, availability status, distribution pattern, and mode of propagation (Table 1). The collected specimens were identified with the help of experts, relevant literature and Flora [31–34]. The plant nomenclature and author abbreviations follow The Plant List [35]. The specimens were deposited in the Herbarium of Plant Systematics and Conservation Laboratory, Institute of Bioresources and Sustainable Development, Imphal, Manipur.

Table 1 Names, Life forms, Growth habit, Edible parts, Mode of utilization, Availability period and Availability status
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Further, to perform an integrated assessment of 68 species of wild edible vegetable, the authors used Analytical hierarchy process (AHP) method [36].

Data analysis

For a systematic approach to integrated assessment, ten evaluation criteria considered important to determine the value of wild edible vegetable were selected, and a score was assigned to each of them (Table 2). These are Taste (T), Distribution (D), Community status (CS), Life form (LF), Basis of civil use (BCU), Wild or cultivated (WC), Edible time (ET), Edible part (EP), Medicinal value (MV), and Market potential (MP).

Table 2 Criteria, weight, sub-criteria and assignment score
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Weight determination

Weight determination was based on Analytical hierarchy process (AHP) method [36]. According to the relative importance of each evaluation criteria, the weight of each criterion can be determined. This paper applied the subjective weighting method. The weight of each criterion was calculated using the following steps:

  • Step1. A hierarchy was constructed based on the ten evaluation criteria viz. Taste (C1), Distribution (C2), Community status (C3), Edible time (C4), Edible part (C5), Life form (C6), Wild or cultivated (C7), Basis of civil use (C8), Medicinal value (C9), and Market potential (C10) with a total of 28 sub-criteria (Table 2).

  • Step2. This step is to define the relative importance of each criterion by making a pairwise comparison. The seven-point preference scale of Saaty [37] was used as the fundamental scale for this analysis. If two attributes were equally preferred a score of 1 was assigned, judgement moderately favoured one over other - assignment score 3, one strongly favoured over another - assignment score 5, one very strongly favoured over another - assignment score 7; intermediate values of 2,4,6 were assigned when compromisation needed in decision making. If a criterion was preferred more than the comparison criteria, the reciprocal was assigned to the comparison criteria. The use of reciprocals yields the property that (ai, j)(aj, i) = 1, where ai, j, the preference score of criterion i to criterion j; aj, i, preference score of criterion j to criterion i and ai, j = 1/aj, i [38]. Judgement matrix and consistency check of the evaluation model is constructed in Table 3.

    Table 3 Judgement of matrix and consistency check of the value criteria
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  • Step3. The weights of the decision elements were computed using the eigenvalue (λmax). The consistency index (CI) was computed from the eigenvalue as CI = (λmax- n)/ (n–1). The consistency indices of randomly generated reciprocal matrices from the scale 1to7 are called the random indices, RI. The RI for matrices of order ‘n’ is given in Table 4 [37]. The upper row is the order of the matrix (n), and the lower is the corresponding consistency index of the random judgements. The ratio of ‘CI’ to ‘RI’ for the same order matrix is called the consistency ratio (CR), which defines the accuracy of comparisons. The integrated weight of each of the index and the overall weight is then calculated.

    Table 4 RI value versus ‘n’
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  • Step4. The integrated value (IV) of each species was calculated using the following formula [39] IV = 0.19348 × T + 0.1920 × D + 0.0749 × CS + 0.0933 × ET + 0.1644 × EP + 0.0283 × LF+ 0.0358 × WC + 0.057 × BCU + 0.0324 × MV + 0.1275 × MP.

Results and discussion

Main characteristics and consumption pattern of wild edible plants

The northeast region of India, a major part of the Indo-Burma hotspot, supports considerable biodiversity. The people of the state are traditionally dependent on the wild plant resources for various cultural and religious purposes since ancient times [39]. A large variety of such edible plants are also sold in the market as a means of livelihood for the rural population. This study highlighted the rich floral diversity and the traditional knowledge of the use of wild plants as a source of vegetable by the ethnic communities of Manipur. A total of 68 wild species belonging to 42 families have been documented and collected from the market survey. The list of plants along with their local name, life form, growth habit, use category, collection period, parts consumed, mode of consumption, availability status are presented (Table 1). Of these species, 54 (79 %) are perennial while others are annual (19 %).Their growth habit includes tree, shrub, herb, climber, creeper, weed and hydrophytes. Herbaceous plants make up the highest proportion of edible plants with 31 species (46 %), followed by trees with 15 species (22 %) and shrubs with 11 species (16 %). Among the edible parts, leaves are dominant with 33 species (49 %) followed by shoot and stem with 15 species (22 %), and most of them are consumed as cooked vegetables that include boil, steam, and fry (Fig. 2). Further, 57 species (84 %) are commonly available whereas 11 (16 %) are rare. As many as 51 species (75 %) are seasonal, and 17 (25 %) are available throughout the year. Some of them are used as herbal medicine while others are used as poultry feed, fuelwood, fencing, etc. besides their use as food. The multipurpose use of these plants can be an important reason for their conservation [40].

Fig. 2
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Main characteristics showing life forms, Growth habit, edible parts and mode of consumption of WEPs

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Fig. 3
figure 3

Categories of the Integrated values of wild edible vegetables

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The communities use different modes of consumption of these species. Though the method of preparation is same, use of wild vegetables varies among communities according to their preference in taste and food habit. Singju, Eromba, Ooti, Chagempomba, Kangsoi, Champhut are the major traditional cuisines unique to the state that form an important part of daily diet. Use of one or more wild vegetables is a necessary part of a local meal. Fresh collection of vegetables before cooking is preferred.

The description of the mode of preparation of traditional dishes (Table 1) is as follows: (i) Singju, the raw dish is most common traditional food (traditional salad) made by mixing a number of wild edible species with fermented fish, chilli, and other plants (like cabbage); (ii) Eronba is prepared by boiling plant parts and smashing it with potatoes or pea, chilli, and fermented fish into a semi-liquid dish; (iii) Ootti is prepared by boiling vegetable mixture along with some rice with a pinch of sodium bicarbonate; (iv) Chagempomba is prepared by boiling soyabean, rice and different varieties of vegetables and (v) Kangsoi is a soupy dish prepared by boiling vegetable and potato with chilli, salt, fermented fish and small dried fish (see Additional file 1). Such use of WEPs in traditional delicacies was common among the tribal communities in the Himalayan Mountains [41] which explains their role in diversifying diet and fulfilling the nutritional requirement of the local system.

Analysis of evaluation criteria

Taste, market potential and medicinal value

Previous ethnobotanical surveys indicated that organoleptic traits can be used as the basis for value judgement and became criteria against which the value for a range of species could be evaluated [42]. For e.g. when the respondents are asked to choose which of the given two species is more significant or valuable to them, the response for one species being more valuable or significant than other is simply because it is tastier than the other. The survey participants indicated that the tastiest species are most commonly preferred by consumers, and have greater market potential though marketability is also influenced by other factors such as abundance, availability, distribution. Taste was the most important criterion for preference in case of leafy vegetables in southern Ethiopia [17], and also in Benin [43]. The taste criterion is based on the method of Jain et al. [30]. Some of the plants though not considered tasty are consumed by the locals for their medicinal quality or the health benefit they provided. Based on the survey data and literature review, 44 species (65 %) in the present study are with ethnomedicinal property. According to a report on wild vegetable resources in Inner Mongolia, 62 species of wild vegetable are used as medicine [38].

Distribution, community status and life form

The majority of the wild plants are distributed in most of the region whereas the rest are found in a certain area. As for the community status of the 68 species surveyed, 51 species (75 %) are common, 11 species (16 %) are rare, and 6 species (9 %) make up the dominant species. Of these species, 54 are perennial (79 %) while the rest are annual (19 %). These conditions directly influence the collection and consumption of these species.

Frequency of use and whether the plant is wild or domesticated

Based on the survey, 22 species (32 %) are widely used for frequent consumption, 42 species (61 %) are commonly used while 4 species (6 %) are rarely used. Some of the most widely used species are Euryale ferox, Chimonobambusa callosa, Ipomoea aquatica, Oenanthe javanica, Alocasia cucullata, Neptunia oleracea, Houttuynia cordata, Hedychium coronarium, Alpinia nigra, Amomum aromaticum, Eryngium foetidum, Passiflora edulis, Ficus benghalensis, Zanthoxylum budranga. It could be attributed to their taste, availability in multiple seasons or high abundance in its season and their use in various cuisines. Of the 68 species, 31 species (46 %) are semi-domesticated. They have been put into cultivation practice especially in kitchen garden while the remaining species are found in the wild. It is observed that people focus on planting those species that have good market value, taste and consumed more frequently. Usually, the tastiest species also score high concerning marketability (based on survey). Kidane et al. [17] emphasized the importance of home gardens for promotion and cultivation of prioritized leafy vegetables for ease of management, ownership, supervision and intensive cultural practices in cultivated land.

Edible parts and edible time

Sixteen species (24 %) are consumed for more than one part of the plant whereas 52 species (76 %) are collected for their single part. The edible parts include leaf, stem, fruit, root, rhizome, bud, tuber and inflorescence. Among them, leaves are dominant followed by shoot and stem and most of these are consumed as cooked vegetables. Consumption of 40 species (59 %) is single seasonal, and 28 species (41 %) are used in multiple seasons.

Integrated value

According to the integrated value (Table 5), the wild vegetables in Manipur can be classified into 4 categories (Fig. 3) – highest (integrated value > 2.5), high (integrated value 2.0 - 2.5), general (integrated value1.5 - 2.0) and low (integrated value <1.5). There are only 2 species with the highest value, 26 species with high value, 31 species with general value and 9 species with low value. Overall, 57 species (84 %) have a high or general value. Some high scoring vegetables include Centella asiatica, Euryale ferox, Chimonobambusa callosa, Ipomoea aquatica, Alocasia cucullata, Neptunia oleracea, Hedychium coronarium, Eryngium foetidum, Ficus benghalensis, Cycus pectinata, Cissus javanica, Wendlandia glabrata, and Elatostema lineolatum. It could be due to their traits of high-quality vegetables such as unique taste, appropriate edible parts, high abundance in its season, ease of processing, high market value and so on. They are also among the most preferred and frequently consumed species.

Table 5 Integrated values of evaluation criteria of the wild edible vegetables of Manipur
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An integrated assessment of wild species has not yet been done in Manipur and elsewhere except Inner Mongolia, China [38]. It provides scientific clues to select priority and high-quality species. The present study developed a new approach to the integrated assessment of wild leafy vegetables based on a set of defined criteria. The result highlighted that 57 species (84 %) have good to high value (Table 5). Among the high scoring species, Zanthoxylum budrunga, Passiflora edulis, Clerodendrum colebrookianum, Spilanthes paniculata, Cissus javanica, Elatostema lineolatum, Plantago erosa, Litsea cubeba, etc. and other species such as Zehneria scabra, Cyclanthera pedata, Piper pedicellatum, Solanum nigrum, Eurya acuminate, Solanum betaceum, Allium chinense, Heteropanax sp., Dysoxylum gobara, Diplanzium esculantum, Etlingera linguiformis, Derris wallichii, Phrynium placentarium are found to be consumed mainly by the tribal communities and rarely known to other communities. It may be due to their traditional food habit experience, preference, and local species availability. Many more such unexplored leafy vegetables are believed to exist. There is a need for exploitation of such unexplored resources given the storehouse of traditional knowledge the tribal possessed. It will provide a way for screening newer and alternative source of nutrition.

The present finding will be useful in the evaluation of nutritional components of high priority species for their integration into the agricultural system based on nutritive values. Further, assessing their cultivable potential and working towards developing agro-techniques can bring more potential species under domestication for conservation through sustainable use. Moreover, it will also help to understand their role in future food and nutritional security of the state.Therefore, documentation and prioritization would ensure that the highest priority species is preserved for use in crop improvement programs and contribute towards achieving the goal of food and nutritional security.

Traditional knowledge (TK)

WEPs constitute an integral part of the indigenous socio-ecological system associated with traditional ecological knowledge of ethnic communities. We observed that women (>40 years old) of a household possessed more traditional knowledge about leafy vegetables including the identity of the species, usage, and mode of preparation. It could be due to their association with household chores such as cooking, marketing, and their home nurturing qualities. Upetry et al. [18] have reported a similar finding. Phillips and Gentry [44] also reported that WEP knowledge is gained early in life and increases with age.

Participants in the survey have mentioned a declined in the traditional knowledge of natural resources in recent times. The cultural and traditional association of WEPs with the ethnic communities is gradually falling as they are not passed down to future generations, so present generations have little information regarding wild edibles associated with the diet of their ancestors. These generations are no longer interested in acquiring traditional knowledge of WEPs. Presumably, increasing level of modernization significantly contributes to the erosion of TK. Benz et al. [45] explained the abandoning of aboriginal ancestral practices by indigenous people in Mexico for economic and social gain. Loss of knowledge may occur if resources disappear from the landscape. Srivastava and Singh [46] have reported that frequent and overexploitation of species leads to threat in survival for some species of Northeastern States. However, the loss of indigenous knowledge worldwide has varied reasons and has been explained under local, ecological, socio-economic and cultural contexts [17]. Studying major grounds for the decline of resources and loss of associated knowledge will help decision makers in their formulations and analysis of policy [47]. Documentation and evaluation of traditional knowledge related to diversity, usage, and status of WEPs are crucial for preserving it for future generations. Support of TK systems and empowerment of its knowledge holders, promotion of the use of TK, recognition of rights of TK holders relating to their knowledge are the bottom-up approach to development [48]. It should be supported by complementary in-situ an ex-situ conservation strategies to conserve and sustainably utilize the natural resources and associated knowledge.

Conclusion

The diverse use of wild plant resources for food, medicine, income and socio-cultural purposes by the ethnic communities of Manipur revealed the high dependence on them with as many as 68 wild vegetables documented and collected. Though Manipur is bountiful in wild vegetable, a large number of them remain unexplored or known to certain sections of society. Traits that contribute to the uncommon usage of these plants include different food habits and experience of ethnic communities, the difference in taste preference, distribution, abundance and edibility time.

According to the integrated assessment, 57 out of 68 (84 %) species have good to high value. These high scoring species exhibit the traits of high-quality vegetables, such as taste, appropriate edible parts, multiple edible parts, availability, abundance, easily cultivable, simple to collect and process, and so on. To increase dietary diversity and livelihood sustenance of local people, complimentary studies and further ethnobotanical studies will be conducted. The traditional knowledge and understanding of wild food plants may serve as baseline data for future research and development activities and further biotechnological intervention. A detailed evaluation of nutritional components of the potential species should be conducted for integration into the agricultural system based on their nutritive values and for the conservation of elite germplasm. Further studies should also be done to assess their cultivable potential and work towards developing propagation and agro-techniques to bring more potential wild species under domestication for sustainable utilization of natural resources. Furthermore, proper value chain development for marketing and value-addition of selected species can facilitate enough income to native communities. Documentation and conservation of highest priority species would ensure they are available for use in genetic improvements of crop species as a contribution towards food and nutritional security. Therefore, communities should engage in sustainable management and preservation of traditional knowledge of these multi-valued resources for the well-being local communities.