Background

Home gardens are basic production units contributing to social and cultural well-being in rural areas. These units are becoming dominant and promising land-use system in many part of the tropics that maintain high levels of diversity, productivity, and sustainability endowed with important ecosystem functions [1, 2]. Home gardens have been documented as sources of a diverse and stable supply of goods and services [3,4,5]. The realization that the home gardens are also a vital reservoir of unique genetic diversity including the ethnomedicinal plants has recently led to more careful research to understand the role of home gardens as in situ genetic diversity [1, 6,7,8,9,10,11]. The opportunity of using home garden as means for conservation of crop and forest plant genetic diversity as an effective complementary measure to ex situ strategies has been reported [12]. Such traditional knowledge involved in home gardens is not only a cultural heritage but might be highly valuable for many purposes, for instance, to secure the sustainability of gardening or to conserve globally significant agro and medicinal plant diversity [3, 13,14,15]. Many traditional crop species were reported to have medicinal properties which are retained in the traditional knowledge of the local people through home gardens [16]. Medicinal plants in home gardens are either deliberately cultivated or come up spontaneously as wild and weedy species [2, 17]; they are identified as one of the key characteristics of traditional home gardens [3, 18]. They have played a major role in maintaining primary and basic healthcare of rural communities from time immemorial [19, 20].

On account of high rainfall, rich ethnic diversity, and biodiversity, Cooch Behar district, located in the foothill of North Bengal, has been witnessing a high rate of adoption of home gardens as in other humid areas [1]. Home gardens of Cooch Behar are smaller with an average size of 0.61 ha than that of other parts of India or elsewhere but are generally high in native diversity including ethnomedicinal plants [1, 7,8,9,10,11]. In India, particularly in West Bengal, people living in remote and rural areas are still dependent on traditional medicines for the treatment of various ailments due to lack of modern medical facilities and poor socioeconomic conditions [21,22,23,24,25,26,27]. Further, the elders of the region are skeptical on the retention of traditional knowledge and advocate documentation of these old age traditions and domestication of such valuable plant species for renewed interests among new generations and cultural transmissions of this valuable knowledge system [14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29]. Since traditional knowledge on ethnobotany is being eroded through modernization along with loss of plant biodiversity, documentation of this knowledge is crucial for safeguarding and preserving for future generations [28,29,30].

One of the pioneering studies on ethnobotanical study in home gardens reported only 17 species [22]. The number increased to 78 species after a decade [27, 31]. This indicates increasing use and importance given by the local community residing in the area. Both of these studies reported that the ethnobotanical plant species cultivated have actually been grown in their home garden and contributing to the conservation of the species for domestic use. Similar studies on home gardens maintaining rich biodiversity of ethnobotanical plants were also reported from Ethiopia [32,33,34,35,36]. This clearly indicates the increase in community consciousness on the conservation values of these ethnobotanical species. The practice also ensures sustainable harnessing of the valuable resource through domestication and leaving the species intact in the wild.

Raising home gardens by local people according to [37] is basically “learning to live with change and uncertainty”. The Cooch Behar district has only about 10% of its total geographical area under forest as compared to about 45% and 60% forest cover of the total geographical area in the adjacent districts of Jalpaiguri and Darjeeling, respectively [38]. We therefore expected that the garden owners of Cooch Behar district might be using and conserving the ethnomedicinal plants required for sustaining their primary nutritional care and healthcare by growing and maintaining in their own garden as there is less forest accessible to them or might be distantly located [39,40,41,42,43,44]. The national government is also now promoting and integrating the use of traditional medicines in the national healthcare through establishing a separate Ministry of Ayush. In spite of all this, the urban population accepts a new wild plant product only after a proper testimony of the specialists [27]. Though home gardens are a very common feature of this region, very limited efforts have been made for the documentation of one of its key characteristics, i.e., ethnomedicinal plants [8,9,10]. We explored and documented the diversity and population status of ethnomedicinal plants in the home gardens of Cooch Behar along with its associated traditional knowledge and use value. The information and data generated from this study can form a basis for conservation and sustainable utilization of ethnomedicinal plants and also contribute to preserve cultural and genetic diversity.

Materials and methods

Study area

The present study was carried in Cooch Behar district of West Bengal, India. The area is located in the Terai region at the northeastern part of West Bengal surrounded by the district of Jalpaiguri and Alipurduar to the north and west (Fig. 1). The area also shares state boundary with Assam to the east and international boundary with Bangladesh at south, southeast, and southwest. The district is located between 260 32′ 20″ N to 250 57′ 40″ N latitude and 89° 54′ 35″ E to 88° 47′ 40″ E longitude with an average altitude of 43 msl. Cooch Behar is characterized by humid weather and abundant rain. There is a considerable variation in the seasonal and diurnal temperature. In general, July is the hottest month while January is the coldest one. The average minimum and maximum temperature varied from 23.08 °C during winter (January) to 33.42 °C during summer (July). On an average, the annual rainfall varies from 2000 mm to 3500 mm; the bulk of which is received during premonsoon and monsoon period (May to September). The quantum of precipitation is very low during winter. The relative humidity of the area varies from 55 to 90%.

Fig. 1
figure 1

Map of the study area showing home garden locations

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The population density of the district is 832/km2 with a total population of 2,819,086 [45]. Majority of them are rural (89.70%) including indigenous people with varied socioeconomic conditions. The proportion of landless laborers is very large with 15.18% males and 4.31% females [45, 46]. The communities have their own distinct culture and belief system. The economy of the district is agriculture based, and rice is the major crop with a significant production of jute and other crops. The major occupation of the rural communities is farming. Their subsistence activity in farming includes rearing animals and growing paddy, jute, potato, other green vegetables, and maize in their marginal land holding. The rural population of the district also depends heavily on home gardens for their daily needs especially for day-to-day ailments and dietary and health supplements [10]. Therefore, every household has a home garden around their home with medicinal plants, vegetable, fruit, nuts, timber, and other plants.

Ethnobotanical data collection

A multidisciplinary approach like collection of plant specimen, interview with structured questionnaire, and focus group discussion (FGD) was conducted for data collection following [47]. The selection of the study sites in the district, i.e., Cooch Behar peri-urban locality, Pundibari, Mathabhanga, Tufanganj I, and Balarampur, was purposive while home gardens were selected randomly. Home gardens are common features of Cooch Behar district due to its humid tropical location, and every household in the district has a home garden with sociocultural and livelihood significance [1, 7,8,9, 48, 49]. Therefore, Cooch Behar district with its five main locations was selected purposefully. A representative sample of 30 home gardens each from the five villages was selected randomly with a total of 150 home gardens [50, 51].

The data were collected from May 2017 to May 2018 through personal interviews using a pretested semi-structured questionnaire containing three sections related to socioeconomic, medicinal plant diversity in home gardens and their use, and therapy [27, 50,51,52]. Prior to the interview, we tried to establish rapport with the households and pretested the questionnaire for elimination, addition, and alteration with non-sampled households. The society of the study area is patriarchal with husband/father as the head of the household. We generally interviewed the head of the household. However, sometimes the wife, the eldest son, or the daughter of the household was also interviewed when the head of the household was not available [52]. The questions were asked in local language, but the responses were recorded in English. We also conducted ten FGDs, two in each selected area with 20–25 participants which included senior citizens, home garden owners, and local medicine man. Information from these discussions was helpful to interpret our result as this supplemented our household surveys.

Sampling and data analysis

Data analysis

Considering the main objective of our study, we emphasized on documentation of the ethnomedicinal plants from the home gardens. However, floristic structure and composition of these plants were estimated considering the total species and population recorded from the home gardens. The coordinates of each home gardens were recorded by using GPS (Garmin Montana 680). The assessment of medicinal plant diversity and their composition in the home gardens was done by laying down a 10 × 10 m quadrat depending upon the area [33]. For the present study, only medicinally important species were taken into consideration based on the consumption and knowledge of the household members. Species identification was not a problem because most of the species grown were need-based and easily identified by the respondent. The plant specimens were collected, systematically tagged, pressed, dried, and mounted on herbarium sheets and were kept under presser for 2 weeks at room temperature. The specimens were poisoned in a solution of mercuric chloride and absolute alcohol (2 g mercuric chloride, dissolved in 1000 ml absolute alcohol) and mounted on the standard-sized herbarium sheets (11.5 × 17.5 in.2). The data noted in the field notebook during field survey was transferred to the label and pasted on the respective herbarium sheet on the right side at the bottom. The prepared specimens were then cross-checked and identified by a taxonomist of Angiosperms and Biosystematics Research Laboratory, Department of Botany, University of North Bengal and Department of Forestry, Uttar Banga Krishi Viswavidyalaya, West Bengal, India, with proper voucher numbers. For each home garden, the numbers of individuals for each medicinal species were recorded to determine frequency and important value index [53] to get the idea about the distribution and importance of species in these home gardens. Importance value index, a statistical quantity which gives an overall picture of a species and indicates their importance in the plant community, is the sum of relative frequency, relative density, and relative abundance. The frequency was determined by the formula:

$$ F=\frac{\mathrm{No}.\mathrm{of}\ \mathrm{home}\ \mathrm{gardens}\ \mathrm{in}\ \mathrm{which}\ \mathrm{a}\ \mathrm{species}\ \mathrm{occurs}}{\mathrm{Total}\ \mathrm{no}.\mathrm{of}\ \mathrm{home}\ \mathrm{gardens}}\times 100 $$

Use value (UVi) of the species was determined using the following formula according to [54],

$$ \mathrm{UVi}=\kern0.5em \frac{\sum Ui}{Ni} $$

where U is the number of times a species is cited and N is the number of informants. The use value of each species is therefore based objectively on the importance attributed by the informants and does not depend on the opinion of the researcher. The fidelity level (%) (FL) is measured according to [55] using the formula:

$$ \mathrm{FL}\%=\frac{I_{\mathrm{p}}}{I_u}\times 100 $$

where Ip is the number of informants who gave information of a given species as being important, while Iu is the total number of all informants mentioning important medicinal plants

To test the homogeneity of ethnomedicinal knowledge about the medicinal plants, the informant consensus factor (Fic) was used [56]. The Fic for each of the recorded plant species was calculated using the following formula:

$$ {F}_{\mathrm{ic}}=\frac{N_{\mathrm{ur}}-{N}_{\mathrm{t}}}{N_{\mathrm{ur}}-1} $$

where Nur is the number of use reports for a particular health problem and Nt is the number of species used for a particular health problem by all the informants.

To assess the importance of each species, cultural importance index (CI) was calculated by dividing the number of UR in use-category by the number of informants [57] using the following formula:

$$ {\mathrm{CI}}_{\mathrm{s}}=\sum \limits_{u={u}_1}^{u_{\mathrm{N}\mathrm{C}}}\sum \limits_{i={i}_1}^{i_{\mathrm{N}}}\frac{{\mathrm{UR}}_{\mathrm{ui}}}{N} $$

where UR is the number of use reports in various health problems (NC) and N is the total number of informants.

Result and discussion

Socioeconomic status

All of the 150 surveyed home gardens were having ethnomedicinal plant species ranging from a minimum of 1 to a maximum of 21 species. Among these gardens, 46.66% of the families were of general caste followed by schedule caste (33.33), other backward class (18%), and scheduled tribes (2%). Almost half of the respondents (47.33%) were having education of higher secondary level followed by high school (31%) and least (11%) as illiterate. Majority of the respondents (90.66%) were male, and only 9.33% were female. Most of the respondents (42.66%) were of the age group of 41–60 followed by 30.66% of above 61 and 26.66% for 20–40 year age group. Most of the home garden owners (80%) were having dependency on home gardens for their different resources like ethnomedicine, food-based items, and other ecosystem services (Fig. 2a–f)

Fig. 2
figure 2

Basic information on home gardens collated from the study area. a Range of age of the home garden (HG) in years. b Range of size of the homestead garden in hectares. c Range of number of species. d Range of number of medicinal plants. e Age of the respondents in years. f Educational status of the home garden owners

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Floristic composition

In the present study, a total of 260 plant species were recorded. Out of them, only 53 were utilized for different ethnobotanical applications (Additional file 1: Table S1). These 53 species belong to 35 families and 45 genera (Table 1). Home gardens had a specific relevance for conservation purposes due to their capacity to represent agro-biodiversity at multiple levels over small spaces and done socially [12, 58, 59]. A total of 281 plant species with 50 medicinal species from home gardens in Tehuacan Valley, Mexico, were reported [60] supporting the pattern of the present study. Documentation of 289 species of plants with 12% medicinal plants from 106 suburban home gardens in the Thimbirigaskatuwa suburban area, Western Sri Lanka, also supports the results of the present study [61]. Ethnomedicinal richness of 47 species has also been reported from home gardens of Pachmarhi Biosphere Reserve, India [62]. The reported results of [61, 62] also support to the contribution of ethnomedicinal plant species with total plant diversity from the home gardens. The earlier report of only 13 species of medicinal plants from the home gardens of North Bengal is very less as compared to the 53 species in the present study [63]. The variation may be due to the fact that the study conducted by [63] was restricted to 40 home gardens from the district of Cooch Behar. High diversity of species with an immediate use in the home is the most prominent feature of home gardens [64].

Table 1 Scientific name of documented species, families, ecological status, and other indices
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The contribution to 53 species was dominated by woody perennials (37.73%) followed by herb (28.30%), shrub 12 (22.64%), and climber 6 (11.32%), respectively (Table 2). The predominance of woody trees as a common rule in home gardens in the present study is well supported by the results of [65,66,67,68]. The contribution of fruit species is crucial for the diet of household members in terms of vitamins and fibers [69,70,71,72]. The dominance of woody trees in the present study is in contrast with the findings of [73] who found low numbers of trees in each garden, mostly because of their greater demand for space in Central Italy.

Table 2 Ethnomedicinal plant species with their uses and application procedure
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Lamiaceae was the dominant family with five genera and six species followed by Acanthaceae with three genera and four species, Euphorbiaceae with three genera and three species, and Combretaceae with one genera and three species. The highest number of individuals (160) was reported for Cocus nucifera followed by Hibiscus rosa-sinensis (143) (Table 1). Ocimum sanctum was the most frequent species followed by Cynodon dactylon (87.33%), Piper betal (85.33%), Hibiscus rosa-sinensis (80.67%), and Zingiber officinale (74.00%). The least frequent species recorded was Terminalia bellirica. The highest frequency (%) was observed in Ocimum sanctum because this species is commonly used for cold and cough and taken with hot water instead of tea everyday morning. The high individual occurrence of Cocus nucifera in these home agroforestry gardens is due to the economic viability and home consumption. The important value index (IVI) is used to determine the overall importance of each species in the community structure. The recorded average value of IVI was 5.68 with range of 2.05 to 11.06 (Table 1). The highest value of IVI (11.06) was recorded for Cocus nucifera and lowest (2.05) for Terminalia bellrica. The dominance of Cocus nucifera in home gardens of North Bengal was also reported by [1].

Parts used and ailments treated

The present study reported the leaf of 19 species as dominant plant part used as medicinal part followed by fruit (12), bark (9), root (7), and whole plant (4) (Fig. 3; Table 2). Leaves of the ethnomedicinal plants as dominant plant part to treat different diseases have also been reported by several studies [24, 25, 27, 73]. Fruit was also reported as dominant and widely used part for traditional medicines [23, 74]. These can further lead to a scientific assessment of the traditional medicines used, which may provide a lead in drug development [75, 76]. Botanically derived medicinal plants played a major role in human societies throughout history and prehistory [19, 20]. Traditional medicinal use of plants is strongly related to physiological and pharmacological activity of active plant ingredients [67]. The plant parts utilized were either taken in the form of juice, paste, decoction, powder, infusion, and chewing raw plant parts. These utilized plant parts are used to cure 20 ailments prevailing among the dependent households (Table 2). The maximum species (10) were documented for the treatment of stomach disorders followed by cough and cold (6), wounds, and jaundice of four species (Fig. 4; Table 2).

Fig. 3
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Contribution of different plant parts to ethnomedicine

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Fig. 4
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Number of species used to treat prevailing ailments in the area

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The stomach disease is prevailing in the region among all age groups due to iron rich water. The use of Aegle marmelos in stomach disorder in the present study has been supported by the findings of [77, 78] who reported it for digestive disorders. Azadirachta indica used in fever in the present study is also reported for the same by [79, 80] among different dependent communities. The use of plants as food and medicine is common among Bengali women in Sylhet, Bangladesh [81]. On the regional scale, the maximum number of medicinal plants has been reported from Uttarakhand [82] followed by Sikkim and North Bengal [83]. The hill indigenous and aborigines of West Rarrh region of West Bengal use 46 plant species ethnomedicinally in the form of infusion, decoction, oil paste, and latex either as a sole drug or in combination to treat various ailments. A study reported that 91 species of medicinal plants are used for the treatment of skin disease by the indigenous population of Darjeeling Himalayas [83]. The Rava tribe of Jalpaiguri district of West Bengal has been reported to use 41 plant species as ethnomedicine [84]. The most frequently utilized plant parts are bark, leaves, roots, branches, stem, fruits, and seeds [22, 85, 86]. Additionally, some of them have medicinal value in their flowers, rhizomes, tubers, and wood. In some cases, the whole plant including the roots was utilized [22, 30]. Most of the ethnobotanical studies confirmed that the leaves are the major portion of the plant used in the treatment of diseases [87,88,89,90,91]. We also compared these 53 medicinal plant species with the previously available literature and found 37 of them have also been reported earlier for their different uses from this region (Table 2).

Use value, fidelity, informant consensus factor, and cultural importance index

The range of use value for the documented species varied from the highest of 0.53 to the lowest of 0.006 (Table 1). The highest value of 0.53 was recorded for Ocimum sanctum followed by Centella asiatica (0.46) and Piper betle (0.28), and least value of 0.013 was observed each for Lennea coromandelica and Cinnamomum zeylanicum. The high use value (0.53) recorded for Ocimum sanctum in the study area may be due to the medico-religious significance among Hindu communities as has been described in their religious books. The highest UV was 0.48 for the species Zingiber officinale as ethnomedicinal plant has also been reported by [92] from Kurdistan, Iraq, and is in the reported range of results of the present study. Similar values of use value, for example, 0.51, 0.53, and 0.59, on ethnomedicinal species have been reported by [93,94,95], respectively, from different regions of the globe and are in well support of the present study. The fidelity value (%) of the species ranged from 2.29 to 93.75%. The highest value of fidelity (93.75%) was observed in Andrographis paniculata followed by Azadirachta indica (87.5%) and Ocimum sanctum (89.6%). The lowest value of fidelity (2.70%) was observed in Streblus asper (Table 2). The high-value species is the important medicinal plant present in the home garden, and almost every informant was aware about its values. Studies of traditional agricultural systems in tropical regions of the world provide important information for understanding ecological processes associated with sustainable management of natural resources [96].

The reported use of medicinal plants was categorized into 20 broad diseases (Fig. 4) to identify species with a particular importance in culture (Fig. 5). The highest value of Fic was reported for indigestion and stomachache (0.98) followed by cold and cough (0.96). Lowest values of Fic (0.45) were recorded for skin diseases followed by bronchitis (0.64) and fever (0.67). Also, the highest Fic value of 0.96 has been reported for gastrointestinal diseases from Pakistan. Highest Fic values of 0.80 for gastrointestinal and kidney problems followed by respiratory infections (0.72) and skin infections (0.73) have also been reported by other authors [98]. The study conducted by [24] has also reported the highest number of species for diseases like indigestion and stomachache from the forest fringe communities of North Bengal. These ethnomedicinal plants are important elements of healthcare in the region and are regarded as important cultural components. The highest value of cultural importance (CI; 0.45) was observed for Abroma augusta followed by 0.33 for Rauvolfia serpentina, Streblus asper, and Vitex negundo. The lowest value of CI (0.024) was observed for Emblica officinalis followed by 0.029 each for Euphorbia hirta and Hygrophila chulli. The cultural importance of medicinal plants has been reported by several authors throughout the globe [97,98,99] and hence can allow a resolution regarding the actual status of conservation of plants. The multiple uses of plant species for different diseases seem to be an important cause for the widespread adaptation of these medicinal plants. Ethnobotanical studies can further lead to a scientific assessment of the traditional medicines used which may provide a lead in drug development [75, 76]. A detailed knowledge of the pharmacological effect of herbal drugs is therefore necessary for effective therapy of diseases. One of the major concerns regarding the use of herbal medicines is, however, their safe usage.

Fig. 5
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Values of informants consensus factor (Fic) for different disease category

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Conclusion

The reporting of 260 species of plant diversity and 53 species as medicinal plants from a cluster of a village is an important finding of diversity maintained by the home gardens. In addition, the documentation of ecological status and ethnomedicinal practices provided important knowledge for understanding the ecological processes and their sustainable management. The study clearly indicated that a wide range of local people is dependent on home gardens, and substantial number species with medicinal values are maintained in home gardens. These gardens act as conservation centers for many of these species. The results of the study confirm that household owners have good idea about the application of these medicinal plant parts. The application of ethnomedicine from the home garden also shows their role in maintaining the family healthcare system. These findings suggest that medicinal plants and folk medicines used by the communities in Cooch Behar district of West Bengal may be an initiation for further ethnomedicine research and could lead to the conservation of the medicinal flora. The woody trees in the garden apart from providing ethnomedicine also provide good opportunities for small-scale farmers to seize the carbon market opportunities in the future.