Introduction

The global use of medicinal plants is on the rise due to the diminishing effectiveness of numerous synthetic drugs employed in the management of various chronic illnesses like coronary heart problems, hypertension, and diabetes (Ijarotimi et al. 2021). The direct or indirect use of plants has been with man since the beginning of human civilization as a result of the close connection between plants and man (Rajbhandary et al. 2020). Throughout human history, the utilization of plants, either directly or indirectly, has been a constant presence, closely intertwined with the development of human civilization (Rajbhandary et al. 2020). Among these plant resources, wild edible vegetables (WEVs) have emerged as a significant source of numerous bioactive compounds known as phytochemicals, found in substantial quantities. These phytochemicals possess antioxidant properties that can help counteract the effects of free radicals, modulate metabolic processes, detoxify carcinogens, and potentially impact pathways that influence the behaviour of tumour cells (Zhang et al. 2015). WEVs exist in many life forms, such as tuberous roots or rhizomes, leafy herbs or leaves, flowers or buds, fruits, and the seeds that are consumed as foods (Turner et al. 2011). The consumption of WEVs among rural inhabitants is connected to numerous health benefits owing to their medicinal properties and high nutritional value (Duguma 2020). Nigeria is blessed with varieties of WEVs that have gained wide acceptance as dietary constituents. They are not only known for their rich food nutrient content but also used for medicinal purposes, some of which are identified as underutilised due to civilization and inadequate information on these resources (Oseni and Babatunde 2015). In the same vein, WEVs possess some medicinal properties that are used in the treatment of some diseases. Some are used in traditional medicine for cardiovascular diseases, diabetes, weight management, and cancer as well as to improve overall body immunity (Chaturvedi et al. 2007). The consumption of vegetables in the daily diet has been strongly associated with overall good health, and reduced risk for some forms of cardiovascular diseases, diabetes, anaemia, gastric ulcer, and rheumatoid arthritis (Ayeni et al. 2020; Hyson 2002).

In developing nations such as Nigeria, where starchy foods are a predominant component of the daily diet, WEVs assume a central role in the nutrition of both rural and urban populations. This is primarily due to their affordability and accessibility, making them crucial sources of essential macronutrients and micronutrients (Adjatin et al. 2013). Various forms of WEVs, such as tuberous roots or rhizomes, leafy herbs or leaves, flowers or buds, fruits, and seeds, are consumed as foods (Turner et al. 2011). Many WEVs can be used as nutritional supplements for humans and livestock, especially vitamins and micronutrients (Duguma 2020; Mohapatra and Panda 2012). Primitive human beings traditionally chose and utilized wild edible plant species through a process of trial and error, ultimately leading to their domestication (Niveditha 2017). People have depended on wild plants for livelihood for a very long time, especially the rural dwellers who still depend on these plants to meet at least part of their daily nutritional needs or to cure different health problems (Rafiqul-Islam et al. 2019). WEVs have a significant impact on the livelihoods and food security of local rural communities, as they are traded as a source of income (Rafiqul-Islam et al. 2019).

In recent times, the increasing disappearance of WEVs from our surroundings has become more prevalent. This is primarily attributed to inadequate conservation strategies, excessive exploitation, and the absence of modern agricultural techniques that can effectively safeguard the population of these plant resources (Amujoyegbe et al. 2007).WEVs are constantly being neglected despite their richness in vital nutrients, which are crucial to humans for the maintenance of good health and the prevention of diseases. They are ignored and underutilised in favour of exotic species (Njume et al 2014). Furthermore, the potential of WEVs for income generation is still hidden due to a lack of awareness and is not available on a commercial scale because they are mostly not cultivated (Matenge et al. 2017). However, knowledge regarding the habitat, nutritional, and medicinal importance of WEVs is hardly transferred to younger generations due to a lack of keen interest expressed by the youths, hence the need for proper documentation of these important genetic resources. The primary objective of this study was to document the ethnobotanical uses of WEVs among the rural inhabitants of Ogun waterside communities.

Materials and methods

Study area

The research was conducted in the Ogun Waterside Local Government Area, situated on the South-eastern coast of Ogun State, Nigeria, along the Bight of Benin. This area covers approximately 1026 square kilometres (400 square miles) and is inhabited by a population of 103,200. Geographically, it is located at latitude 6°29′ 04′′ N and longitude 4°23′ 10′′ E (NIPOST 2020). Ogun Waterside is bordered by Ijebu-East Local Government to the Northwest, and Odigbo, Okitipupa, and Ilaje Local Government Areas of Ondo State to the Northeast, East, and Southeast, respectively. It is also adjacent to Epe Local Government and the Atlantic Ocean to the West and South respectively. The primary occupations of the residents in these sampled locations include farming, fishing, hunting, lumbering, and sand mining. This study specifically focused on eleven selected local communities within Ogun Waterside, namely: Abigi, Aiyede-ayila, Ebute-oni, Efire, Ibiade, Ilushin, Imakun-omi, Ita-otu, Itebu, Ita-ogun, and Iwopin. The choice of locations was based on the abundance and popularity of WEVs among the selected locations (Fig. 1).

Fig. 1
figure 1

Study locations selected in Ogun waterside communities in Ogun state, Nigeria

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Data collection

The collection of ethnobotanical data took place in the study area between March 2023 and July 2023. A total of eleven study locations were chosen from Ogun Waterside rural communities. These selections were made using a purposive sampling method based on the abundance and popularity of WEVs in the locations. Only one hundred and twenty respondents who volunteered to partake in the study were used. They are majorly herbalists, herb sellers, and farmers, comprising 83 males and 37 females who have prior knowledge and utilise the WEVs. At least 10 respondents were selected from the eleven local communities within the entire study area. Data were gathered through the use of semi-structured questionnaires, which encompassed inquiries about various aspects of WEVs. This method for the selection of participants in the study was a focus group that used and was acquainted with the WEVs. These questionnaires sought information regarding the local names of the plants, their availability, parts of the plants used, their natural habitats, methods of preparation, as well as their culinary and medicinal applications. It’s worth noting that some of these vegetables are considered naturalized in the study area. Before conducting the ethnobotanical survey, explicit consent was obtained from the head of each village and individual informants. This was done in strict adherence to the ethical guidelines outlined by the International Society of Ethnobiology (ISE Code of Ethics, 2008). Subsequently, field studies and interviews were conducted following these ethical principles and guidelines. Plant specimens, which included information such as the local name, date of collection, collection number, collector’s name, plant description, and location of the plant, were carefully pressed and labelled. These labelled specimens were then transported to the Forest Herbarium Ibadan.

Data analysis

In this study, the demographic characteristics of the respondents, number of WEVs collected, families, local names, habitat, life forms, parts used, and preparation methods were analysed by descriptive statistics such as tables, graphs, percentages, and pie charts. The ethnobotanical indices, relative frequency of citations and fidelity level for each plant use were analysed using the methods described by Tardío and Pardo-de-Santayana (2008) and Chaachouay et al. (2019), respectively.

$$Relative Frequency of Citation=\frac{FC}{N}$$
(1)

where

FC – Number of mentions for a particular wild edible plant species.

N – Overall count of participants providing information in the study.

Fidelity Level (FL): It is calculated by taking the ratio of the number of interview participants (Ns) who independently recommended a specific plant species for the treatment of a particular illness to the total number of interview participants who reported using plants for any purpose.

$$Fidelity level \left(FL\right)= \frac{Ns}{N} x 100$$
(2)

Ns – Number of participants providing the use for a particular plant species to treat a specific disease.

N – Number of participants in the study.

Results and discussion

Demographic overview of the informants

This demonstrates that there are notable disparities in the understanding of WEVs among various social groups. The findings indicate that men (62.5%) possess a more substantial level of knowledge compared to women (37.5%). When comparing the knowledge of WEVs between male and female informants, it becomes evident that a distinct knowledge gap exists between the two groups. This shows that free knowledge is shared among male family members rather than female family members. This may be a result of the fact that most of the respondents engaged in major occupations (farming, herb selling, and herbal medicine practices), which are dominated by males in the study area. This may have led to more free interaction among the male folds than the female counterparts (Table 1).

Table 1 Demographic attributes of respondents in the selected Ogun waterside communities in Nigeria (n = 120)
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This finding negates previous ethnobotanical studies (Cruz et al. 2013; Joshi et al. 2018; Tahir et al. 2023). However, some studies have shown that females often tend to have better traditional knowledge, because they mostly participate in activities that support their households and provide sustenance to their families (De-Costa et al. 2021). This culturally acquired knowledge is integrated with everyday information to enhance the livelihoods of their families (Singh et al. 2016). There was also a disparity in WEV knowledge between informants’ age groups; older people knew more WEVs than adults and young people (Table 1), as was also indicated in other similar ethnobotanical studies (Bortolotto et al. 2015; Cheng et al. 2022). This phenomenon may be linked to the hesitance or unwillingness of young individuals to acquire and pass on knowledge of wild edible plants, as observed similarly in an ethnobotanical study reported by Ghanimi et al. (2022). From the perspective of educational attainment, there was a notable disparity in wild edible plant knowledge among individuals with varying levels of education. This indicates that individuals with lower formal education or those who are illiterate tended to possess more extensive knowledge in this field compared to their more highly educated counterparts (Table 1). This might be a result of illiterate and semi-illiterate respondents’ livelihoods depending on agricultural activity, whereas non-agricultural jobs are preferred by most educated people (Cheng et al. 2022). From the perspective of informants’ occupations, the knowledge difference in the number of WEVs reported between different occupations was evident in the result. Herbalists (40.8%), farmers (24.2%), and herb sellers (20.8%) hold more knowledge than informants with other occupations (14.2%) respectively (Table 1). The result is similar to the earlier report by Cheng et al. (2022), who also affirm that traditional knowledge of plants is commonly found among people who are herbalists, herb sellers, and farmers.

Culinary uses of wild edible vegetables

Regarding the culinary applications of WEVs reported by the respondents in the chosen locations within the Ogun Waterside rural communities, most of these WEVs are either consumed in their raw form as ingredients in salads or as garnishes for various dishes. Alternatively, they are cooked and used in vegetable soups or as seasonings and condiments to enhance the flavour of food (Table 2). In the present study, the most significant edible species are typically utilized as key ingredients in soup preparations, adding to the delicacies of the dishes are Corchorus olitorius L., Vernonia amygdalina Delile, Telfairia occidentalis Hook. f., Talinum triangulare (Jacq.) Willd, Solanum macrocarpon L., Solanum americanum Mill, Celosia leptostachya Benth, Launaea taraxacifolia (Willd.), Amin ex C. Jeffrey, and Solanecio biafrae (Oliv. & Hiern) C. Jeffrey. Fruits of Abelmuscus esculentus (L.) Moench are cooked as soup, while the seeds of Parkia biglobosa (Jacq.) R. Br. Ex G. Don, Prosopis africana (Guill. & Perr.) Taub, Cucurbita pepo L. and Beilschmiedia mannii (Meisn.) Benth & Hook. f. are subjected to a series of processing under specific procedures into more nutritious foods that are consumed as condiments. A similar outcome was documented in an ethnobotanical study involving P. africana, Irvingia wombolu Vermoesen, Celosia argentea L., P. biglobosa, and C. olitorius (Shomkegh et al. 2013). Consistent with previous reports, their extensive knowledge of these wild resources underscores their significant role as dietary components, forming an integral part of their diets (El-Finou et al. 2023). This knowledge is of utmost importance in shaping the food culture of both the Nigerian population and Africa as a whole, as supported by previous studies (Hart et al. 2005; Sunday et al. 2021). In the study area, the identified common categories of WEVs include leafy vegetables (46.9%), culinary herbs and spices (21.9%), edible seeds (15.6%), edible stems (6.3%), and edible fruits and tubers (9.4%).

Table 2 Wild edible vegetables consumed as foods and used as traditional medicine by rural dwellers in selected Ogun waterside communities, Nigeria
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Medicinal uses of wild edible vegetable species

Among the forty-one ailments and illnesses reported by the respondents, the most commonly treated disease categories with WEVs in the study area are inflammatory conditions (such as rheumatism, arthritis, wounds, ulcers, blood impurities, and anaemia), gastrointestinal issues (dysentery, diarrhoea, constipation, and stomach aches), chronic diseases (kidney failure, diabetes, obesity, and hypertension), and respiratory ailments (asthma, cough, and cold) as presented (Table 2). It is important to note that the use of WEVs extends beyond nutritional purposes and encompasses traditional medicine. This suggests that WEVs play a crucial dual role in both ensuring food security and contributing to healthcare within the communities in this region. In this study, a decoction of mature seeds of B. mannii is consumed orally once daily as a potent remedy for rheumatism. Meanwhile, crushed or cooked leaves of Clerodendrum volubile P. Beauv and Ipomoea batatas (L.) Lam are taken orally as remedies for arthritis, pain and fatigue. For ulcer treatment, juice extracted by squishing the leaves of C. olitorius is taken twice daily. Also, the mature leaves of T. triangulare, C. olitorius, J. tanjorensis, C. argentea, and T. occidentalis are cooked, consumed as vegetables, or squished to obtain the juice, which is taken orally twice daily for treating anaemia. However, diarrhoea is treated by eating the leaves or the juice squished from the leaves of O. gratissimum, C. olitorius, and C. argentea. While dysentery is treated orally by taking an infusion made from A. esculentus fruits or I. batatas leaves soaked in water overnight. An infusion of Amaranthus spinosus L. leaves soaked in water or alcohol for 2 days is used as a potent remedy for kidney-related illnesses. Additionally, an infusion made from S. biafrae, A. spinosus Linn O. gratissimum leaves, and A. esculentus fruits soaked for 72 h is used orally as an anti-diabetic. Also, the juice obtained by squishing the leaves of V. amygdalina, L. taraxacifolia, and I. batatas is used as a treatment for diabetes. For obesity, the leaves and stems of Crassocephalum ruibens (Juss. Ex Jacq.) S. Moore is cooked and eaten regularly as a vegetable for weight control. The leaves of S. biafrae, Manihot esculenta Crantz, J. tanjorensis, or T. triangulare, made into an infusion or decoction, or cooked as a vegetable are  used orally as an anti-hypertensive remedy. Again, the juice of V. amygdalina and C. olitorius leaves obtained by squishing is taken orally against measles. An aqueous infusion from S. americanum, C. pepo leaves, and A. esculentus fruits is used as a treatment for microbial infections, including gonorrhoea. Whereas, an infusion made from the leaves of Allium fistulosum L is used orally once daily as a remedy for cancer. Equally, an infusion made from Allium cepa L. and Allium sativum L. bulbs is used orally as an active remedy for tuberculosis. In the same vein, an infusion combo of A. cepa, A. fistulosum, and A. sativum bulbs is used orally daily for treating asthma and coughs. Rhizomes of Zingiber officinale Roscoe are crushed into a paste and mixed with hot water and the resultant mixture is taken orally twice daily as a remedy for asthma and colds. The mature seeds of P. biglobosa and P. africana are fermented in water for 4 days and then crushed, the resultant products are consumed as remedies for eye problems and headaches, respectively. The WEVs considered are highly valuable due to their numerous medicinal properties, widespread availability, and potency, as evidenced by their relative frequency of citation (RFC) greater than 0.30. These species include V. amygdalina (0.77), C. argentea (0.73), T. triangulare (0.72), T. occidentalis (0.67), C. olitorius (0.61), J. tanjorensis (0.40), O. gratissimum (0.35), A. hybridus (0.32) and P. biglobosa (0.30). The medicinal uses reported in these study locations are similar to the medicinal uses of WEVs that were reported in the previous study (Alfred 2020) and also align with the results of a previous ethnobotanical study conducted in Ekiti State, Nigeria, where similar species were also documented (Arowosegbe et al. 2018).

Inventory of wild edible vegetable species

The study of WEVs has resulted in the identification of an inventory comprising 32 species, distributed into 26 genera and 15 families (Table 2). Notably, all 32 species mentioned by the informants are recognized for both their nutritional and medicinal properties. The Amaranthaceae, Asteraceae, and Lamiaceae were found to be the most prominent WEV families, having four species each. Amaryllidaceae was the second most popular WEV family with three species, followed by Cucurbitaceae, Euphorbiaceae, Fabaceae, Malvaceae, Solanaceae, and Zingiberaceae each with two species, while Basellaceae, Convolvulaceae, Irvingiaceae, Moringaceae, and Talinaceae had one species (Fig. 2). In the current study area, Amaranthaceae, Asteraceae, and Lamiaceae are the dominant WEV families. This may be ascribed to the fact that the majority of WEVs consumed by the inhabitants of the 11 rural communities sampled belong to three prominent families reported in this study locations. This finding is in line with the submission of Alfred (2020) who had earlier reported the same number of WEVs in the ethnobotanical study conducted in the Eastern Cape Province, South Africa where Amaranthaceae and Asteraceae were among the most popular plant families with at least 4 species. This similarity may be related to the abundance of WEVs in the Amaranthaceae, Asteraceae, and Lamiaceae family. In addition, the result in this study also supports the report of Achigan-Dako et al. (2011) in a related study focusing on vegetable diversity across 49 villages in Benin, which affirmed that Amaranthaceae and Asteraceae, were among the 5 most frequently used families (Amaranthaceae, Asteraceae, Cucurbitaceae, Fabaceae and Solanaceae) utilised as vegetable resources all over the country. This may be linked to the fact that a large number of commonly used WEVs by the locals in the study areas belong to these families (Achigan-Dako et al. 2011).

Fig. 2
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Family of selected wild edible vegetable species used in Ogun waterside rural communities

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Edible parts of WEVs used

The utilization of different parts of WEVs within the study locations, both for their nutritional and medicinal values, is ranked in decreasing order of significance as follows: leaves (57%), stem-bark (16%), seeds (11%), bulbs (9%), rhizomes (5%), and fruits (2%). Aerial parts of the plants constitute the majority of use (86%), while underground parts, including bulbs and rhizomes, make up the smaller proportion (14%), as illustrated (Fig. 3). This discovery aligns with previous studies that have also highlighted leaves as the dominant plant part used for both food and medicinal purposes (Bammou et al. 2015; Manlosa et al. 2019; Olowo et al. 2022; Umartani and Nahdi 2021; Welcome and Wyk 2019). The extensive use of leaves may be attributed to the fact that leaves often serve as a storage site for essential micronutrients and secondary metabolites responsible for the plant’s biological properties (El-Finou et al. 2023).

Fig. 3
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Plant parts of selected wild edible vegetables used in Ogun waterside rural communities

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Life-forms of WEVs used

In this study, it was observed that more than half of the reported plant species were categorized as herbs (56.3%), followed by shrubs (12.5%) and climbers (12.5%), as illustrated (Fig. 4). This finding aligns with research conducted by Nutuli et al. (2012) on edible vegetables in Kwazulu-Natal province, South Africa, where herbs were also the dominant category (65%), followed by climbers (24%). Furthermore, ethnobotanical studies on edible vegetables in various African countries, including Morocco, Benin, Ethiopia, Cameroon, Kenya, and Guinea-Bissau, have consistently highlighted the prevalence of herbaceous plants, with overall percentages ranging from 61.5% to 64.5% (Catarino et al. 2019; Ngone et al. 2016).

Fig. 4
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Life-form of selected wild edible vegetables used in Ogun waterside rural communities

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Mode of preparation of WEVs used

The utilization of WEVs for medicinal purposes involves various modes of preparation, depending on the part of the plant being used. In this study, it was found that the majority of herbal remedies are prepared through cooking (9), infusion (8), and squishing (8), as depicted in Fig. 5. This aligns with the findings of a study conducted by El-Finou et al. (2023) where the majority of remedies were also prepared by infusion. According to the beliefs of the majority of respondents, these modes of preparation, namely cooking, infusion, and squishing, are considered the most effective methods for extracting the most active principles from certain recipes.

Fig. 5
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Mode of preparation of selected WEVs used in Ogun waterside rural communities

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Conclusion

This study revealed the significance of wild edible species as a valuable source of indigenous vegetables that contribute to the dietary practices and sustainability of the local communities in Ogun Waterside. These species provide a means of local health care, addressing diverse food choices, nutritional gaps, and ethno-medicine in Ogun waterside, Southwestern Nigeria. The WEVs are integrated into the indigenous knowledge and habits of the area through the indigenous culinary dishes of the region. This study also provides valuable insights that can be harnessed to promote these plant species for wider utilization and encourage further studies on the nutritional assessment and potential toxicity of wild edible vegetables. This will help in identifying those species that may offer high nutrient quality, which can serve as functional foods, and avoiding those that may contain compounds which could pose health risks. Indigenous knowledge about plant use associated with various communities needs to be preserved for future generations to prevent knowledge erosion. It is important to prioritize the domestication of these wild edible species as a vital aspect of conservation and improving biocultural resilience.