Indigenous knowledge on Cochlospermum species
The findings in this study revealed that C. tinctorium and C. planchonii are well-known and identified by various names, meaning their importance for rural communities. Although vernacular names recorded showed an excess of monotypic taxa, it also revealed a polytypic diversity, e.g. Tchotcho'nda, Avokanfoun tchéké, Lissaya'nigou, as globally reported on medicinal plant [53]. In addition, the meanings of the vernacular names were exclusively descriptive and conveyed the traditional uses such as food (e.g. Boussorobu’nibou, Dissondi), therapeutic (Abuburoumey, Lissaya'nigou, Gbètou) or cultural (Tòòri, Tòòra) purposes. This emphasized previous findings positing that majority of folk nomenclatures of plants is mnemonics and reflects a broad spectrum of information on local uses, ecology, anatomy and several other aspects, which could differ greatly within peoples, areas and cultures [54–57]. Moreover, similarity was noted in vernacular names of different ethnic groups, e.g. Dendi and Zerma naming the both species as Kpata. This is likely due to the nearness of the two ethnic groups, on the point of view of geographical location, and also of their close relationship in history [58,59]. In the past, similar observations have been reported within two ethnic groups in Mexico having common ancestors who share cognate plant names in their pharmacopoeias [60].
Overall, 83 specific uses were recorded, grouped into ten categories, largely dominated by medicinal uses with 54 affections and symptoms treated, followed by food uses. The predominance of these two categories were previously reported for all the species of Cochlospermum genus [40] and specially for C. tinctorium and C. planchonii across the West Africa [24]. In addition, reporting the species as curing diseases such as malaria, hepatitis b and jaundice make them medicinally important plants, since malaria appears as the world's most important parasitic disease, with devastating consequences [61,62]. Moreover, although ten categories were recorded in this study, out of the fourteen reported by Johnson-Fulton [40], it was the first time the cosmetic use category was mentioned for Cochlospermum species. Conversely, horticulture, hunting, and gum categories were not documented in this study [40]. Our findings confirm the wide range of uses of Cochlospermum species across West African countries, such as Benin [23,63,64], Nigeria and Ivory Coast [65], Burkina Faso [66,67], and elsewhere [35]. In addition, as found in this study, literature review have highlighted gastro-intestinal and infectious as the most categories of affections treated by these species [24,40], and by this emphasized the good antibacterial evidence of Cochlospermum species [68,69].
Species availability and cultural use patterns
For their needs, local people sought different plant parts of Cochlospermum species, which abundance varied across the study areas. In fact, species abundance revealed Sudanian and Sudano-Guinean trends respectively for C. tinctorium and C. planchonii, reflecting likely their ecological affinity to semi-arid and arid regions [26,37]. Broadly, not only the rootstocks were the main organs sought for most of purposes but also showed an important commercial value, notably in the northern Benin [23,63]. Indeed, the trade of Cochlospermum rootstocks powder employs many women of various ages who practice this business as a principal or secondary activity. Year-round, and mainly after the crop harvest, women harvest, powder abundant rootstocks, and sell in in local markets, to enhance their household financial capacity. Although the economic importance of Cochlospermum species was scarcely documented, the trade around their rootstocks powder is highly helpful for rural populations, mainly in northern Benin [64]. Therefore, Cochlospermum species could be considered as good candidates for commercial production regarding their economic evidence [70,71].
As mentioned by informants, the Cochlospermum species were increasingly used not only because of their useful rootstocks, but also because of their availability year-round, even in dry seasons when most of plant resources are scarce and previous cropping are depleted [72]. Therefore, food uses are more accentuated to compensate for the lack or the expense of tomatoes and palm oil [64,73], thus increasing demand in the market. On the one hand, findings in this study revealed that people in northern Benin, where species were more abundant, used more the both species than these in center and south were species were less abundant. By that, the species abundance was correlated with their use values, supporting the resources availability hypothesis. This hypothesis have previously tested in different geographical areas in Africa [74] and elsewhere [5,12,14,75] to assess the close relationships between relative importance (measured by its use value) and a plant's local availability/abundance. On the other hand, it was also proved that ethnic groups were closely correlated with the use value of the both species, supporting the cultural importance in Cochlospermum species uses in Benin as reported for others plant species [49,76–78].
However, although both hypotheses of this study were confirmed, it is important to consider other factors that can considerably influence the analyses performed and the findings. If in the first time, if the use values of populations in the north were the most important, it can be due the very low purchasing power of most households in this region. Indeed, the populations of northern Benin are essentially rural and agricultural, and therefore have a relatively low financial capacity [33]. Thus, the high consumption of wild plants is not necessarily due to their local abundance, but rather to an alternative linked to the economic situation and therefore to low purchasing power. Moreover, the geographical location of the ethnic groups surveyed may also be an important factor. In this study, the ethnic groups with the highest use values were essentially located in the north part of Benin. Therefore, it appeared important to consider other factors in analysis performed for these hypotheses in order to enhance their veracity.
Implications for conservation
As reported in study, there is a growing concern about declining populations of Cochlospermum, as reported by the majority of informants. In fact, they considered conservation actions unnecessary, since both species regenerate naturally in the wild. Unfortunately, the harvesting mode adopted by several informants was to dig up and remove the rootstocks entirely. This practice causes killing the plant individual, and by that a considerable diminishing plant populations that likely lead to local extinction of the target species [79]. According to Leso et al. [80], these practices do not seem to ensure sustainable management and thus long-term availability of the species. As evidence, some harvesters confirmed having to go much further to harvest Cochlospermum plant parts, like the women of Banitè village (Malanville commune, located in Sudanian zone, at 11°52′00″N, 3°23′00″E), who are forced to rent cars (Fig. 7b) to collect large quantities rootstocks from neighboring localities.
Yet, some authors have already pointed out the overuse of Cochlospermum species for various purposes and underlined the pressure they are facing [79,81,82]. As posited, the high use value of plant species experiences them to a harvesting pressure [83], and hence the need for their sustainable management policies [20]. Therefore, if current economic, nutrient and cultural contribution of Cochlospermum species in rural populations’ well-being could be maintained and enhanced, sustainability approaches must be taken into account. Indeed, meeting sustainable management implies to overcome the current the needs without compromising the ability of future generations to meet their own needs [84]. A great challenge must be taken up in the context of a growing market demand for Cochlospermum root powder, leading to an increase in the quantities of roots harvested by the producers. In addition, there is a strong anthropic pressure linked to several causes of vegetation degradation of which deforestation, fire as a tool for hunting, and clearing for installing new or extending existing agricultural lands [85]. Several progress have made it possible to lead people to free oneself with wild food owing to agricultural expansion; nevertheless, this strongly contributes to ecosystem degradation and biodiversity loss [22].
Although rural populations are sometimes pioneers in the domestication process [64], no seeding or assisted natural regeneration were practiced by informants in this study. However, producers affirmed they will welcome any initiative of large-scale reproduction of the target species, so that to have much-more amount Cochlospermum rootstocks. Therefore, future investigations are needed on the impact of harvesting on the regeneration capacity of rootstocks, the biomass of rootstocks produced over a period of time, and the impact of harvesting on the population dynamics of these species. In addition, given the important economic, cultural and diet roles of Cochlospermum species, and the threats they are faced, they need to be considered within the priority species for conservation issues [49,70]. For the time being, existing conservation actions, including fallowing of harvesting areas, partial harvest are needed to be extended, and promoted these currently absent such as seedling, assisted natural regeneration, and weed protection.
Furthermore, in the context of species conservation, the assessment of species diversity remains one of the major and key steps in conservation biology [86,87]. Although diversity within the genus Cochlospermum in Benin is not yet elucidated, this study prioritizes the assessment of use patterns and local management of two well-known species, namely C. planchonii and C. tinctorium, to provide tangible data for their sustainable management [86]. In addition, morphological variations were noted in the collected vouchers of Cochlospermum species in this study. Therefore, it will be very interesting to determine the boundaries of Cochlospermum species based on morphological and reproductive variations [24]. The findings of this study will undoubtedly be of great value in filling the current gaps in species diversity within the West African genus Cochlospermum and thus contribute to improving biodiversity countrywide and in the Sub-Saharan region [88].