Diversification hypothesis in therapeutic targets with physical and spiritual causes

In the current context of Morrinhos, the diversification hypothesis [4] does not seem to explain the role of exotic species in the local medical system. At this point, it is also important to question the definition of the biogeographic origin of the species, since the very classification of a species as “exotic” can be influenced by political and cultural factors [42]. Therefore, in future studies on the interaction between people and plants, especially when evaluating the influence of the origin and role of plants in LMS, it is important to take into account not only etic criteria determined by the interpretation of the researchers, but also the emic perception of the people involved, how they understand the introduction of the species in their therapeutic demands, and how they perceive a resource as “exotic” and “native” in their environment, without the biases of the associated political, cultural and environmental circumstances. As an example, in French Guiana, a recent study explored the emic view of quilombolas in relation to invasive exotic tree species and highlighted that these peoples often consider these plants as native to their socio-ecological systems, making etic definitions of little significance for them [43].

A systematic analysis of the diversification hypothesis in Brazilian biomes at different levels (national, regional and local) conducted by Medeiros et al. [44] revealed disparities between the main Brazilian ecosystems, from small differences to considerable overlap between native and exotic plants (p > 0.05), suggesting weaknesses in this hypothesis depending on the scope of the analysis. In Ecuador, introduced plants were more likely to be used to treat diseases with fewer native plant treatment options and to fill therapeutic gaps, lending support to the central idea of the diversification hypothesis [12]. However, cultural and environmental differences need to be taken into consideration when we compare these results [8], since the very understanding of what constitutes an illness can vary from place to place [11].

In this sense, in agreement with the literature, the incorporation of exotic plants aimed at targets already well covered by native species may represent an adaptive strategy of local communities to enhance the resilience of their medical systems, increasing the utilitarian redundancy and, consequently, the flexibility of alternatives, in addition to serving as a buffering mechanism against possible environmental disturbances that may compromise one or more species [15, 19]. The ability of the system to respond to disturbances is thus enhanced, ensuring the continuity of healing practices, whether physical or spiritual, by human groups. Furthermore, it is noted that human groups tend to incorporate plants into their medical systems not to favor redundancy in a large number of therapeutic targets, but rather in a particular set of targets locally considered the most important, thus suggesting that the inclusion of plants into LMS, regardless of the biogeographic origin of the resources, follows the logic of protecting specific therapeutic targets.

In line with this idea, studies carried out in rural communities in the semiarid region of Ceará found that the more redundant therapeutic targets were the most common and least severe, since the participants concentrated their efforts in gaining knowledge in events that were more likely to occur, promoting the resilience of the system [45, 46]. We understand that investing in strategies to increase redundancy in targets that rarely affect people is costly and unsafe, as the frequency of disease onset in the environment can be so low that the memorization of resources becomes difficult, compromising their use when necessary and the persistence of this information in time and space.

Experiments on adaptive memory and the evolution of the human mind in the context of medicinal plants found that people tend to remember more easily plants associated with common and less serious health problems [47]. This mnemonic capacity associated with these diseases can be explained by the high frequency with which they occur and by previous personal experiences, which facilitates the process of remembering therapeutic information [47]. Following this reasoning, we may look into the possibility that the diversity of plants in the most redundant therapeutic targets may have been favored by the recall of several species that treat the most common diseases of physical and spiritual nature, regardless of their origin, while non-overlapping and/or little redundant targets were affected by the lower retention of data in memory, possibly due to less frequent indications in the community.

Versatility in therapeutic targets with physical and spiritual causes

The therapeutic versatility of exotic and native resources was similar in the two groups of illnesses studied, contrary to what was initially proposed in the definition of the versatility hypothesis by Bennet and Prance [10]. Our findings differ from those of Hart et al. [12] in the Ecuadorian medicinal flora, in which greater therapeutic versatility was found for exotic species. Hart et al. [12] attributed this finding to the fact that the wide geographical distribution of exotic species, which were generally cosmopolitan, increased the chances of use, expanding discoveries and therapeutic possibilities, leading to the selection of exotic species based on their versatility. However, this same premise was not validated in other scenarios with drier conditions. In the semiarid region of Pernambuco, Alencar et al. [6] found that native plants were more versatile in general uses, with no significant differences between native and exotic plants in terms of therapeutic versatility. Likewise, no significant differences were found between native and exotic species in the Cerrado of Minas Gerais [8]. And in the present study, no differences were found either. Thus, the selection of exotic species in these systems, although geographically and culturally different, is not supported by the variety of therapeutic indications.

In these circumstances, we may consider the possibility that the differences observed in the studies may be associated with seasonality patterns in ecosystems and the way people have evolutionarily incorporated plants in the construction of their medical systems over time. In Ecuadorian ecosystems, seasonality is less pronounced [12] and does not play an important role as in Caatinga and Cerrado. The annual availability of plant resources is not a limitation for plant use patterns in the same way as in drier environments, where the temporary availability of many plants leads to greater attention and use of specific resources, such as woody species and their perennial parts, such as roots and bark [4, 48]. In addition, in past times, droughts in semiarid regions limited the access to water, posing difficulties to the management of several plant species, especially exotic plants in these areas.

Based on the assumptions presented above, the resources most likely to be found and used throughout the year in drier ecosystems, such as woody species and their permanent parts, have particularities that favor their frequent use, promoting experimentation and maximization of therapeutic benefits in local populations [49]. This may lead to the valorization of certain native species over time and consequent discovery of a variety of therapeutic functions, contributing to their versatility in relation to ephemeral species, including many exotic herbaceous species. This probably does not apply to Ecuadorian ecosystems. Thus, we believe that these factors have influenced the discovery of therapeutic properties of native plants and, thus, their versatility in drier environments. However, the advent of improvements in access to water for various purposes, including the cultivation and facilitation of the use of many exotic species, is a factor to be taken into account. Such improvements and issues related to seasonality together may have contributed to the variety of therapeutic indications and, thus, the similarity observed in terms of versatility between native and exotic plants in the present study. In this study, for example, we observed that most of the exotic plants mentioned by the participants were herbaceous species generally with a restricted distribution in the environment because of climatic seasonality or kept in backyards under human management and care, while native species consisted mostly of arboreal plants.

Plants with a wide range of medicinal applications have particularities that favor their selection by human groups [6]. In the Morrinhos community analyzed in this study, rue (R. graveolens), a plant native to the Mediterranean area and Southwest Asia [50], stood out with high versatility in therapeutic targets with physical and spiritual causes. Several ethnobotanical works have reported the use of this species for physical and spiritual purposes [21, 30, 31]. These results demonstrate that the same plant resources can satisfy targets of different natures in a therapeutic continuum that involves physical and magical aspects. The experimentation and inclusion of these plants may follow a similar dynamic in both contexts, with their therapeutic functions intertwining in the promotion of personal well-being.

Utilitarian redundancy and prioritization in therapeutic targets with physical and spiritual causes

Two scenarios were found regarding the prioritization of resources in the evaluated targets: exotic plants were prioritized in diseases of physical nature and native plants were prioritized in those of spiritual nature. To explain these differences, we propose two main influencing factors, according to the context analyzed: 1) the current ease of access to exotic plants, which are usually grown in home gardens and backyards, favoring their frequent use to treat physical diseases; 2) and the more intense connection between historical-cultural factors and spiritual problems, creating a certain resistance to the prioritization of redundant exotic resources, at least in the short term; people prefer to use native plants that have played a magical-religious role over generations.

In recent decades, public policies have affected the access to water in the Brazilian semiarid region, including the implementation of water supply systems through artesian wells and the adoption of cisterns and other reservoirs to collect rainwater, and this has contributed enormously to the reconfiguration and diversification of the water use pattern [51]. These measures have not only mitigated the effects of droughts, but also enabled and/or facilitated the maintenance of backyards and the cultivation of plants for subsistence [52], including medicinal species and, among them, many exotic plants whose cultivation would not otherwise be feasible. Thus, several exotic medicinal species are grown in backyards in the Northeastern semiarid region of Brazil [1, 53, 54], and this proximity with these plants may influence the choice of medicinal elements. In decision making, the perception of availability of plants can be influenced by their accessibility [55], since an abundant species can be perceived as unavailable if it occurs far from homes [56].

Environmental degradation caused by human activities is a critical factor that reduces the availability of forests for plant collection, implying greater time and effort required to obtain native plants [57]. At the same time, and in line with the ecological appearance hypothesis [4], local exotic plants in the current scenario, especially those grown and kept in domestic backyards at the service of people, in this case, consumers, end up becoming the most “apparent” in the community, that is, the most likely of being found and collected [56]. The reduction and distance of native forests, therefore, may have influenced the prioritization and consumption of exotic resources. This complex dynamics among access to water, plant use, and environmental changes can be fundamental to understand the choices of resources to treat physical diseases in semiarid communities such as Morrinhos.

Due to their multifunctionality, local backyards can work as therapeutic reservoirs and their medicinal resources tend to be prioritized, a trend that may also be present in other communities with similar conditions. In turn, this prioritization can bring benefits to the system from an adaptive and also environmental point of view, since the use-pressure concentrated on exotic resources somehow minimizes the impact on native species with redundant indications, ultimately contributing to their preservation [18, 19], besides maintaining local functions, and favoring the resilience of the system [14].

On the other hand, several exotic plants are often portrayed as species with high invasive potential, constituting the second largest threat to biodiversity [43] and bringing a negative impact on the conservation of native species [58]. However, in areas of dry forests, such as Caatinga, many exotic species only persist in favorable environments, such as backyards, due to human intervention, through management and care in their cultivation [20, 40], because most of them are unable to propagate and survive in areas of dry native forest, thus reducing the risks of invasion and the subsequent ecological impacts [59].

In the light of biocultural adaptation, Gama et al. [20] report that in certain environmental contexts there is a tendency for introduced plants to offer advantages over native ones due to the perception of greater therapeutic efficacy, palatability and availability. Yet the authors point out that, despite the advantages, these species only stand out in LMS when the cost–benefit ratio is favorable. Therefore, extrapolating this idea to our data, we can assume that many exotic species used to treat diseases of physical nature are not only the “most accessible” under current conditions, but also have a favorable cost–benefit ratio. These results show the dynamicity of culture and how socio-environmental variations can influence use patterns and prioritization within the system.

With regard to the prioritization of native plants for spiritual purposes, a plausible explanation may be the strong cultural attachment to these plants. Social and cultural factors can influence the selection process and use patterns [4]. Among plants with magical-religious use, we can infer that some native plants play the role of key cultural species in this context, whose existence in the community and intrinsic spiritual value are fundamental to the stability of spiritual therapeutic practices over time, given their symbolic and ritualistic role [60] and cultural prestige in the collective opinion that is difficult to replace [61]. Based on the concept of cultural keystone species, Tareau et al. [62] developed the definition of “spiritual keystone species” in reference to this symbolic, magical and spiritual centrality of certain species in magico-religious practices. In this study based on Neotropical cosmovisions, the authors highlighted the Amazonian tree Ceiba pentandra (L.) Gaertn (Malvaceae) as a significant “spiritual keystone species” in indigenous and Afro-descendant communities across America [62]. So, species of the native flora can play a very relevant role in the local cultural identity [61], especially when it comes to spiritual matters.

In line with the above, Bussmann and Sharon [63] found that most of the plants used in the treatment of magical/ritual ailments in Northern Peru come from mountainous forests of the Andes, especially those found in the vicinity of sacred sites, as they are considered more powerful and energetic and tend, thus, to be the most used in the Andean culture. Similarly, local communities in India believe that local trees play a central role in magical-religious processes, so that they maintain the knowledge and a close relationship with these native resources [64].

In a rural region of the Brazilian Amazon, Kawa [30] observed that species native to the Brazilian territory, such as J. gossypiifolia (“pinhão-roxo”), were the magical-religious plants most cultivated in the backyards for spiritual ailments. In rural backyards of South-Central Piauí, native species were the most cultivated for this purpose, especially J. gossypiifolia and Melocactus zehntneri (Britton & Rose) Luetzelb. (Cactaceae) [31]. The deliberate management of these species seems to be related to the preference of the maintainers for these plants, the greater confidence in their magical-religious efficiency, and the cultural link with these resources compared to other species, such as many exotic species used for similar purposes. In a study with prayers in Maranhão, Rabelo, Araújo and Almeida Júnior [65] did not find exclusivity in the use of magical-religious plants, but perceived a clear preference for two native plants (J. gossypiifolia and Scoparia dulcis L.—Plantaginaceae) due to the perception of their mystical efficiency and because of the greater cultural affinity with them.

Based on the above, the preference for certain magical-religious plants in the treatment of spiritual ailments permeates symbolic phenomena and is intrinsically linked to the cultural formation of each human group, as well as to their cosmovisions, identities, and empirical perceptions. In the context of this immateriality, it is believed that the cultural proximity of “sertanejo” human groups (inhabitants of the Northeastern semiarid region), such as the residents of Morrinhos, with native plants generates a more intense socio-cultural connection with these resources. Thus, the relationship between plants, the cultural context, and the identity of each group can be understood as playing a relevant role in the perception and appreciation of magical-religious resources in the context of ailments with spiritual causes.

Within the scope of this discussion, it is also important to highlight that some publications [66, 67] suggest that the use of plants in certain spiritual treatments, such as in rituals that involve direct contact with the patient’s body, can be based not only on magical properties attributed to these plants, but also on their active ingredients. In this sense, another challenging task pointed by Pagani, Santos and Rodrigues [68] is establishing a correspondence between the emic terms of traditional medicine and the symptoms or diseases known by conventional medicine. The authors demonstrated that some Culture-Bound Syndromes (CBS) resemble physical illnesses more than others. Therefore, in CBS in which there is a strong connection with the local belief system and cosmovision, it can be challenging to accurately discern the boundaries between magical and physical or between scientific and spiritual [21].

It is noteworthy that the priority given to native plants for magical-religious purposes may eventually create or intensify risks to these species. The family Cactaceae has a considerable number of species endemic to the Northeastern semiarid region of Brazil, such as Melocactus spp., among others, which are used in various ways in the “sertaneja” culture, including for magical-religious purposes [31, 69,70,71], as observed in the present work. Thus, the use-pressure on these resources can pose or aggravate threats to their diversity. This is especially true in the case of certain cacti of the genus Melocactus Link & Otto which occur mainly in Bahia and already appear as Critically Endangered (CR) or in other statuses of concern in the National List of Endangered Species [72]. The main threat to populations of these succulent plants comes from the extraction for commercialization in open markets and highways, intended for various forms of use [73]. Cultural factors and the additional uses of these plants for spiritual ends may affect the trade dynamics and extraction may be intensified. This reinforces the need for sustainable actions to preserve these plants and highlights that the involvement of local communities and the respect for their traditional knowledge are essential to ensure that magical-religious processes coexist harmoniously with environmental preservation.