How symptom perception influences the selection of medicinal plants for the treatment of therapeutic targets in local medical systems

Understanding how people select medicinal plants in local medical systems is one of the central questions in Ethnobiology. Although characteristics of medicinal plant species, such as perceived efficacy, availability, organoleptic characteristics, among others, have been investigated, the influence of perceptions of therapeutic targets, particularly their symptoms, on this process remains poorly understood. We investigated whether therapeutic targets that share similar symptoms are treated with similar sets of medicinal plants, and whether this pattern is maintained for therapeutic targets perceived as recent in people’s daily lives within local medical systems, at both the community and individual levels. The study was conducted in two communities in Northeastern Brazil. We carried out free-listing exercises and semistructured interviews to document medicinal plants, therapeutic targets, associated symptoms, and people’s perceptions regarding the temporality of therapeutic targets. Similarity matrices based on Jaccard distance were constructed for symptoms and plant use. Bayesian mixed-effects models were fitted to test whether symptom similarity predicts similarity in plant use and whether this association is maintained or altered when at least one of the compared therapeutic targets is perceived as recent. At the community level, symptom similarity was positively associated with similarity in the use of medicinal plants, indicating that therapeutic targets with greater symptomatic overlap tend to share similar sets of plants. This association remained stable regardless of the presence of therapeutic targets perceived as recent. At the individual level, however, no consistent association was observed between symptom similarity and similarity in plant use, and recency did not moderate this relationship. The results suggest that local perceptions of disease symptoms may contribute to structuring plant selection at the community level, reflecting therapeutic patterns that likely emerged from individual experiences and were consolidated over time through social validation and cultural transmission. At the individual level, this pattern was not observed, suggesting that individuals participate in the construction of community knowledge but do not retain its full content; instead, they manage only part of the collective repertoire. This management of knowledge may be influenced by pathways of knowledge transmission, characteristics of therapeutic targets, and characteristics of the resources. These findings highlight the relevance of considering the dynamics of medicinal plant knowledge across different scales.