Banisteriopsis caapi (mariri), a member of the Malpighiaceae family, is a plant of great biocultural significance in the Amazon, used in the preparation of Ayahuasca tea in combination with Psychotria viridis. This study characterized the social knowledge network related to mariri, analyzed its ethnobotanical aspects, and investigated its genetic diversity in both native and cultivated populations. The social network analysis employed the Snowball Sampling technique and semi-structured interviews. The results, based on 24 interviewees from the União do Vegetal, demonstrated that knowledge transmission regarding species identification and management occurs within an institutional hierarchy that integrates ecological, cultural, and spiritual aspects in the Amazon rainforest. The ethnobotanical investigation revealed that 84% of respondents identified mariri by the presence of oil glands on the leaves, and 72% associated Ceiba pentandra (samaúma) as a companion plant to the vine. The study also highlighted the potential of agroforestry cultivation as a strategy for species conservation, reducing pressure on native populations.
Reproductive characterization analyzed five native and five cultivated individuals subjected to the acetolysis method to describe floral and pollen morphology, meiotic index evaluations, pollen viability, and cytochemical composition of pollen grains. Ideal floral buds for meiotic index analysis ranged from 1.74 to 2.28 mm in length. Cultivated individuals exhibited a higher percentage of normal post-meiotic products (91.95%)
compared to native individuals (83.86%). Pollen viability ranged from 72.48% to 94.64% in native populations and exceeded 95% in cultivated ones. Cytochemical tests confirmed the presence of starch and lipids as pollen grain reserve substances in all individuals. Genetic diversity analysis was conducted on native populations from Southern Amazonia, in the states of Mato Grosso and Rondônia, and in cultivated populations in Mato Grosso, using ISSR molecular markers. The study revealed 92.3% polymorphism, with an average of 11.55 bands amplified per primer and a mean PIC value of 0.4662, classified as moderately informative. Native populations exhibited higher genetic diversity (H = 0.3234; I = 0.4684) compared to cultivated populations (H = 0.1642; I = 0.2414), highlighting their importance as genetic reservoirs. AMOVA indicated that 57.98% of genetic variation occurs among populations, suggesting low gene flow (Nm = 0.4850) and strong genetic structuring (Fst = 0.5823), demonstrating that cultivated propagules originated from different sources than the studied native populations. The UPGMA dendrogram and Bayesian analysis revealed clustering patterns influenced by geographic isolation and human management practices. The results of this study reinforce the importance of conserving B. caapi native populations in the face of increasing Amazonian deforestation. They also underscore the role of these populations as essential genetic reservoirs for maintaining the species’ variability and diversity. Sustainable cultivation management is crucial to preventing genetic erosion and ensuring the preservation of genes associated with bioactive properties and ecological adaptation, safeguarding the continued traditional use of Ayahuasca by communities that rely on this ethnospecies.