Palynological study of Erythroxylum (Erythroxylaceae): discrimination of species of forensic/criminological interest under light microscopy

The genus Erythroxylum comprises numerous species of significant ecological, ethnobotanical, and forensic relevance. Some species, such as E. coca and E. novogranatense, are widely known for their use in illicit cocaine production, while others play important roles in traditional medicine in the Neotropics and in maintaining biodiversity in tropical ecosystems. Due to their diversity and value, reliable tools for species identification are essential, especially in legal and conservation contexts.This study investigates whether pollen morphology and morphometry can accurately differentiate Erythroxylum species. Pollen grains from fourteen species were processed using acetolysis and analysed under light microscopy (measuring 17 quantitative and 14 qualitative variables), aimed at maximising comparability with environmental samples (from forensic or palaeoscience research). Morphometric results reveal notable structural conservation in pollen grains within the genus, with shared traits that hinder species-level identification. However, certain morphological characteristics, such as pollen shape, aperture structure, and exine thickness, provide clues to distinguish some taxa. From a forensic perspective, confidently differentiating E. coca and E. novogranatense from each other and from other species of the genus based solely on pollen under light microscopy remains challenging, but a dichotomous key based on a conservative threshold of mostly qualitative variables allows distinguishing the species studied.Multidisciplinary approaches integrating morphology, molecular, and chemical data are recommended to improve taxonomy, forensic traceability, and conservation strategies for Erythroxylum.