Impacts of urban environment on the leaves of two popular medicinal plants: Lippia alba (Mill.) N. E. Brown (Verbenaceae) and Coleus barbatus (Andrews) Benth. (Lamiaceae)

Previous studies have demonstrated that urban environmental conditions are sufficient to induce changes in leaf structure and alter the toxicological properties of leaf extracts from medicinal plants. The present study aimed to detect changes in the structure of leaves of Lippia alba (Mill.) N. E. Brown (Verbenaceae) and Coleus barbatus (Andrews) Benth. (Lamiaceae) induced by interactions with pollutants and abiotic factors in an urban environment. Control areas were used to compare the observed results. Leaves were processed according to standard techniques for plant anatomy, and a chemical analysis of the soil in the different study sites. For the external surface of the leaves, differences were observed in the stomatal density and the structure and density of tector and glandular trichomes. This study highlights the sensitivity/plasticity of secretory structures in a comparative way. The higher concentration of lead in the soil, the high levels of O3, high temperature, and lower levels of rainfall observed in the urban site may have influenced the variation in these anatomical characteristics. These aspects are essential for establishing best practice guidelines for using species for medicinal purposes.