Anatomical, histochemical and micrographic analysis of aerial parts of Aristolochia elegans Mast. (Aristolochiaceae), a potentially toxic plant used in folk medicine

Aristolochia elegans (Aristolochiaceae) is a plant species indigenous to South America, widely employed in traditional folk medicine and commonly referred to as 'mil hombres'. Despite its medicinal applications, this plant contains aristolochic acid; a compound associated with the potential risk of chronic intoxications and induced nephropathy following prolonged ingestion. The absence of comprehensive microscopic identification guidelines for A. elegans, whether utilizing fresh, dried, or powdered specimens, highlights the necessity to establish its pharmacognostic diagnostic characteristics ensuring the recognition of the species and its safe and controlled utilization.

Mild dissociations, transversal sections and electron microscopy observations were performed on specimens collected at the Costanera Sur Ecological Reserve and the Buenos Aires Botanical Garden (CABA). In addition, histochemical tests were conducted to asess the presence of primary and secondary metabolites.

The stems exhibited secondary growth, characterized by diffuse porous wood and 7–9 medullary rays. The xylem showed wide scalariform pitted vessel units and fibrotracheids. Whereas the leaves presented hooked trichomes and rodlet-shaped epicuticular wax deposits, a common trait among Aristolochia species. The histochemical analysis revealed the presence of alkaloids in the cortical parenchyma and fibers of the stems and petioles, as well as phenolic compounds in the xylem and cortical parenchyma of young stem and in the lamina mesophyll and abaxial epidermis adjacent to the midrib of the leaf. These micrographic described features serve as valuable tools for identifying A. elegans in commercial samples.