Microscopic and Microchemical Characterization of Leaves and Stems of Acmella bellidioides

Acmella bellidioides (Asteraceae), commonly known as "arnica-do-campo", is a South American native medicinal plant mainly found in Brazil, Argentina, Uruguay and Paraguay. The indigenous people in these regions use the flowers of this plant to treat diseases of the digestive, musculoskeletal and sensory systems. Many Acmella species are morphologically similar, and there are a few anatomical studies available in the literature that can be used to identify and distinguish them. Several other members of Asteraceae, such as Calea uniflora, Chaptalia nutans, Porophyllum ruderale, Pseudobrickellia brasiliensis and Solidago chilensis, are also called "arnica-do-campo" or "arnica". Applying the same common name to several other species makes it difficult to identify the plant correctly and allows it to be more easily adulterated. The present study characterizes A. bellidioides using microscopy and microchemical techniques to provide pharmacobotanical data to support the authentication of the species. The notable anatomical markers identified in A. bellidioides are hypostomatic leaves, anomocytic stomata, peltate glandular trichomes on the leaf abaxial surface, midrib vascular system with three collateral bundles in an open arch, and the presence of prismatic crystals in the leaves and stems. These characteristics can help species identification and differentiation of A. bellidioides from other Acmella species and Asteraceae species known as arnica-do-campo.