Trichome Microscopy as a Diagnostic Tool for Species of the Solidago Complex: S. chilensis and S. microglossa

The plant species identification process is one of the most critical stages of quality control of plant raw material. Microscopy serves as the most accessible means for this purpose. Epidermal appendages, such as trichomes, are important botanical markers of plant drugs, taking into account their presence or absence and micromorphology. Trichomes are useful in detecting adulterants or substitutes and in authenticating plant raw materials. The genus Solidago includes two morphologically similar South American species, S. chilensis Meyen and S. microglossa DC. (syn. S. chilensis var. megapotamica). The two species belong to the "S. chilensis" complex and are commonly called arnica-do-mato or arnica. They are morphologically separated primarily on the basis of the average length of the non-glandular trichomes present in the stems. The objective of this study was to search for microscopic markers for the identification and differentiation of these two species to support species identification and quality control of the vegetable raw material. For this purpose, the usual techniques of light and scanning electron microscopy were used. Five types of trichomes were found in this study: I. Simple non-glandular trichome, II. Uniseriate non-glandular trichome, III. Biseriate non-glandular trichome, IV. Flagelliform glandular trichome, and V. Capitate glandular trichome. S. chilensis has simple non-glandular, flagelliform glandular, and rarely capitate glandular trichomes. Whereas, in addition to its glandular trichomes, S. microglossa has two types of non-glandular trichomes: biseriate and uniseriate. Thus, the two South American species of Solidago can be microscopically identified and differentiated based on the presence and absence of the characteristic trichomes. These differences can serve as pharmacognostic subsidies for quality control of the evaluated species.