Anatomy and essential oils from aerial organs in three species of Aldama (Asteraceae-Heliantheae) that have a difficult delimitation

Recently, molecular analysis caused the South American Viguiera Kunth species to be transferred to Aldama La Llave. However, the circumscription has not been established for certain of the South American species, including Aldama filifolia (Sch. Bip. ex Baker) E. E. Schill. & Panero, A. linearifolia (Chodat) E. E. Schill. & Panero and A. trichophylla (Dusen) Magenta (comb. nov.), which had previously been treated as synonyms because of their high similarity. Therefore, the present study aimed to evaluate the anatomy of the aerial organs, and the yield and chemical composition of the essential oils from these three species, to determine the differences among them and thereby assist in species distinction. The anatomical analysis identified characteristics unique to each species, which are primarily related to the position and occurrence of secretory structures. Histochemical analysis demonstrated that the glandular trichomes and the canals secrete lipophilic substances, which are characterised by the presence of essential oils. The analysis of these essential oils identified monoterpenes as their major constituent and allowed for the recognition of chemical markers for each species. The anatomical and chemical characteristics identified by the present study confirmed that the studied samples belong to three distinct taxa.