Secretory structures in Aldama species (Heliantheae-Asteraceae): morphology, histochemistry and composition of essential oils

- Morphology and histochemistry of the secretory structures of Aldama were analyzed.
- A comparison of the essential oil constituents among the species was performed.
- Hydathodes, glandular trichomes, canals and cavities were identified.
- Essential oils are produced by glandular trichomes, canals and cavities.
- Essential oils from the same organs were more similar than from a given species.

Aldama representatives are particularly noteworthy for producing essential oils, and the chemical composition identification of these oils can help in the search for possible bioactive compounds, and provide useful information for taxonomic studies. A correct description of the occurrence and positioning of the secretory structures related to the production of these metabolites in the plant body could provide a basis for future studies on biological and pharmacological activity, indicating which organ merits further investigation. The four Aldama species investigated here were chosen due to their aromatic and resiniferous potential and because they are morphologically very similar. They were investigated phytochemically and their secretory structures were identified. Four types of secretory structures were found for the species herein: hydathodes, glandular trichomes, canals and cavities. Except for the hydathodes, all of them are responsible for the essential oil production. The highest yields of essential oils were obtained the underground organs. Seventy-nine compounds were identified for the four Aldama species, whereas 13 compounds occurred in the essential oils from all species and some of them were unique to a given species. The chemical composition of the four species, described herein for the first time, can be used for identification purposes and, also reveals several compounds of proven biological activity, confirming the potential usefulness of Aldama species.