Teucrium fruticans L., a Multi-Scale Study: From Trichomes to Essential Oil

This work represents the first multi-scale study on Teucrium fruticans L. cultivated at the Ghirardi Botanic Garden (Lombardy, Northern Italy), combining a micromorphological and a phytochemical survey on the plant's aerial parts. Micromorphological investigations, performed by Light Microscopy, Fluorescence Microscopy and Scanning Electron Microscopy, highlighted the presence of five trichomes morphotypes, distinguished by a different distribution pattern: peltates, short-stalked and ball-like medium-stalked capitates, ubiquitous on the whole plant, medium-stalked and long-stalked capitates, exclusive to the floral whorls. Both peltates and medium-stalked capitates were recognized as the main terpene production sites. Phytochemical characterization focused on the essential oils (EOs), obtained by Clevenger-type hydrodistillation in February and April 2022 and characterized by Gas Chromatography-Mass Spectrometry (GC/MS), which resulted mainly formed by sesquiterpene hydrocarbons. The February EO profile was characterized by β-caryophyllene (28.30 %) and germacrene D (19.16 %) as main compounds, while in April β-myrcene was detected at high percentage (13.77 %), in addition to the previous two components (15.72 % and 11.55 %, respectively). Literature data, dealing with the biological activities of the main oil constituents, highlighted an anti-microbial, anti-inflammatory, and anti-tumor potential, due to the high content in sesquiterpenes and, particularly, of β-caryophyllene and germacrene D.