Micromorphological and phytochemical insights on Phlomis fruticosa L. cultivated at the G.E. Ghirardi Botanical Garden (Lombardy, Northern Italy)

A multi-level study was performed on the vegetative and reproductive organs of Phlomis fruticosa L. (Lamiaceae), cultivated at the G.E. Ghirardi Botanical Garden (Toscolano Maderno, Brescia, Northen Italy). This work is part of the project Ghirardi Botanical Garden, factory of molecules…work in progress, intended to preserve and enhance the plant heritage hosted at the study site. The multidisciplinary research combined four approaches: I) micromorphological, to describe the structures responsible for the productivity of secondary metabolites; II) histochemical, to define the chemical nature of the secretory products by Light Microscopy, Fluorescence Microscopy, and Scanning Electron Microscopy; III) phytochemical, to characterize the Essential Oil obtained from the blooming aerial parts by hydrodistillation with a Clevenger-type apparatus, consequently analysed by Gas Chromatography-Mass Spectrometry; IV) biological, to assess the potential biological activity of the most abundant EO components based on literature data. Overall, P. fruticosa presented non-glandular and glandular trichomes. The former were multicellular stellate or simple uniseriate, the latter capitate belonging to three morphotypes: branched stalked with a one-celled head, simple short-stalked with a one(two)-celled head, simple medium-stalked with a four-celled head. For the first time, the histochemical survey reported digital images showing a predominant terpenes secretion by the branched-stalked and simple medium capitates, while the simple short hairs were responsible for the secretion of mucopolysaccharides and acid polysaccharides. The EO profile revealed 50 compounds and was dominated by sesquiterpene hydrocarbons (51.1 %) and oxygenated sesquiterpenes (33.6 %), with ar-curcumene (24.3 %), caryophyllene oxide (22.5 %) and α-cedrene (12.8 %) as most representative compounds. Finally, based on literature data, antimicrobial, antioxidant, and anti-inflammatory properties were hypothesized.

In the context of Open Science, an original iconographic apparatus was drafted based on these results to make them accessible to the visitors of the G.E. Ghirardi BG, as an opportunity to discover the plant heritage from an unusual perspective.