Morphology and phytochemistry of Teucrium chamaedrys L. (Lamiaceae) cultivated at the Ghirardi Botanic Garden (Lombardy, Northern Italy)

Abstract Teucrium chamaedrys L. (Lamiaceae) cultivated at the Ghirardi Botanic Garden (Lombardy, Northern Italy) was studied through a four-level research approach: 1) micromorphological and 2) histochemical to describe the features of the glandular trichomes on the vegetative and reproductive organs and the chemical nature of their secretory products, by means of Light, Fluorescence and Scanning Electron Microscopy; 3) phytochemical, with the first characterization of the volatiles spontaneously emitted by leaves and flowers of samples of Italian origin by means of Head-Space Solid Phase Micro-Extraction (HS-SPME) coupled with Gas Chromatography–Mass Spectrometry (GC-MS); 4) ecological, through the combination of the morphological and phytochemical results with literature data concerning the ecology of the major volatile compounds. Three trichome morphotypes were observed, with a different distribution pattern on the vegetative and reproductive organs: peltates and short-stalked capitates, both ubiquitous on the whole plant, and long-stalked capitates, exclusive to the floral whorls. Both the peltates and the long-stalked capitates were recognized as the main sites of the terpene production. The HS-SPME analysis indicated that flowers displayed the most complex qualitative profile. Indeed, the vegetative and floral bouquets showed the predominance of sesquiterpene hydrocarbons and shared the main compounds, i.e., β-caryophyllene, γ-muurolene, and β-cubebene. From the literature data, a prevailing defensive action was highlighted both at the vegetative and reproductive organs level, along with the potential seductive role played by the floral bouquet.