Micromorphology, ultrastructure and histochemical localisation of trichomes in Solanum mauritianum Scop. (Solanaceae)

Solanum mauritianum Scop., a densely pubescent member of the Solanaceae Juss., is widely invasive in South Africa and is also used ethnomedicinally. Despite its ecological significance and reported biological activities, the micromorphology, ultrastructure and phytochemical localisation of its trichomes have not been described. This study investigated the types, distribution, ultrastructural organisation and histochemical characteristics of trichomes in S. mauritianum using integrated microscopy. Leaves, stems and fruits were examined using stereomicroscopy and scanning electron microscopy (SEM) to document surface morphology and distribution, while light microscopy and transmission electron microscopy (TEM) were used to characterise trichome internal organisation and ultrastructure. Histochemical analyses were performed to localise major metabolite classes within trichome tissues. Microscopic investigations revealed a dense indumentum dominated by multicellular stellate non-glandular trichomes across all organs, with greater coverage on the abaxial leaf surface. Unicellular non-glandular and capitate glandular trichomes were additionally present but frequently obscured beneath the non-glandular canopy. Glandular heads exhibited smooth, grooved and collapsed morphologies, consistent with different secretory stages. Ultrastructural analyses revealed axial differentiation of the basal, stalk and multicellular head regions, with metabolically active cells containing prominent nuclei, chloroplasts, mitochondria and electron-dense inclusions. Histochemical staining demonstrated localisation of alkaloids, phenolics, terpenoid-related compounds, polysaccharides, lignified components, lipids, proteins and nucleic acids in both glandular and non-glandular trichomes. These findings provide the first integrated anatomical and histochemical account of trichomes in South African populations of S. mauritianum , suggesting that epidermal surface traits warrant experimental testing for potential roles in defence and stress tolerance within the introduced range.