MICROMORPHOLOGY AND HISTOCHEMISTRY OF LEONOTIS LEONURUS L. TRICHOMES

Leonotis leonurus (Lamiaceae) (Wild dagga/Lion’s ear) is an important medicinal plant known for its psychoactive and medicinal properties and used to treat several ailments such as fever, influenza, asthma, epilepsy, snakebite, tapeworm, and skin diseases. Various biological activities, including antifungal, antibacterial, antiprotozoal, anti-inflammatory effects, and modulation of immune cell functions, are exhibited by extracts and isolated compounds from L. leonurus. The purpose of this study was to examine the micromorphology, distribution, and chemical composition of the bioactive compounds in the trichomes of L. leonurus, using light and electron microscopy, along with histochemical analysis. Stereomicroscopy and scanning electron microscopy (SEM) revealed the presence of both glandular and non-glandular trichomes on the leaves and stems. The presence of peltate glandular trichomes, morphologically distinct glandular capitate trichome types (type I and II), and uniseriate, multicellular (two to five cells) pointed-shaped non-glandular trichomes were revealed using histochemistry and SEM. Trichomes on the stained leaves and stems revealed phenolics and alkaloids as the primary medicinal compounds. Secondary metabolites are essential for defense against herbivory, inhibiting and repelling microorganisms, and may also possess medicinal properties. To the best of our knowledge, this study offers updated insights into the key micromorphological characteristics of the secretory structures on the leaves and stems of L. leonurus, along with preliminary information on the composition of the secretions produced by these trichomes.