Morphology and Histochemistry of the Glandular Trichomes of Lippia scaberrima (Verbenaceae)

Lippia scaberrima, an aromatic indigenous South African plant, with medicinal application, potentially has economic value. The production of essential oil from this plant has not been optimized, and this study of the chemico-morphological characteristics was aimed at determining the location of oil production within the plant. Furthermore, the locality of other secondary metabolites important in medicinal applications needed to be ascertained. This information would be useful in deciding the protocol required for isolation of such compounds. The morphology of the glandular trichomes was investigated using a combination of scanning electron and light microscopy. Concurrently, the chemical content was studied by applying various chemical reagents and fluorescence microscopy. Three types of trichomes were distinguished on the material investigated. Large, bulbous peltate glands containing compounds of terpenoid nature are probably the main site of essential oil accumulation. Small glands were found to be both peltate and capitate and fluorescent stain indicated the possible presence of phenolic compounds. The third type was a slender tapered seta with an ornamented surface and uniseriate base, and evidently secretory in nature. This study linking the chemical content and morphology of the glandular trichomes of L. scaberrima has contributed to the knowledge and understanding of secretory structures of Lippia spp. in general.