† Background and Aims 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. † Methods 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. † Key Results 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. †Conclusions 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.

The genus Lippia Houst. (family Verbenaceae Juss.) has been used medicinally for centuries in various cultures. Numerous traditional medicinal applications of the South African Lippias are known, and among these is Lippia scaberrima Sond., the "Beukesbossie". Products recovered from L. scaberrima include essential oils by means of batch microwave distillation and a herbal tea manufactured by various methods. Microwave heating occurs through direct absorbtion of input energy. The whole sample is heated simultaneously with a heating rate much faster than for water distillation. Microwave distillation times can be expected to be less than corresponding water distillation times. A large number of parameters influence essential oil composition and yield. Various geographical, climatic, botanical, production and other parameters were identified and listed. The natural distribution of airdried leaves and flower heads and water as solvent was used in a domestic type microwave oven. Microwave distillation production parameters were studied and optima determined with respect to maximum oil yield. The batch microwave distillation production parameters studied (irradiation time, ratio of water used to plant material used, plant material moisture content, solvent recycling, physical size of plant material, addition of a surface tension modifier, soaking as pretreatment, load size, distillation kinetics and alternative solution medium namely ethanol) lead to a better understanding of microwave essential oil production. It enabled design of prototype continuous microwave distillation apparatus. Mobile, continuous microwave distillation equipment enables extraction of essential oils in a rural environment. It allows rapid investigation of a large variety of plants, and retrieval of essential oils in an economical and uncomplicated manner. Water distillation represents a classical technique for essential oil retrieval whereas microwave distillation is probably the most modern method. Physical and chemical properties of microwave and water distilled oils were determined. This enabled comparison of the microwave technique to a standard, industrially accepted production method. Tea was manufactured from L. scaberrima by means of the green tea, Rooibos tea and black tea methods as a first iteration in the production of a commercial tea. Drying curves was developed as well as appropriate regions of production variables like withering- and fermentation temperatures and times. / Dissertation (PhD(Ing.Chem))--University of Pretoria, 2002. / Chemical Engineering / unrestricted