An investigation of the glandular and non-glandular foliar trichomes of Orthosiphon labiatus N.E.Br. [Lamiaceae]

Using a combination of light (stereo and compound) and scaning electron microscopy, this study investigates the distribution and morphology of foliar trichomes of Orthosiphon labiatus (Lamiaceae) at different stages of leaf development. Three types of trichomes were observed: two glandular types (large peltate and small capitate) and one non-glandular type. Results revealed that the development of peltate trichomes was initiated in the early stages of leaf development. However, a higher number of developed peltate trichomes was observed in mature leaves, indicating an increase with age. Capitate trichomes are, by contrast, rare and sparsely distributed on both leaf surfaces. The highest density of non-glandular trichomes was observed on the abaxial leaf surface, especially along the veins, with the density decreasing with leaf maturity. This paper contributes towards the body of knowledge being assembled on the family Lamiaceae as it manifests in southern Africa.