Morphology and density of glandular trichomes of Ocimum campechianum and Ruellia nudiflora in contrasting light environments: A scanning electron microscopy study

Glandular trichome morphology and density may be of ecological importance since, in some plant species, they are strongly influenced by external factors such as temperature and light intensity. In this study, we describe the morphology and density of leaf glandular trichomes of Ocimum campechianum and Ruellia nudiflora plants growing under two different light environments (sun vs. shade) in order to determine whether there is an effect of light availability on trichome density in these plant species. The morphology and density of the glandular trichomes in both species were studied using scanning electron microscopy (SEM). Two morphologically distinct types of glandular trichomes were observed on O. campechianum leaf surfaces: peltate and capitate, of which the former was more abundant (ca. 3:1). In R. nudiflora, only one morphotype of peltate trichome was observed on both leaf surfaces. Overall, the trichome density of both species was higher on the abaxial than on the adaxial leaf surface. However, the plants exposed to full solar radiation and those in the shaded conditions presented similar glandular trichome densities (O. campechianum: sun = 16.7 vs. shade = 15.5 number of trichomes per mm−2; R. nudiflora: sun = 13.1 vs. shade = 11.9 number of trichomes per mm−2). Trichome density is therefore likely to be a fixed condition in the studied species.