The indumentum of the lamina of Pelargonium scabrum L'Herit. consists of only two types of trichomes, i.e. five-celled glandular hairs which produce essential oils and unicellular spiny hairs which are basally surrounded by enlarged epidermal cells. Every glandular hair consists of a globular head, three stalk cells and a characteristically elongated basal cell. Both glandular and spiny hairs develop by enlargement and/or division of a single epidermal cell. Ontogenetic studies have indicated that the different morphological types of glandular hairs in P. scabrum represent different developmental stages of a single glandular hair type. Secretion of essential oils apparently occurs repeatedly form the young five-celled stage, as a new cuticle develops underneath the ruptured one.
