Botanicheskii Zhurnal, Vol 109, No 10 (2024)

We investigated glandular trichomes located on leaves and flowers of three Pelargonium (Geraniaceae) species: P. odoratissimum , P. exstipulatum and P. vitifolium . The aim of our research was to study the morphology and anatomy of the secretory structures located on aboveground parts of these plants, to specify their localization and frequency of occurrence, and to identify interspecific differences in their structure and distribution. The plant material was collected from greenhouses of the Komarov Botanical Institute RAS and examined using the methods of light microscopy and scanning electron microscopy. Glandular trichomes and simple hairs occur on the surface of leaves and flower elements. The glandular trichomes are the most frequent on the leaves of P. odoratissimum . According to our data, there is no de novo formation of trichomes during the leaf elongation. Five morphological types of glandular trichomes were described. Most of them are uniseriate and capitate (except for the third and fifth types). The trichomes of the third type are straight, while the trichomes of the fifth type are biseriate. The first type is the most frequent, as it can be found on the surface of all organs in every of the investigated species. The trichomes of the first and the third types can form a subcuticular secretory cavity. We have also revealed a unique fifth type of glandular trichomes with a multiseriate stalk that was not described before. The length of glandular trichomes can vary widely (especially in the second type), and the diameter of the secretory cell is a stable character within each morphological type. The largest diversity of trichomes is found in P. exstipulatum , the least in P. vitifolium . We also described interspecific differences in the morphology and localization of certain trichome types. This feature can be used for taxonomical purposes.