Although extensively studied for its pharmaceutical properties, Teucrium polium has yet to disclose its leaf structure and the chemical nature of the accumulated or secreted products. Therefore, light, scanning, and transmission electron microscopy along with histochemical tests were employed to investigate the leaf of this perennial dwarf Mediterranean shrub. Structural characteristics include large cells with cutinized walls, creating cavities of obscured function in contact to a vessel element of the conductive tissue and different types of glandular hairs. A variety of secreted materials was identified by certain histochemical stains within the mesophyll cells and the glandular hairs. A dense indumentum of non-glandular hairs protects the secretory apparatus and the leaf surface from the stressful conditions of the Mediterranean climate.

Lippia citriodora H.B.K. is an aromatic plant indigenous to South America. It is cultivated and commercialised as an ornamental for its lemon-like scent emitted from its leaves and flowers. The present morphoanatomical and histochemical study revealed that leaves of L. citriodora possess one type of setae (non-glandular) and at least five types of glandular trichomes, with the latter differing anatomically and in the composition of their secondary metabolites. Scanning electron microscopy revealed that the same types of trichomes exist also on the calyces. Histochemical tests indicate that the glandular trichomes contain a combination of terpenoids, flavonoids, carbohydrates, phenolics and alkaloids. However, within the vacuoles of the mesophyll cells, terpenoids, phenolics, flavonoids and tannins are stored. The presence of lamellar cytoplasmic inclusions in the mesophyll cells, possibly precursors of tannins stored in the vacuoles, is reported for the first time. © 2010 CSIRO.