Micromorphological and phytochemical insights on Phlomis fruticosa L. cultivated at the G.E. Ghirardi Botanical Garden (Lombardy, Northern Italy)

Glandular Trichomes and Essential Oils Variability in Species of the Genus Phlomis L.: A Review

“…The data available in the literature regarding the morphology of glandular trichomes in the Phlomis species are synthesized in Table 1 and Figure 1. Considering the morphological characters described by various authors [13,39,[42][43][44][45][46][47][48][49], we grouped the capitate trichomes into five categories (C1-C5) and the dendroid trichomes also into six categories (D1-D6). There is still variability in relation to these categories; the classification was made to simplify the description.…”

“…Type C2 is described by El-Banhawy and Al-Juhani [42] in P. aurea (distinct from type C1, consisting of short trichomes, but also from C3 or C4, because it has a single large glandular cell). Type C3 is described in P. aurea [42], P. herva-venti [46] and P. fruticosa [39] and has four large glandular cells.…”

“…The term "dendroid glandular trichome" was used by Nikolakaki and Christodoulakis [44], Yetişen [48], El-Banhawy, Al-Juhani [42] and Gostin [46]. These trichomes were also described as "compound glandular hairs" by Azizian and Cutler [13], "stellate type with glandular arms" by Çalı [49] and "branched stalked" by Giuliani [39]. We chose to use this terminology due to the fact that the nonsecretory part of the trichome is clearly dendroid, an accepted term for non-glandular trichomes in the same category [53].…”

“…Their role in the secretion of volatile oils has long been considered major within the family, some authors [33] considering species lacking peltate trichomes as not belonging to the category of aromatic plant species (for example, Prasium majus L.). However, the progress of research on the histochemistry of glandular trichomes indicated the presence of secretion consisting of essential oils in capitate and dendroid trichomes [39,46].…”

“…Sometimes, it can consist exclusively of hydrophilic compounds (as, for example, in some capitate trichomes from Salvia officinalis [28]), but in some cases (especially in species that do not present peltate trichomes), they can mainly secrete essential oils [38]. Besides the biological role of producing essential oils, glandular trichomes [39,40] (along with non-glandular ones) [41] have an important role in the taxonomic delimitation of species and genera from the Lamiaceae family.…”