Insight into the structure and chemistry of glandular trichomes of Labiatae, with emphasis on subfamily Lamioideae

Glandular trichomes of Labiatae are among the most investigated secretory structures. Most species studied belong to subfamily Nepetoidae, including plants with aromatic properties, while so far a few species of subfamily Lamioideae were examined. In this work, we studied the micromorphology, ultrastructure, type and release of secretion of the glandular trichomes present on leaves and flowers of several species belonging to subfamily Lamioideae, (Stachys alopecuros (L.) Bentham subsp. alopecuros, S. officinalis (L.) Trevisan subsp. officinalis, S. germanica L. subsp. germanica, S. germanica L. subsp. salviifolia (Ten.) Gams, S. sylvatica L., S. heraclea All., S. plumosa Griseb., S. annua L., Prasium majus L., Sideritis romana L.) and one to the sister group Scutellarioideae (Scutellaria galericulata L.). Besides the well-known peltate and small capitate trichomes, widely described in the literature, other types of glandular trichomes were encountered; stalked peltate hairs and large capitate hairs. In particular, a new type of capitate trichome, exclusive of calices and corollas, which presents a mode and release of secretion never described before, is reported.