The "black nodules" of Hypericum perforatum L. subsp perforatum: Morphological, anatomical, and histochemical studies during the course of ontogenesis

Hypericum perforatum L., traditionally used in folk medicine as a therapeut ic plant, is today investigated for its antidepressant and antiretroviral a ctivities. This species is characterized by the presence of different types of secretory structures: translucent glands or cavities, black nodules, an d secretory canals. The aim of the present work is to characterize the blac k nodules on both the floral and vegetative parts, morphologically, anatomi cally, and histochemically. Nodules consist of a cluster of irregularly sha ped cells surrounded by a single- or double-layered sheath. Histochemical t ests show that the nodules are negative for the presence of lipids, essenti al oils, sesquiterpene lactones, steroids, and proteins and positive for pe ctic-like substances, tannins, and alkaloids. Our results show that the inf lorescences are richest in nodules and are, therefore, the best sites for t he extraction of the secondary metabolites.