Despite the difficulty in locating osmophores in the absence of morphological identity and inefficiency of neutral red staining, the osmophores of P. adamantinum have some features expected for these structures. The results indicate a functional link between thermogenesis and volatilization of osmophore secretions to produce olfactory signals for attracting specialized beetle pollinators. These first experimental data about the precise location of osmophores in Philodendron will stimulate studies in related species that will allow future comparison and the establishment of patterns of functional morphology.

Philodendron is the only genus of Araceae in which resin release occurs in the inflorescence. The resinous secretion adheres to the smooth body surface of the pollinating scarab beetles and allows attachment of pollen grains, making its transport possible. In order to understand the process of resin synthesis and release to the external environment, we used structural, ultrastructural and histochemical analyses at different stages of development of the inflorescences of Philodendron adamantinum. Two types of secretory canals were observed in the spathe: small caliber canals near the abaxial face, and larger caliber canals in the adaxial region. Only the latter canals release secretion into the external environment. The secretory epithelium in these canals is formed by a layer of cuneiform cells, and exhibits secretory activity throughout the development of the spathe. Resin exudation is a peculiar characteristic of these canals and appears to result from pressure exerted by the secretory epithelium and by structural modifications in the wall of cells adjacent to the epidermis, which allow the formation of a separation zone whereby the resin is released. The observed synchrony between anther dehiscence and resin exudation of P. adamantinum enhances the role of this secretion in the pollination process.

Extrafloral nectaries (EFNs) are involved in animal-plant interactions that lead to protection against herbivory. The presence of EFNs in Araceae is rare, besides Philodendron, there is report for only two other genera. With the aim to investigate the occurrence of EFNs in Philodendron and to describe the distribution patterns and structural organization of these glands, 75 Philodendron spp. were examined, 16 of which were selected for study by light microscopy. Three Homalomena spp. were also examined for EFNs, but these were not found. Philodendron martianum was employed as a model for additional study using scanning and transmission electron microscopy. The studied EFNs showed a high degree of structural similarity. They were present in the prophyll, leaf and spathe, becoming functional in young organs. In surface view, EFNs consisted of small areas and showed one or more stomata through which secretions were released. The secretory cells formed a globular region surrounded by ground parenchyma. In P. martianum, nectariferous parenchyma cells exhibited typical features of cells with high metabolism related to nectar secretion. These results allow us to infer that EFNs have a widespread occurrence in Philodendron, and they remain an exclusive character for this group.

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