Presumed domatia are actually extrafloral nectaries on leaves of Anacardium humile (Anacardiaceae)

Abstract

Presumed domatia are actually extrafloral nectaries on leaves ofAnacardium humile (Anacardiaceae), a species from the Brazilian savannah, is associated with foraging ants, which leads to the description of the structure of its leaves as domatia. However, the ants collect secretions on the leaves, a phenomenon that inspired us to elucidate this structure. To this end, we conducted an analysis of the distribution, micromorphology, anatomy and histochemistry of these supposed domatia. They are located in the axil of thicker leaf veins and are composed of glandular trichomes which exude glucose; they are, therefore, described here as extrafloral nectaries (EFNs). The nectariferous trichomes are located at the same level as the other epidermal cells on young leaves, while in mature leaves they were found in depressions of the leaf blade. The secretory activity of EFNs is limited to juvenile phases, becoming degenerated in mature leaves. Carbohydrates and lipophilic compounds were detected in the produced secretion. It can be concluded that the presence of ants foraging leaves to collect from EFNs indicates a mutualistic interaction, with the plant providing a sugar resource to the ants in return for protection against herbivory since they are present in developing leaves.