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

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.

先前被认为是叶栖穴（domatia）的结构，实则为产自巴西稀树草原的漆树科（Anacardiaceae）物种Anacardium humile叶片上的花外蜜腺（extrafloral nectaries, EFNs）。该类结构因与觅食蚂蚁存在关联，曾被描述为叶栖穴。然而蚂蚁会在叶片上采集分泌物，这一现象促使我们对该结构展开解析。为此，我们对这些疑似叶栖穴的结构的分布、微观形态、解剖特征及组织化学特性进行了系统分析。该结构位于较粗叶脉的叶腋处，由可分泌葡萄糖的腺毛组成，因此本文将其界定为花外蜜腺（extrafloral nectaries, EFNs）。泌蜜腺毛在幼叶上与其他表皮细胞处于同一平面，而在成熟叶片中则位于叶片表面的凹陷处。花外蜜腺的分泌活性仅局限于幼叶阶段，在成熟叶片中会发生退化。在其分泌的分泌物中可检测到碳水化合物与亲脂性化合物。综上，在叶片上觅食并采集花外蜜腺分泌物的蚂蚁，与该植物形成了互利共生关系：植物为蚂蚁提供糖类资源，作为回报，蚂蚁会保护植物免受植食性动物侵害，这一互作关系在处于发育阶段的叶片中尤为显著。