Anatomical, histochemical, and micromorphological aspects of leaf gall in Myrciaria floribunda H.West ex Willd. O. Berg (Myrtaceae)

Myrciaria floribunda (H.West ex Willd.) O. Berg (MYRTACEAE) is a galling superhost plant typical of restinga ecosystems. Among the morphotypes described for the species, the star-shaped gall has a differentiated morphology with leaf appendages. This study assessed the occurrence and characterized the structure of star galls in individuals of Myrciaria floribunda from the restinga de Jurubatiba National Park (Quissamã, RJ). Galled and non-galled leaves were collected from three individuals for morphoanatomical, micromorphological, and histochemical analyses. The formation of the star gall in M. floribunda causes numerous morphoanatomical changes resulting in a unique and very conspicuous structure. The gall is covered by simple epidermis and the ground system is formed by the hyperplasia and hypertrophy of the parenchyma and differentiation of a sclerenchymatous shell. The gall parenchyma is interspersed with vascular bundles. Protection mechanisms against predation are present such as leaf appendages covering the entire surface of the gall, sclerenchymatous shell, and phenolic and crystal idioblasts in the gall cortex. The absence of secretory structures in the gall cortex and their presence in the leaf appendages also points to a protective strategy. The starch and lipids reserves supply energy to the gall. Thus, the distribution of metabolites within the gall structure forms a histochemical gradient which represents a precise balance that ensures the development of the gall-inducer and prevents the action of predators. Anatomical analyses showed the complexity of the system and corroborate the premise that the gall constitutes a protective structure for the development of gallers.