The pericarp structure and histogenesis in Enkianthus: on the ancestral fruit type in Ericaceae family

According to modern phylogenetic data, the monotypic subfamily Enkianthoideae is sister to all other subfamilies of the family Ericaceae s.l. Aiming to determine the peculiarities of development and structure of Enkianthus pericarp and to reveal the principal characters of its structure, which can be original for the Ericaceae, we have studied fruit anatomical structure at different stages of development in four species of the genus Enkianthus belonging to three sections: Meisteria, Enkiantella, Enkianthus. The pericarp of superior loculicidal capsule of Enkianthus is differentiated into three histogenetic zones: (i) one-layered exocarp, (ii) multilayered mesocarp differentiated into two histological zones: the peripheral parenchymatous one, and the inner sclerenchymatous one, and (iii) one-layered endocarp composed of tangentially elongated sclereids. It has been shown that the lignification of cells of the endocarp proceeds after the lignification of the inner zone of the mesocarp. Our investigation demonstrates that the superior loculicidal capsules of Enkianthus are capsules of Hamamelis type, which are recognized as the probable ancestral (plesiomorphic) fruit type for other subfamilies of Ericaceae. This fruit type is recognized as the original in several modes of morphogenetic transformations of fruit in Ericaceae family, from which other types of capsules, pyrenariums, and berries originated.