Fruit anatomy and histogenesis in Mediterranean species of Arbutus (Ericaceae: Arbutoideae): ecological and morphogenetic aspects

Details of fruit anatomy and pericarp histogenesis were studied in Mediterranean species of Arbutus with the aim to determine the morphogenetic fruit type, to reveal the functional and ecological significance of fruit structure, and to suggest the most probable scenarios of fruit structural transformations in Arbutoideae (Ericaceae). The pericarp of the coenocarpous berries of Arbutus is differentiated into: one-layered exocarp, multilayered parenchymatous mesocarp with scattered solitary and groups of sclereids, and one-layered endocarp composed of thin-walled cells. The warts covering the fruit surface are formed by parenchymatous cells of the mesocarp and the exocarp. The process of pericarp development in Arbutus is divided into four periods, which correlate with the phenology and climatic factors of the Mediterranean region. The origin of the dormancy period in the middle part of fruit development in Arbutus is interpreted as an important adaptation to the arid Mediterranean climate. The data obtained suggest that both the berry of Arbutus and the pyrenariums of Arctostaphylos and Arctous are highly specialized fruit types that could not have derived from each other. The capsule of Hamamelis type of Enkianthoideae is recognized as the original fruit type of the berries and pyrenariums of Arbutoideae.