Gynoecium and fruit histology, structure and development in corky-warted representatives of Livistoninae (Trachycarpeae: Coryphoideae: Arecaceae)

Representatives of three genera of Livistoninae (Johannesteijsmannia, Licuala and Pholidocarpus) develop corky-warted fruits in contrast to fruit with smooth surfaces in most other representatives of the 'apocarpous clade' of Arecaceae subfamily Coryphoideae. The present developmental study is focused on revealing the anatomical peculiarities of the fruit structure of corky-warted species of Livistoninae and tracing the development of their pericarp. Our study shows that the fruits of Johannesteijsmannia, Licuala bintulensis and Pholidocarpus macrocarpus are drupes of the Rhapis type and that the warts on their fruit surface originate soon after gynoecium pollination as the result of two or three developmental events: (1) suberinization of the exocarp cells; (2) progressive multiplication and growth of the outer zone of the mesocarp; and (3) cracking of the peripheral zone of the pericarp. The warts of taxa of Livistoninae develop at the mid stages of fruit organogenesis and are referred to as either alive, composed of parenchymatous cells and sclereids (species of Licuala and Pholidocarpus), or dead, consisting of cells with suberized walls and sclereids (Johannesteijsmannia). The nests of sclereids comprising the stone of Johannesteijsmannia spp. remain disunited during pericarp development until late developmental stages when the formation of a continuous sclerenchymatous layer occurs, which differs from other representatives of the 'apocarpous clade' of Coryphoideae with a continuous layer of sclereids persisting during fruit development (as in L. bintulensis). It is shown that the development of the stone within the drupes of the Rhapis type can be different even in closely related taxa. The recognition of the fruits of studied taxa of Livistoninae as drupes of the Rhapis type like the fruit of many other taxa of Trachycarpeae and the 'apocarpous clade' of Coryphoideae suggest this character as a synapomorphy for this tribe and the whole clade.