Fruit Development and Pericarp Structure in Nypa fruticans Wurmb (Arecaceae): A Comparison with Other Palms

Abstract

Nypa fruticans is a mangrove palm with current natural coastal distribution in the Old World tropics and hydrochorous fruit dispersal. Nypa comprises its own monotypic subfamily in Arecaceae, with high or moderate support of its sister position to other palms excluding Calamoideae or even sister to all other palms including Calamoideae. Apocarpous Nypa fruits develop from a spherical female partial inflorescence into large, tightly packed capitate infructescences. Important anatomical features of Nypa fruits (drupes of the Rhapis type) are the single-layered exocarp and endocarp, while the mesocarp is thick and multilayered; its differentiation into a hypodermis and three topographic layers is initiated in the gynoecium shortly after pollination. The outer mesocarp layer transforms into complex aerenchyma at late developmental stages, the massive stone constitutes the second mesocarp layer, and the innermost multilayered parenchymatous mesocarp layer is highly compressed and partly obliterated in mature fruit as a result of seed growth. The mode of pericarp development in Nypa is nearly identical in most aspects to those described for paracarpous fruits of Eugeissona (Calamoideae) and syncarpous fruits of all genera of Borasseae (Coryphoideae). Carpological features support the close relationship of Nypoideae, Calamoideae (Eugeissona), and Coryphoideae (Borasseae). Nypa fruits show little similarity to those of Coryphoideae (excepting Borasseae), Ceroxyloideae, and Arecoideae.