Palm snorkelling: Leaf bases as aeration structures in the mangrove palm (Nypa fruticans)

Abstract

Mangrove species have evolved specialized structures, such as pneumatophores, to supply oxygen to the roots, but, in Nypa fruticans, the only mangrove palm, no such structure has been reported. This study aimed to determine the adaptations of N.fruticans to the mangal habitat with special reference to the air-supplying structure. Following senescence, the rachis is abscised at the zone of junction with the leaf base. Simultaneously, lenticels develop so that, when abscission is completed, a network of mature lenticels covers the leaf base. Expansigenous aerenchyma with increasing porosity towards the stem junction occurs in the leaf base. The first two root branching orders present a subero-lignified rhizodermis and exodermis, and the cortex consists of schizo-lysigenous aerenchyma with wide lacuna, limiting radial oxygen loss and facilitating longitudinal oxygen transport to living tissues. Lifespan estimation suggests that leaf bases can live for up to 4years following abscission, ensuring the persistence of aeration structures. This study provides structural evidence indicating that N.fruticans has evolved a unique type of air-supplying structure in the mangal habitat. © 2013 The Linnean Society of London.