Micromorphology and Adaptation of leaf epidermal traits in Rhizophoraceae to Coastal Wetland Ecosystem

Abstract

The leaf epidermal/cuticular micromorphological feature was studied in four genera vis-a-vis Rhizophora, Kandelia, Ceriops and Bruguiera of family Rhizophoraceae. While Rhizophora has the means to exude excess salt through their stomatal modification (cork-wart-like structure), Kandelia shows rupture in the epithelium perhaps for the same reason. No cork-wart-like structure was found in Kandelia, Ceriops and Bruguiera species. The epidermal cell size, stomatal length and breadth, stomatal index and differentiation in the costal and intercostal cell wall pattern are the identifiable traits in all the species studied. Rhizophora apiculata and Bruguiera caryophylloides shows increase/ decrease in the epidermal cell size and Stomatal indices with the varying coastal ecology.

During salinity related stress the cork-wart-like structure in Rhizophora apiculata on the lower epidermis becomes rudimentary and non-functional while it is well developed and of larger size in normal ecological conditions. Bruguiera cylindrica differs with all the species in having undulate cell wall pattern in the costal area studded with the stomata and shows closer affinity with B. gymnorrhiza (costal cells distinct but with sinuate anticlinal cell wall) and not with its Syn. B. caryophylloides in this respect. The stomatal index (SI) in Rhizophora apiculata shows similarity with that of Bruguiera parviflora and B. gymnorrhiza . However, R apiculata growing in stressed environment shows similar SI as in Bruguiera sexangula and other species of Rhizophora, Ceriops and Kandelia . It is understood that perhaps Rhizophora apiculata and C. decandra (Syn. C. roxburghiana ) and B. cylindrica (Syn . B. caryophylloides ) have SI as a non-consistent feature that tends to vary with the changing environment. Mangrove species showing similarity in the epidermal traits and their adaptive features may thrive together in a common coastal environment. Leaf epidermal traits of Rhizophoraceae would help in the identification of fossil cuticles at the specific level and their non-consistent features adapting to the changing coastal environment would provide potential proxy data for interpreting palaeoecology.