Ecoanatomical characterisation and development of anatomical key of selected mangrove species of west coast of India

Abstract

The present investigation focused on the ecoanatomical characterisation of the wood of 17 selected true mangroves collected from 10 locations in the Western Coast of India. A total of 221 characters listed in the IAWA (International Association of Wood Anatomists) list of card key features were studied for each species as there is a felt need for creating databases of mangrove wood anatomy which allows to quantify the relative amount of intra- and interspecific variation, as well as variation within and between the mangrove genera. Mangrove wood from West Coast of India is characterised by diffuse-porosity, scalariform to opposite vessel wall pitting, scalariform perforations with few bars or large number of bars. Most mangrove family members were found to have simple perforations, septate or non septate fibres with distinctly to minutely bordered pits, bordered, half bordered to simple pits, paratracheal parenchyma, apotracheal and banded parenchyma. Heterocellular to homocellular rays with mostly procumbant cells with one or several marginal row of square/upright cells was also observed in these mangrove genera. Short numerous vessels with small dimension and vessel grouping were also common. The most advanced characters like vestured pit, helical thickening, crystals and vessel occlusions were present in majority of the samples. A perforated card key based on the IAWA list of microscopic card features for mangrove identification was also prepared. The development of an IAWA based anatomical key will be helpful for the identification of mangrove species based on wood anatomy. The ecoanatomical characters such as vessel diameter, vessel frequency, vessel grouping, type of vessel plate, lateral wall pitting, type of pits of true mangrove species were studied and compared with data from their nearest upland relative. The ecoanatomical features of wood of mangrove species are correlated with xeromorphic nature of their upland relatives. Because of the highly variable and stressful environmental condition, the mangroves developed certain strategies and adaptations during their evolution. These special morphological and physiological adaptations made it for the mangrove species to survive in these conditions in contrast to their upland relatives. A safe hydraulic architecture is only one of the alternative ways for a plant to be able to survive in water stress situations. The modification of xylem hydrological structure of mangrove wood helps to balance safety versus efficiency of water transport system. These modifications of wood structure due to ecological conditions are the driving force to evolution of wood anatomy. Thus the evolution of mangrove genera has been shown to be likely driven by environmental condition and not by phylogeny. The general pattern of wood anatomy of mangrove genera of different families indicates convergent evolution. These trends of wood anatomy in mangrove species provide new examples of phenotypic plasticity in angiosperms. To ensure safety, certain primitive structures such as bordered pits, scalariform vessel plate, scalariform, transitional, opposite lateral wall pitting and vessel bars still persist in the true mangrove genera of the present investigation. Thus the development of wood anatomical characters in mangrove genera were an example of heterobatmy. The presence of mostly primitive wood character states suggest an unbroken occupancy of stressful habitat by its ancestral genera. Mangrove occurs in different families in which the gamut of wood specialization ranges from advanced to highly advanced features. Rhizophoraceae members were found to be the most primitive ones with less specialization whereas the other mangrove species were found to have highly advanced wood anatomical characters.