Mangrove Ecosystem: An Overview Mangroves: Definition and Types ‘Mangrove’ has been variously defined in literature. The Oxford dictionary mentioned the words ‘mangrove’ since 1613, indicating tropical trees or shrubs found in coastal swamps with tangled roots that grow above the ground. Later, the term ‘mangrove’ was referred to the individual plant or tidal forest or both, as ‘Mangrove plants’ and ‘Mangrove ecosystem’ (MacNae 1968). Chapman (1984) used the term ‘mangrove’ for inter tidal plants, and considered plant communities of inter tidal forest as mangrove ecosystem called ‘mangal’. The term ‘mangal’ was also commonly used in French and in Portuguese to refer to both forest communities and to individual plants. Several workers have opined that plants growing in between the highest and the lowest tidal limits may be considered ‘mangrove’ (Aubreville, 1964; MacNae, 1968; Blasco, 1977; Tomlinson, 1986; Naskar & Guha Bakshi, 1987). The tidal limits of various habitats, however, can vary. Mangrove plants comprise a heterogeneous group of independently derived lineages that are defined ecologically by their occurrence in tidal zones along shorelines and in estuaries and physiologically by their ability to withstand high salt concentrations and low soil aeration. Based on their abundance, distribution, and habitat specificity, Tomlinson (1986) distinguished major and minor mangrove elements as well as mangrove associates. He recommended that mangrove species were basically of two types, viz., (1) Major element of mangals or true mangroves – with complete fidelity to the mangrove environment, and (2) Minor element of mangals – not conspicuous in mangrove habitats, rather might prefer the peripheral habitats of mangrove regions. The term ‘Mangrove associate’ was coined for the flora representing nonarborescent, herbaceous, sub-woody and climber species, found growing mostly in regions bordering the tidal periphery of mangrove habitats. Tomlinson (1986) used fairly rigid criteria to distinguish true mangroves from mangrove associates. In his criteria, true mangroves possess all or most of the following features: (i) occurring only in mangrove environment and not extending into terrestrial communities; (ii) morphological specialization (aerial roots, vivipary); (iii) physiological mechanism for salt exclusion and/or salt excretion; (iv) taxonomic isolation from terrestrial relatives.