Mangroves can be classified into three broad categories. True mangroves are mainly restricted to intertidal areas between the high water levels of neap and spring tides. Plant species from true mangroves belong to at least 20 different families. About 80 species of true mangrove trees/shrubs are recognized, of which 50-60 species make a significant contribution to the structure of mangrove forests. Minor species of mangroves are distinguished by their inability to form conspicuous elements of the vegetation and they rarely form pure communities. The mangal associates are salinity tolerant plant species, which are not found exclusively in the proximity of mangroves and may occur only in transitional vegetation, landwards and seawards. However, they do interact with true mangroves

Metabolites, some with novel chemical structures, and belonging to a diversity of "chemical classes", have been characterized from mangroves and mangal associates.

Two basic factors justify the study of the chemical constituents of mangrove plants.

Firstly, mangroves are one of the easiest tropical forest types to generate. They have the ability to grow where no other vascular plants can. The mangroves exist under stressful conditions such as violent environments, high concentration of moisture, high and low tides of water, and abundant living micro-organisms and insects. They thrive in a very peculiar environment and serve as a bridging ecosystem between freshwater and marine systems. These have imposed several modifications in these plants. They possess modifications to establish water and salt economy. There are modifications or alterations in other physiological processes such as carbohydrate metabolism or polyphenol synthesis and due to these reasons, they may have chemical compounds, which protect them from these destructive elements. (Mangroves and Salt Marshes, 1998).

The second reason is that numerous mangrove plants are been used in folklore medicine, and recently, extracts from mangroves and mangrove-dependent species have proven activity against human, animal and plant pathogens but only limited investigations have been carried out to identify the metabolites responsible for their bioactivities

Marine organisms and plants produce novel metabolites unique to the environment. Mangroves and mangal associates living in yet another different environment to that of marine and terrestrial plants, can produce metabolites, which may in turn, are unique to these plants and are of interest to the "curious" chemist. Although the chemistry of the natural products of mangrove plants is little known, there have been some examples in recent years to support the need to study the chemistry of the mangroves. The chemistry of mangrove plants tends to establish that they may be a source of novel compounds along with providing a new source for many already known biologically active compounds. They may have great potential as a source of novel pesticides and agrochemical compounds. They are also a rich source of toxic compounds. Toxin in plants often has the role of feeding repellents. A remarkable number of insecticidal plants seem to have been recognized first as fish poisons. Knowledge of the toxins in higher plants has led to a variety of useful drugs. A knowledge of the chemical constituents of these plants is desirable, not only for the discovery of new therapeutic agents, but because such information may be of further value to those interested in "deciphering" the actual value of folklore remedies.

A review article to be published shortly (Wetlands Ecology and Management, 2002) presents the traditional and medicinal uses, and examines past and present investigations on the biological activities of extracts, and chemicals identified from mangroves and mangal associates. Metabolites identified from mangrove plants are classified according to "chemical classes", and some of their structures are illustrated.

The article also presents some of the functions of the chemicals present and attempt to emphasize and create an awareness of the great of potential mangroves and mangal associates possess as a source of novel pesticides, agrochemicals, compounds of medicinal value, and a new source of many already known biologically active compounds.

The world of plants, and indeed all-natural sources, represents a virtually untapped reservoir of novel drugs awaiting imaginative and progressive organizations. Further more, infectious diseases are potentially the largest threat to human security. Coupled with continuing threat to biodiversity through the destruction of terrestrial and marine ecosystems and proven record of natural products in drug discovery, there is a compelling argument for expanding the exploration of nature as source of novel active agents.