Mangroves are a group of salt tolerant plant species that occur in the Tropical and subtropical intertidal estuarine regions, sheltered coast lines and creeks and are dominated by partly submerged sclerophyllous plant species that are taxonomically unrelated. Mangroves constitute a
dynamic ecosystem with a complex association of species, both of flora and fauna, of terrestrial and aquatic systems and the vegetation presents an evergreen type with varied life forms. Mangroves stabilize loose soil and detritus, act as a filter for land runoffs, prevent sea erosion and protect the hinterland from tidal surges, cyclonic storms and high velocity winds. Mangroves have four major functions:
Help in soil formation by trapping debris.
Serve as a sieve for rich organic soil washed down through river systems into sea.
Provide appropriate ecosystem and refuge for fish, marine invertebrates, mollusc and birds.
They contribute detritus enhancing the productivity of the ecosystem.
Mangroves have different mechanisms for salinity tolerance. Some species store the salt in older leaves and others secrete the excessive salts through excretory glands. Root system of Mangroves also shows a number of adaptations to suit the salt marsh habitat. Some mangrove genera like Rhizophora have ‘aerial’ or ‘prop’ or ‘stilt roots’ and genera like Avicennia possess ‘pneumatophores’ or ‘breathing roots’. Another important adaptation is Viviparous seedlings (germinating of seeds into seedlings while attached to the parental plant) and dispersal of seedling through water.
In India there are 59 species of mangroves under 41 genera and 20 families. In Tamil Nadu mangrove vegetation is mainly seen in
Pichavaram. Pichavaram covers an area of about 14 sq km of dense mangrove vegetation. Apart from Pichavaram they are seen in Gulf of Mannar and backwater regions of
Ennore. In Tamil Nadu there are 22 species of mangroves under 16 genera and 13 families.
LIST OF MANGROVES SEEN IN TAMIL NADU
||Acanthus ilicifolius L.
||Aegiceras corniculatum (L.) Blanco
||Avicennia alba Blume
||Avicennia officinalis L.
||Bruguiera cylindrica (L.) Blume
||Bruguiera gymnorrhiza (L.) Savigny
(Griff.) Ding Hou
||Excoecaria agallocha L.
||Heritiera littoralis Dryand
||Kandelia candel (L.) Druce
(Nees ex Steud.)Hook.F
||Rhizophora apiculata Blume
Buch. – Ham.
The mangrove on the East Coast are dwindling and species vanishing due to anthropogenic activities. There is over exploitation that has led to degradation and shrinkage of mangroves and vanishing of species as a result. Species like Bruguiera gymnorrhiza and Acanthus ilicifolius collected earlier in Rameswaram have not been recollected in recent years. Vegetation is undergoing severe damage because of firewood collection. Rapid industrialization all along the mainland coast and increase in the extent of saltpans in areas like Tuticorin are the other major reasons for the disappearance of mangroves in the recent past.
Major Gaps on Floral Diversity Research
state of Tamil Nadu has been well explored
for plant diversity for the past three
centuries. However, there are regions that
are under explored. These regions are
floristically rich and harbour several
endemic and threatened species as well as
undescribed species. For example,
exploration of Meghamalai in Theni district
by Dr. K. Ravikumar has resulted in the
discovery of Nothopegia vajravelui (Anacardiaceae),
Syzygium sriganesanii (Myrtaceae), Syzygium
zeylanicum var. magamalayanam (Myrtaceae),
Sonerila parameswaranii (Melastomataceae),
Schefflera maduraiensis (Araliaceae),
Hedyotis shettyi (Rubiaceae) and Anisochilus
henryi (Lamiaceae). Similarly, studies on
Southern Western Ghats have resulted in
several species being rediscovered after the
type collection as well as in the discovery
of many new taxa.
The regions that need to be explored in detail include:
1. Western Ghats of Kanniyakumari and Tirunelveli districts.
2. Offshoots of Western Ghats such as Meghamalai and Azhagar Hills.
3. Hill ranges of Eastern Ghats such as
Kolli, Javadhi and Kalrayan.
4. Specialized habitats such as hill streams and rivers.
Apart from areas that need a detailed exploration, there are several plant groups that need to be studied in detail. Families that possess more number of endemic taxa such as
Balsaminaceae, Lauraceae, Myrtaceae and Melastomataceae require a thorough study. Similarly, Monocot families such as
Arecaceae, Commelinaceae, Cyperaceae, and Orchidaceae also need to be studied in detail. Revision of a number of families and genera is an urgent necessity to comprehend the information that is available from different branches of Botany.Population biology of endemic and threatened species should be the focus for all taxonomists and ecologist as there is a paucity of data in this area. Preparation of precise distribution maps for such taxa using modern tools such as GIS is much needed. There is a renewed interest in traditional systems of medicine and as a consequence in medicinal plant trade. Hence, floristic research should concentrate on a number of aspects of medicinal plants, not only to provide information, but also to monitor the bulk collection of medicinal plants.
Database on Floral Diversity of Tamil Nadu
This database on Flowering Plants of Tamil Nadu has been compiled based on existing published literature. They include Floras, Journals and Revisions. Nomenclature and distribution data has been updated. A number of unpublished dissertations and theses were also referred for the data on distribution. Synonyms are not included in this database.
An overview of the statistical details of the flora of Tamil Nadu show that there are 5547 taxa distributed in 231 families with the total number of Genera 1668, Species 5239, Subspecies 72 and Varieties 548 respectively. The arrangement of families in this database is based on Bentham and Hooker’s system of classification, which is widely followed in India. The analysis provided the total number of plants in
Polypetalae, Gamopetalae and Monochlamydeae to be 1944, 1720 and 642 respectively. Distribution of plants in different plant groups namely Dicots and Monocots had a total of 4306 and 1241 taxa respectively. The study included a total of 270 as strict endemics. The top ten families of Tamil Nadu according to the analysis of this database show that Leguminosae
s.l., Poaceae and Compositae are the most dominating families followed by
Rubiaceae, Orchidaceae, Euphorbiaceae,
Cyperaceae, Acanthaceae, Labiatae and
Myrtaceae. New species, varieties and new records that are described from the state of Tamil Nadu within the past 10 – 15 years are also included from the available literature, which are about 48 in number.