Bangladesh is situated in the “oriental region”, between the Indo-Himalayas and Indo-Chinese sub-regions. The country covers an area of 147,570 km, of which about 80 % comprises deltaic plains—one of the largest in the world, formed at the confluence of the Ganges, the Brahmaputra (Jamuna), and the Meghna rivers. The remaining 20% of the land area comprises of the undulating, forested Hill Tracts. Distinct physiographic characteristics, variations in hydrological and climate conditions, and differences in the soil properties in Bangladesh contribute in developing diverse forms of ecosystems enriched with great diversity of flora and fauna.
Bangladesh possesses rich species diversity particularly for angiosperm and avifauna. Out of the total 3,611 species of angiosperm, about 2,623 species under 158 families belong to dicotyledons and about 988 species under 41 families to monocotyledons, while the number of reported bird species is 650 for the country. It comprises of approximately 150 species of birds fully or partially dependent on wetland, more than 80 species in 37 families of mammals, reptiles and amphibians, 251 species of freshwater fi sh and many more estuarine fish species.