Synopsis Biodiversity of aquatic and semi aquatic plants constitutes an integral component of any aquatic ecosystem. They serve as a source of food and shelter for the aquatic fauna, thus forming the base of aquatic wildlife conservation practices. They are economically useful in providing medicinal and aesthetic values and may serve as a good source of fertilizer. An account of diversity of aquatic plants is necessary for preventing and maintaining excessive erosion, turbidity of water, and source of oxygen for respiration and provides protection against hot and cold weather to aquatic fauna. This book has been written with a hope that it will work as a reference to botanists, agriculturists, forester, ecologists and ethnobotanists. The book includes introduction, geographical position, vegetational composition and key to the families in addition to the description of plants. Number of species described are 751. This includes phanerogams and the vascular cryptogams with illustrations and photographs to facilitate their easy identification. The families of angiosperms have been arranged according to Bentham and Hookers system (1872) whereas families of vascular cryptogams to that of Smiths system of classification (2006). Each species has its correct name, basionym (if any), important synonyms, concise description, ecological association, ethnobotanical information and the phonological data. The work is of fundamental importance for the persons interested in further exclusive studies on taxonomy, ecology, embryology of the plants including the ethnobotany, forestry and soil conservation.