Water hyacinth:

water hyacinth, any aquatic plant of the genus Eichhornia of the pickerelweed family (Pontederiaceae), consisting of about five species, native primarily to tropical America. Some species float in shallow water; others are rooted in muddy stream banks and lakeshores. Water hyacinth is a free-floating perennial aquatic plant (or hydrophyte) native to tropical and subtropical South America. With broad, thick, glossy, ovate leaves, water hyacinth may rise above the surface of the water as much as 1 m (3 ft) in height. Water hyacinth is a perennial, free-floating aquatic plant native to tropical regions of South America, and now present on all continents except Antarctica. Water hyacinth forms dense colonies that block sunlight and crowd out native species and is regarded as the most troublesome aquatic plant. Water hyacinth is not an indigenous species but was introduced to India during the British colonial rule as an ornamental aquatic plant from South America.