Which of the following plant is used for the purification of water.

Eichhornia is scientific name of water hyacinth. Water hyacinth pond is used in effluent treatment plants. Other such organisms are Azolla, Lemna, Salvinia, etc. They have potential of environmental clean up, because they can tolerate, uptake and even accumulate heavy metals and other toxicants in their cells. So, the correct answer is 'Eichhornia'