English: Pistia , Water Lettuce
Malayalam: കുഴിതാമര
Hindi: पिस्टिया स्ट्रेटिआइटीज
Tamil: ஆகாயத்தாமரை

Local Name: Kodi-thamarai, Agasa-thamarai, Kuzhi-thamarai

Pistia is a genus of aquatic plant in the arum family, Araceae. The single species it comprises, Pistia stratiotes, is often called water cabbage, water lettuce, Nile cabbage, or shellflower. 

Water Lettuce is an aquatic plant found floating on lakes, lazy streams and on stagnant water which is rich in lime.

Wikipedia  Ayurveda