water-shield

from The Century Dictionary.

• noun A plant of either of the genera Cabomba and Brasenia, which form the suborder Cabombeæ, of the Nympheaceæ: so called as consisting of aquatics with peltate leaves.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun aquatic plant with floating oval leaves and purple flowers; in lakes and slow-moving streams; suitable for aquariums
• noun common aquatic plant of eastern North America having floating and submerged leaves and white yellow-spotted flowers