Pistia stratiotes or Water Lettuce is an aquatic perennial with wide floating rosettes of ribbed, wedge-shaped leaves that resemble lettuce heads.
The bases of the leaves are spongy which keeps them buoyant.
The roots extract nutrients directly from the water.
Best grown in containers either as a feature (en-masse) or as an accent to other aquatic plants.
Unless controlled it can be quite invasive - so care should be taken.