ID ME - Mystry Floating Plant

The plant floats at the water surface. It has roots that can get very long that flow in the water. The leaves are rich color of green and gets hues of purple. It has air filled sacs along it's sections. The leaves resemble the look and feel of a St Augustine grass blade but a lot larger and aquatic. The leave size is .5" wide by 2" tall. I was given a piece of the plant from friend. She cannot remember it's name or who she got it from. I've searched the internet far and wide and cannot find anything. Please help me.