Azolla

Azolla (Azolla caroliniana). Very small floating plant, often called fairy moss, with tiny scale-shaped leaves. It provides a thick lacy velvet carpet of floating bluish-green or, in the autumn a brilliant crimson congested foliage that is very beautiful. An interesting characteristic of Azolla is that it has a mutual living relationship with alga that "fixes" or prepares nitrogen from the atmosphere for the tiny plant as food. Per Portion.