Azolla caroliniana

Azolla caroliniana is a small floating fern housing blue-green algae in its leaves. This algae is capable of absorbing nitrogen from the air, which can then be used by the plant. Water resistant. A. caroliniana now occurs all over the tropics, where it has become a menace because it covers lakes and deprives the original aquatic plants of light. Used as nitrogen fertiliser in rice paddies, and some varieties used as animal feed. Several related varieties on the market, with similar appearance. A decorative plant for open aquariums.