The water fern floats on the water's surface along with lesser duckweeds and wolffia. Most of the time, water ferns make new plants by being broken up by waves or water animals. The broken parts can then grow into new whole plants. The single leaf is lobed or branched, and scaled like a moss. The leaf is only 7.6 mm across and reddish-green.
Tiny roots grow from the base of the leaf.
The water fern has a symbiotic relationship with a blue-green algae, 'anabaena azollae'. The algae 'fixes nitrogen' for the fern. That means that the algae takes nitrogen gas from the air or water and changes it to a form that the fern can absorb and use for growth. In return, the fern gives the algae growing inside it a protected place to live. Water ferns form reddish-green mats on the surface of still water.