Christmas Moss (Vesicularia montagne) is a species of moss that thrives in freshwater. It can survive in a wide variety of lighting conditions and is a good option for low-light aquariums.
Christmas Moss is extremely versatile; you may plant parts of it in your aquarium substrate to create a "carpet" effect, or anchor it to rocks or driftwood using string or an aquarium-safe glue.
This plant is also able to provide hiding spots (and act as a shelter) for baby shrimp, fry, or small aquatic species.
(Image courtesy of "Wikipedia").