Hornwort (Ceratophyllum demersum), also known as Coontail, has sturdy, layered hair-like foliage that helps oxygenate and clarify the water as well as keep algae growth to a minimum. It is found free-floating worldwide, in moving and still waters, or loosely anchored in muddy bottoms.
The tips will shorten and thicken in fall, before falling off and settling on the pond floor to spend the winter as buds. In spring, these buds grow to repopulate the pond.
Hornwort leaves are dark green and grow from a 1/2 to 1-1/2 inches long on stems that can reach 24 inches in length. They may be potted or just left to float in the pond.