Ceratophyllum demersum - Submerged Hornwort

Ceratophyllum demersum, also known as Hornwort, is an aquatic plant species with rootless stems. In its natural habitat, some leaves transform into root-like organs that anchor the plant to the soil. This plant helps fight algae in domestic ponds through aggressive competition: it consumes the same nutrients and produces harmful substances that inhibit their growth. It is also an excellent food source for herbivorous fish.

The Hornwort is a submerged aquatic plant belonging to the Ceratophyllaceae family, a species that is widespread worldwide. Its long, feathery-looking stems are surprisingly rigid and can grow over 50cm (20in) in length, with rapid growth. Its dark green leaves, arranged in close whorls along the stem, are divided into thread-like segments and measure 1 to 4cm (1 to 2in) in length. Tiny flowers appear in summer, followed by hard fruits with two spines at the base and a small terminal spine. It should be noted that its elegant, airy branching, contrary to the rough appearance, is brittle and makes transportation somewhat unpredictable. It reproduces through hibernaculum: this refers to a winter bud that forms at the tip of the stem; it falls to the bottom of the water in autumn and develops the following spring.

The Hornwort is a wetland species and prefers slow-moving or stagnant bodies of water. It can be weighted down with a lava stone to secure it in a specific location in the pond, or left to float. It quickly forms dense clumps and provides numerous refuges for fry or timid fish. Its colour varies depending on iron content, light intensity, and temperature. This fast-growing plant should be regularly pruned to limit its growth. When the size of the pond allows, it is preferable to install two to three species of submerged plants to vary the foliage.

Ceratophyllum demersum is recommended for both deep ponds and aquariums to combat algae. It also has oxygenating properties. This plant can lower nitrate levels in the aquarium. Due to the rigidity of its leaves, this species is well-suited for cichlid tanks and is particularly recommended for algae-infested tanks.