Hardiness: Very Easy
Light Needs: Low
Plant Structure: Floating
Size: Individual stem width: 3-5cm (1-2in)
Growth Rate: Very Fast
Can Be Grown Emersed: No
Ceratophyllum demersum is a cosmopolitan, ubiquitous, obligate aquatic plant. In its natural habitat, it is typically found floating in stagnant and slow moving water. It is commonly referred to either as Coontail because its tight whirls resemble a racoon's tail, or as Hornwort. The Latin and common names of hornwort come from the Greek keras meaning horn, phyllon meaning leaf, and wort (the Anglo-Saxon word for plant). This species has been in the aquarium trade for many years and is commonly available. It is also widely available as a plant for ponds.
Ceratophyllum demersum is an easy plant to grow in an aquarium. It is a true rootless aquatic that floats just under the surface of the water. It will develop rhizoids if anchored in the substrate. It grows quickly in medium-hard to hard water with temperatures of up to 86F. It is undemanding as far as light levels. It does not require CO2 supplementation although it will increase its already rapid growth. Being a fast grower, C. demersum can take up nutrients quickly. This makes it a good competitor with algae. Additionally, this plant has been known to use allelochemicals to combat algae.
This plant grows quickly and will require constant pruning to keep it in check, just cut off excess growth with a pair of scissors.
Ceratophyllum demersum can be used as part of the aquarium background. Several stems together will create a nice grouping. However, it must be anchored regularly to prevent it from floating up to the surface. In practice, hornwort is better used as a nutrient sponge rather than as a potential plant for creating a serious aquascape.