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Ceratophyllum demersum
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Ceratophyllum demersum

Common Names: Hornwort
Common Hornwort
Rigid Hornwort
Coontail
Distribution: A cosmopolitan species. Native to North America, found as far north as Alaska and as far south as Texas. Introduced but considered naturalised in Europe - one current field guide to UK flora lists the species as 'Native or commonly naturalised throughout the United Kingdom'. European range extends from Norway in the north to Serbia and Montenegro in the south: UK in the west to Russian Federation in the east. Also found in China and Japan, and as an introduced pest in Australia and New Zealand.
Description: Brittle, fine leaved plant, leaves arranged in whorls around the stem. Leaves are somewhat reminiscent of pine needles in basic shape, but unlike pine needles, the leaves of Hornwort are branched. Plant possesses no roots, but instead absorbs nutrients throughout its entire tissue mass. Stems branch as the plant grows, resulting in tangled masses of growth in the wild. The natural growth habit of the plant is to form masses floating in the water, not attached to the substrate, with no part of the plant emerging from the water.
Potential Height: 150cm   (59.1")
Growth Rate: Fast
Care: One of the easiest of all plants to grow in an aquarium setting. Even under modest lighting, it grows quickly, and requires ruthless pruning to keep it in check - growth rates of as much as three inches per day are observed when the plant is placed in a well lit tropical aquarium. The extremely brittle nature of the plant makes it troublesome as a decorative plant (as does the inability to attach it to the substrate) but the plant was at one time popular with photographic illustrators of fishes - the Innes book contains numerous illustrations depicting this plant as a background plant. Tremendously useful in a fry rearing aquarium, where the plant provides both cover for developing baby fishes, and a solution to nitrogen cycle management in environments where powerful filter currents cannot be used. A particularly useful plant for use in maternity aquaria for livebearers, where in combination with Java Moss, it will provide a refuge for the newly delivered fry, and also useful in breeding aquaria for many common egg-laying fish species such as Danios, small Barbs, Tetras etc. Any aquarium containing fishes will provide the plant with an ample source of nutrients to be absorbed. Will grow in both coldwater and tropical aquaria. A related plant, Ceratophyllum submersum, is described in Flora Europaea as being capable of growing in brackish estuaries, but this species is strictly freshwater. In outdoor ponds, can survive severe winter weather so long as the body of water in which it is growing does not freeze solid - in such circumstances, the plant prepares for winter by becoming denser than the surrounding water, sinking away from the water surface, and thus avoiding becoming trapped in surface ice.
Difficulty: Easy
Temperature:
4°C - 35°C
39°F - 95°F
pH:
5 - 9
Hardness
0.5 dH - 25 dH
Lighting: A plant that will grow under a vast range of lighting conditions. Appears to fare best when lighting levels are moderate to high - too low a light level causes the plant to die off (though the plant has to be kept in very gloomy conditions for this to happen), while lighting that is too intense encourages rank, stringy growth.
Propagation: Though the plant is a flowering plant, and in the wild will reproduce sexually in suitable conditions, aquarium propagation usually takes the simple form of breaking off branching parts of the parent plant and allowing these to grow independently. It is possible to produce truly prodigious quantities of this plant by this means, and indeed, in some localities to which the plant has been introduced as a non-native, it constitutes an invasive pest because even small broken pieces of stem are capable of becoming a complete new plant.
Comments: As a UK and European natrualised plant, this species is not problematic for UK and European aquarists from the standpoint of invasive species. While it is an American native, American aquarists should check their appropriate regulations with respect to the status of this plant in their locality, as overabundant growth of this plant in the wrong watercourses constitutes an ecological management problem in some localities. Unlikely to be available to Australian and New Zealand aquarists, as the plant is classified as an unwanted alien in those countries, and in the case of New Zealand, the plant is listed on the National Pest Plant Accord of the Royal New Zealand Institute of Horticulture.
Image Credit: Calilasseia
Submitted By: Calilasseia
Contributors: Calilasseia
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