Ceratophyllum demersum
coontail
Cosmopolitan in temperate and tropical fresh water
Container Friendly
Native to North America
Overview
Ceratophyllum demersum, coontail or rigid hornwort, is a submerged, free-floating aquatic perennial in the family Ceratophyllaceae that grows entirely underwater without true roots. Its slender stems, often 12-79 inches (30-200 cm) long, carry dense whorls of stiff, dark green leaves, each forked once or twice into narrow, brittle, finely toothed segments that crowd toward the stem tips like a raccoon tail. The plant anchors loosely by modified pale shoots that bury in sediment, but it drifts freely if dislodged. Tiny petal-less flowers form in the leaf axils; the plant is monoecious, and pollination happens underwater, with the male pollen released to drift to the female flowers. It spreads mainly by stem fragments and by dense, leafy winter buds (turions) that sink and overwinter. Found in still and slow-moving fresh water on several continents, it tolerates low light and a wide range of water chemistry, and it releases compounds that can hold back algae and competing plants. Dense growth can crowd ponds and slow waterways, which is its main drawback in managed water.
Native Range
Ceratophyllum demersum has a near-cosmopolitan distribution, occurring across the Americas, Europe, Asia, Africa, and Australia in lakes, ponds, ditches, and slow rivers. It grows submerged in still and gently flowing fresh water.Suggested Uses
Grown as a submerged oxygenating plant in ponds, wildlife pools, and aquaria, where it shelters fish fry and aquatic invertebrates and competes with algae. It is added by dropping or loosely weighting bunches of stems into the water.How to Identify
Appearance
Size & Dimensions
Height1' - 6'7"
Width/Spread1' - 3'
Reaches mature size in approximately 1 years
Bloom Information
Flowering takes place underwater in summer, with minute petal-less flowers in the leaf axils. The plant is monoecious, and pollen is released into the water to reach the female flowers, a form of fully underwater pollination. Small nut-like fruits with marginal spines may follow, though spread is mostly by stem fragments and winter buds.
Detailed Descriptions
Flower Description
greenish, inconspicuousFoliage Description
dark greenGrowing Conditions
Sun Requirements
Requires 2-10 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Ceratophyllum demersum grows submerged in still or slow fresh water in full sun to part shade and needs no soil or planting, drifting freely or loosely held in sediment. It tolerates a wide pH and hardness range, cool to warm water, and low light, which makes it widely grown in aquaria and ponds as an oxygenating plant. It takes up nutrients directly from the water and can curb algae by competing for them. In warm, nutrient-rich water it grows quickly and may need thinning to keep ponds open. It overwinters as turions that sink and resprout in spring, and it is increased simply by dividing the stems. No feeding is required.Pruning
Excess growth is thinned by lifting and removing handfuls of stems through the growing season to keep open water. Broken fragments readily grow into new plants, so removed material is taken well away from natural water. No other maintenance is needed.Container Growing
✓ Suitable for container growing
Minimum container size: 5 gallons