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Ceratophyllum spp.
hornwort
Overview
Ceratophyllum is a genus of submerged aquatic plants, the hornworts or coontails, in the family Ceratophyllaceae, found in still and slow-moving fresh water worldwide. Plants are rootless and free-floating, drifting below the surface or loosely held in sediment by pale modified leaves. Slender stems reach 1 to 10 feet (30 to 300 cm) long and carry whorls of stiff, forked, dark green leaves with tiny teeth along the edges, giving the foliage a bristly, raccoon-tail look behind the common name coontail for C. demersum. The plant has no true roots and absorbs nutrients across its whole surface. Tiny flowers form in the leaf axils and are pollinated underwater, a rare trait among flowering plants, followed by small hard nutlets bearing spines. Hornworts grow rapidly, multiplying mainly by stem fragments, and overwinter as dense buds called turions that sink and resprout in spring. The genus tolerates a wide range of water conditions and shades out competing algae, though it can become weedy in nutrient-rich water and is regulated in some regions outside its native range.
Native Range
Ceratophyllum has a near-worldwide distribution in fresh water. C. demersum is found on every continent except Antarctica, while C. echinatum and other species have more limited ranges in the Americas and elsewhere.Suggested Uses
Used as an oxygenating and water-clarifying plant in ponds, water gardens, and freshwater aquariums, where it shelters fish fry and aquatic invertebrates. Its fast nutrient uptake competes with algae. It is also used in aquaculture and as cover for spawning fish.How to Identify
Appearance
Size & Dimensions
Height1' - 10'
Colors
Bloom Information
Flowering is inconspicuous and happens underwater, mainly in summer. Minute male and female flowers form separately in the leaf axils, and pollen is released into the water to drift to female flowers. Small spiny nutlets follow. Most spread, though, is by fragmentation rather than seed.
Detailed Descriptions
Flower Description
greenish, inconspicuousFoliage Description
dark greenGrowing Conditions
Sun Requirements
Requires 4-10 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
Hornwort grows fully submerged in still or slow fresh water from full sun to part shade and needs no planting medium, as it has no roots. It is added to ponds and aquariums by dropping stems into the water, where they float or are loosely weighted down. It tolerates a broad pH range of about 6.0 to 8.5 and a wide span of temperatures, slowing in cold water and persisting as turions over winter. Rapid growth takes up excess nutrients and limits algae, so periodic thinning keeps it from filling the water column. In nutrient-rich ponds it can overgrow and need regular removal.Pruning
Thin the floating mass by pulling out or cutting back excess stems whenever it crowds the water. Removed fragments root readily and can spread to natural waterways, so they are bagged and binned rather than composted near water. No seasonal pruning schedule applies.Container Growing
Suitable for container growing