Ceratophyllum spp.

hornwort

Ceratophyllaceae Worldwide in fresh water

Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterHigh

HardinessZones 3–11

Overview

Ceratophyllum spp. 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 spp. 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

A rootless submerged plant with long, branching stems bearing whorls of stiff, repeatedly forked dark green leaves edged with tiny teeth, giving a bristly, brush-like feel. Plants drift free or rest loosely on the bottom. There are no roots, and broken stem pieces grow into new plants.

Appearance

Size & Dimensions

Height1' - 10'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~8 weeks

Summer

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, inconspicuous

Foliage Description

dark green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

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

Soil Requirements

pH Range6.0 - 8.5(Alkaline)

357912

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

Establishes within one season

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.