Aquatic PlantsBeginner🌑 Low light

Hornwort

Ceratophyllum demersum · also called Coontail, Rigid hornwort, Ceratophyllum

🐾 Pet-safe

Generally non-toxic to cats and dogs.

An extremely hardy, rootless floating or anchored plant with whorls of stiff, forked needle-like leaves. A prolific nutrient absorber and oxygenator that thrives in almost any condition.

Educational only. KinStation content is reviewed by licensed veterinarians but cannot replace an in-person exam. Always consult a licensed veterinarian or board-certified specialist for diagnosis, treatment, or any decision affecting your pet's health.

Quick facts

Category	Aquatic Plants
Family	Ceratophyllaceae
Native origin	Cosmopolitan (native across North America, Eurasia, and other continents)
Care difficulty	Beginner
Light	Low light
Pet toxicity	Pet-safe

Light

Tolerates very low to high light. Grows in low light without issue; brighter light simply speeds growth. One of the few plants that does well even in dim, low-tech setups.

Water

Very wide tolerance: temperature 15-30 C (59-86 F), pH 6.0-7.5, soft to hard water (GH 5-15). Survives unheated tanks and ponds. Absorbs nutrients directly from the water column, so it thrives on fish waste with little or no added fertilizer.

Soil & potting

Rootless — it has no true roots and is not planted in substrate (and is not an epiphyte). Let it float, or weigh/anchor a bundle near the bottom; any 'roots' that form are just modified leaves used to grip. It feeds entirely through its stems and leaves from the water column, so substrate type is irrelevant.

Environment — humidity, temperature, placement

No CO2 needed. Use as a floating plant to provide shade and fry cover, or anchor it as a background bush. Prefers gentle flow (strong flow scatters it). Strictly submersed/floating aquatic; it has no true emersed form. Note it commonly sheds needles when first introduced or when conditions shift.

Propagation

Propagate simply by cutting or breaking off any portion of stem — each fragment continues growing as a new plant. Side shoots form continuously. Growth can be explosively fast under good nutrients and light.

Toxicity detail

Non-toxic and safe with fish and shrimp; widely used in shrimp and fry tanks. However, Ceratophyllum demersum is a serious invasive where introduced — it is New Zealand's worst invasive submerged macrophyte, where its sale and distribution are prohibited (classed as an unwanted organism) — and it is listed/regulated in various other jurisdictions. Never release it into the wild and dispose of trimmings in the trash.

Growth stages

How this plant changes through its life — each stage often has its own care, diet and space needs.

Photo coming soon

Spore / recruit

Aquatic plants and macroalgae establish from spores, seeds, or drifting fragments that settle and attach to substrate or rock. Many freshwater aquarium plants and marine macroalgae also spread readily from a detached piece that takes root or holdfast.

Photo coming soon

Young growth

Young growth puts out its first blades, fronds, or leaves and anchors with roots or a holdfast. Submersed plants may look different from their emersed form, and growth speeds up as the plant adapts to the water's light and nutrients.

Mature

A mature aquatic plant or macroalga reaches its full size and characteristic shape, forming the dense growth, runners, or fronds typical of the species. Established plants spread to fill space and can be divided or trimmed to propagate.

Sources

Ceratophyllum demersum - Wikipedia (encyclopedia)
Ceratophyllum demersum - Aquasabi Aquascaping Wiki (care guide)