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Ceratophyllum demersum "Mexiko" ("Rotstängelig")

Ceratophyllum demersum "Mexiko"

An elite Mexican variant of Hornwort featuring a striking, highly rigid crimson-red central stem under intense light. Completely rootless, it absorbs massive nutrients from the water column to thrive.

Taxonomy
Class:Magnoliopsida
Order:Ceratophyllales
Family:Ceratophyllaceae
Genus:Ceratophyllum
Species:Ceratophyllum demersum "Mexiko"*
* Rotstängelig

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Check out Ceratophyllum demersum "Mexiko" ("Rotstängelig") on Atlarium

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Water Temperature

15 - 28 °C

pH Value

6 - 8.5

Water type

Freshwater

Light

Medium

CO2

Low

Expected height

80 cm

Expected width

15 cm

GH

4 - 20 dGH

KH

5 - 21 dKH

Species description

Geographical Origin and Habitat: Endemic primarily to the sun-drenched, nutrient-rich lakes, warm sluggish rivers, and flooded marshes of Mexico and Central America. This specific variant of Ceratophyllum demersum (internationally traded as the "Mexiko" or "Red-Stemmed" Hornwort) is an elite, highly specialized aquatic survivor. It shares the same floating, amphibious lifestyle as standard Hornwort, thriving entirely submerged, but it has evolved under the intense, high-UV solar radiation of the Mexican climate, developing extreme pigmentation to protect its tissues.
Taxonomy & Genetics: Scientifically, it is classified simply as a geographic variant of the cosmopolitan Ceratophyllum demersum species. However, in the high-end aquascaping hobby, the "Mexiko" variant is taxonomically highly prized for a specific, profound genetic mutation: its stems. While the standard cosmopolitan Hornwort possesses zero ability to produce red pigmentation, this specific Mexican genetic line forces the production of intense anthocyanin (red/purple) pigments exclusively concentrated within its thick central stem, earning its German trade name "Rotstängelig" (Red-Stemmed).
Physical Structure: The architectural structure of the "Mexiko" variant is identical in volume to standard Hornwort but boasts significantly tighter, denser growth. It is completely rootless, existing as a massive, free-floating, deeply branching aquatic column. The central stem is incredibly thick, highly rigid, and brittle. The foliage consists of extremely narrow, heavily bifurcated (forked), stiff, needle-like leaves that grow in flawlessly symmetrical, dense circular whorls around the central stem. It resembles a prickly, underwater bottle-brush that grows infinitely toward the surface.
Color & Texture: The coloration is the ultimate defining feature of this premium variant. The dense, prickly whorls of needle-like leaves remain a bright, vibrant, light-green. However, the thick central stem that runs directly through the center of the plant turns a breathtaking, profoundly deep, glowing crimson or dark burgundy-red when exposed to strong light. This creates a spectacular, high-contrast candy-cane effect. The texture is notoriously rigid, stiff, and brittle; the plant feels incredibly coarse and scratchy when handled.

Care, breeding and tankmates

Lighting & CO2: It is an extremely fast-growing, adaptable plant, but lighting dictates its spectacular coloration. In low-light tanks, it will survive, but the central stem will lose its crimson pigmentation and revert to a dull brown or green. To unlock the true, intense, glowing red stem that makes the "Mexiko" variant so valuable, it demands absolute, blasting, high-intensity LED lighting. Injecting pressurized CO2 is entirely unnecessary for its survival, but high lighting without CO2 may invite algae; adding CO2 turns its growth rate into an explosive, uncontrollable force.
Nutrition & Substrate: Like standard Hornwort, the "Mexiko" variant is an absolute biological powerhouse. Being completely rootless, it MUST NEVER be forcibly buried deep into thick aquasoil or gravel; burying the thick red stem will instantly cause it to rot and disintegrate. It feeds 100% from the water column. It aggressively absorbs toxic ammonia, heavy nitrates, and massive amounts of iron. To maintain the spectacular crimson-red stems, the water column MUST be heavily dosed with a premium liquid micro-fertilizer that is exceedingly rich in chelated iron.
Water Chemistry: It is incredibly resilient regarding water parameters. It thrives effortlessly in standard heated tropical aquariums (22-28°C). It effortlessly adapts to extreme pH ranges (6.0 - 8.5) and highly alkaline, extremely hard tap water loaded with calcium and magnesium. In fact, like its standard cousin, it prefers harder water. The only requirement is high nutrient availability; if the water is stripped bare of nitrates and iron, the plant will panic, the thick red stem will turn pale, and it will violently shed its green needles.
Space Management & Placement: Due to its rootless nature and massive, sprawling growth rate, the red-stemmed "Mexiko" variant is incredibly difficult to organize in strict aquascapes. It is primarily utilized as a stunning, high-contrast floating plant or wedged lightly behind heavy background driftwood. It serves as an elite, highly aesthetic "nutrient sponge" to prevent algae in newly flooded setups. It is also highly prized by elite shrimp breeders, providing a dense, red-and-green prickly thicket for high-grade Caridina shrimp to hide and forage.
Pruning: Pruning is a relentless, weekly battle when grown under the intense lighting required to maintain its red stems. Because it grows infinitely, it will quickly block light from reaching the lower regions of the aquarium. Do not attempt delicate trimming; simply grab the massive, thick red stems and physically snap them by hand, discarding the excess mass. Every single snapped red fragment will instantly begin growing into a massive, heavily branched new plant.
Risks & Diseases: The "Mexiko" variant is essentially immune to standard aquatic diseases, but it shares the same devastating weakness as standard Hornwort: it is violently, fatally allergic to liquid carbon supplements (like Seachem Excel, Glutaraldehyde) and heavy copper-based medications. Exposure to liquid carbon will cause the entire crimson stem to immediately rot, and the plant will violently shed millions of its stiff green needles, creating a catastrophic, rotting mess across the substrate that can crash the entire tank.

Geographic Origin and Distribution

Endemic primarily to the sun-drenched, nutrient-rich lakes, warm sluggish rivers, and flooded marshes of Mexico and Central America. This specific variant of Ceratophyllum demersum (internationally traded as the "Mexiko" or "Red-Stemmed" Hornwort) is an elite, highly specialized aquatic survivor. It shares the same floating, amphibious lifestyle as standard Hornwort, thriving entirely submerged, but it has evolved under the intense, high-UV solar radiation of the Mexican climate, developing extreme pigmentation to protect its tissues.

Origin

Central America and CaribbeanSelective breeding and cultivars

Plant profile

Placement
Floating
It is highly versatile and can be used as a floating plant to diffuse intense lighting or anchored to hardscape materials. Care should be taken not to plant the stems deep into the substrate, as the lack of true roots will lead to rotting.
Botanical form
Stem
This variant is distinguished by its potential to develop striking reddish or brownish stems under strong light. The needle-like leaves remain dense and bushy, creating a beautiful contrast against the colored stems.
Growth
Fast
It grows very rapidly, though sometimes slightly more compact than the common form depending on lighting. Constant trimming is usually required to manage its vigorous expansion.
Substrate
None
This red-stemmed Mexican variant of Ceratophyllum demersum is a rootless floating aquatic plant that does not require any substrate for healthy growth. It absorbs macro and micronutrients entirely through its foliage directly from the surrounding water column. Aquarists wishing to position it in the background can lightly weigh down the stems in a basic sand or gravel bed. Care must be taken to avoid burying the fragile stems deeply, as they are prone to rotting in anoxic substrate conditions.
Column fertilization
Recommended
Complete reliance on water column fertilization means it benefits greatly from regular dosing of comprehensive liquid fertilizers. Adequate iron dosing can help enhance the attractive reddish hues of its stems.
Root fertilization
None
Root tabs are ineffective for this plant as it lacks a root system for substrate nutrient extraction. All nourishment must be provided via the water column.
Trimming
Occasional
To trim, simply cut the top portions of the stems and remove or replant them. It is important to regularly thin out dense floating mats to ensure sufficient light reaches the lower areas of the tank.
Propagation
Cuttings
It propagates effortlessly by vegetative fragmentation, where any broken stem piece can quickly grow into a full plant. This makes it very simple to multiply and share with other hobbyists.
Sensitivity
Moderate
It shares the same sensitivity to liquid carbon supplements and certain fish medications as the common Hornwort, reacting by dropping its needles. It typically adapts well to a wide range of water parameters but appreciates clean, well-oxygenated water.
Layout role
Midground, Background
The reddish stems make it an interesting focal point when used as a background plant or a floating element. It provides excellent cover for fry and shrimp while adding a subtle splash of color to the upper levels of the aquarium.

Image gallery

Licensed images linked to the species or, when marked, to the closest representative taxon.

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Last updated: 06/30/2026