Scarlet Temple: Caring for Alternanthera reineckii
- aquaterraobsession
- Feb 17
- 8 min read
Aquarium Plant Care Sheet
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This care sheet provides all information required to successfully nurture Ambulia, providing details on its requirements, from light and substrate to propagation and placement.
Table of Contents
Introduction and Taxonomy
Alternanthera reineckii, commonly known as Scarlet Temple or simply AR, is a perennial aquatic plant belonging to the Amaranthaceae family. It is one of the few stem plants in the freshwater aquarium hobby that offers true, vibrant red coloration on the undersides of its leaves, making it a staple for aquascapers looking to create contrast against green foliage.
Taxonomically, the plant is classified as follows:
Kingdom: Plantae
Order: Caryophyllales
Family: Amaranthaceae
Genus: Alternanthera
Species: Alternanthera reineckii
Unlike many other aquatic plants that are strictly submerged, A. reineckii is amphibious. It has adapted to life on land and underwater, a trait that stems from its natural environment where water levels fluctuate drastically. Its ability to retain its red pigment submerged has made it a popular choice for Dutch-style aquascapes and high-tech Nature aquariums.
Summary Table of Ideal Care Parameters
Parameter | Ideal Range | Notes |
Difficulty | Medium | Requires stable parameters and good lighting. |
Placement | Midground to Background | 'Mini' cultivars can be used in the foreground. |
Lighting | Medium to High | 40+ PAR is minimum; 100+ PAR for best color. |
Temperature | 23°C – 28°C (73°F – 82°F) | Avoid extremes above 30°C. |
pH | 6.0 – 7.0 | Prefers slightly acidic to neutral water. |
General Hardness (GH) | 4 – 12 dGH | Needs calcium and magnesium for structure. |
Carbonate Hardness (KH) | 2 – 10 dKH | Moderate buffering capacity is preferred. |
TDS | 130 – 250 ppm | Thrives in clean but mineralized water. |
Water Flow | Low to Moderate | Gentle circulation to deliver nutrients/CO2. |
Substrate | Nutrient-Rich | Active aquasoil is highly recommended. |
CO2 | 20 – 30 ppm | Highly recommended for density and color. |
Fertilization | High | Heavy root feeder; requires Iron and Potassium. |
Growth Rate | Slow to Moderate | Slower than many green stem plants. |
Propagation | Cuttings | Cut stem tops and replant. |
Compatible Species | Tetras, Shrimp, Rasboras | Avoid herbivorous fish like Goldfish. |
Maintenance | Weekly | Prune to prevent shading of lower leaves. |
Common Issues | Algae, Melting, Pinholes | Pinholes indicate Potassium deficiency. |
Cultivars | 'Mini', 'Rosaefolia', 'Rosanervig' | Various sizes and patterns available. |
Native Range and Geographic Distribution
The species is native to the tropical and subtropical regions of South America. Its range spans across Brazil, specifically the Amazon basin and southern states like Rio Grande do Sul, extending into Paraguay, Bolivia, and northern Argentina.
This wide distribution allows the plant to adapt to a variety of climates, though it generally remains within warm, humid zones. It has also been introduced to other regions globally through the aquarium trade, occasionally appearing as an escapee in waterways in warmer climates.
Natural Habitat and Environmental Conditions
In the wild, Alternanthera reineckii inhabits the margins of rivers, streams, marshes, and floodplains.
Hydrology and Water Quality: It is typically found in clear-water streams or "igarapés" that have high transparency and low suspended sediment. The water in these regions is often soft and slightly acidic due to organic decomposition. The plant prefers slow-moving currents that provide constant fresh water without the physical stress of high velocity.
Light Exposure: Because it grows on riverbanks and in shallow waters, the plant receives intense solar radiation. During the dry season, it is often fully exposed to direct sunlight. When submerged during the rainy season, the clear water allows significant light penetration, which drives the production of its red protective pigments (anthocyanins).
Natural Substrate: The substrate in its native habitat usually consists of fertile, alluvial clay or mud rich in iron and organic matter. This explains the plant's strong preference for nutrient-rich substrates in the aquarium rather than inert sand or gravel.
Morphological and Growth Characteristics
Alternanthera reineckii exhibits heterophylly, meaning its physical form changes significantly depending on whether it is growing above or below water.
Submersed Form (Underwater)
Stem: The stems are flexible and fleshy, ranging from green to deep red.
Leaves: Leaves are decussate (arranged in opposite pairs). They are lanceolate to elliptic in shape. The upper (adaxial) surface ranges from olive-green to reddish-brown, while the underside (abaxial) is a vivid pink, purple, or ruby red. This bicolor adaptation helps the plant capture reflected light from the substrate.
Growth Habit: It grows vertically toward the light. Without pruning, it can breach the surface, but in the aquarium, it is usually managed as a bush.
Emersed and Emergent Form (Above Water)
Stem: The stems become more rigid and lignified (woody) to support the plant against gravity.
Leaves: The leaves become smaller, thicker, and covered in a waxy cuticle to prevent dehydration. They are typically solid green or olive and lack the intense transparency and red coloration of the submersed form.
Root System: It develops a robust, fibrous root system. In the water, it also produces adventitious roots from stem nodes, which aid in nutrient uptake from the water column.
Flowers: The plant produces small, inconspicuous sessile flower heads in the leaf axils. The flowers are bisexual (containing both male and female parts) with 5 tepals and 2-5 stamens. They are typically whitish or pale straw-colored.
Ideal Water Parameters
To maintain healthy foliage and prevent melting, water parameters should be kept stable.
Temperature: 23°C to 28°C is the sweet spot.
pH: A range of 6.0 to 7.0 is ideal. The plant struggles in highly alkaline water.
Hardness: It prefers soft to moderately hard water (GH 4-12). Sufficient Calcium and Magnesium are required to prevent leaf curling.
TDS: A Total Dissolved Solids range of 130 to 250 ppm typically indicates a good balance of minerals and fertilizers without excessive waste buildup.
Aquarium Lighting Requirements
Lighting is the single most critical factor for coloration.
Light Intensity: Alternanthera reineckii requires medium to high light. A PAR (Photosynthetically Active Radiation) value of at least 40-50 umol/m²/s is needed for survival, but 100+ PAR is recommended for deep red coloration and compact growth.
Spectrum: A full-spectrum light with a strong emphasis on the red and blue wavelengths is beneficial. The red spectrum promotes photosynthesis, while the blue spectrum stimulates the production of anthocyanins (red pigments).
Photoperiod: Provide 8 to 10 hours of consistent light daily.
Placement: Place the plant directly under the light source. Avoid shading it with taller plants or floating plants, as the lower leaves will deteriorate quickly in shadow.
Substrate and Hardscape Preferences
Substrate: This species is a heavy root feeder. It should be planted in a nutrient-rich, clay-based aquasoil (active soil). If using inert sand or gravel, the use of quality root tabs containing iron and macronutrients is mandatory for long-term success.
Hardscape: It pairs well with dark hardscape materials like Seiryu stone or dark driftwood (e.g., Horn Wood), which visually contrast with the plant's bright red leaves.
Fertilization and Nutrient Management
A comprehensive fertilization regime is necessary.
Macronutrients:
Nitrogen (N): Maintain Nitrate levels between 10-20 ppm. Unlike some plants that redden with nitrate limitation, A. reineckii requires ample nitrogen to maintain leaf structure.
Phosphates (P): Keep between 0.5-1.0 ppm to control spot algae.
Potassium (K): This is crucial. A. reineckii is a "potassium hog." Deficiency shows up quickly as pinholes in older leaves. Dose generously.
Micronutrients: Iron (Fe) is essential for color and health. Dose chelated iron to maintain 0.1-0.5 ppm in the water column.
CO2: While it can survive in low-tech tanks, CO2 injection (20-30 ppm) is required for the plant to thrive, grow dense, and exhibit its famous scarlet color.
Tank Size, Planting, and Placement
Tank Size: Minimum 10 gallons (40 liters) for 'Mini' varieties; 20 gallons or larger for standard varieties like 'Rosaefolia'.
Planting: Plant stems individually with tweezers, spacing them about 2-3 cm apart. Do not bunch them too tightly, as this prevents light and flow from reaching the lower leaves, causing them to rot.
Placement:
'Mini' Cultivar: Foreground to Midground.
Standard Cultivars: Midground (if trimmed) or Background. They are best used to create "streets" or focal points using the Golden Ratio.
Maintenance, Trimming, and Pruning
Regular maintenance is required to keep the bush dense.
Trimming: When stems reach the surface or become too tall, perform a "top cut." Cut the top 4-6 inches of the stem.
Replanting: For the best aesthetic, uproot the old bottom portion (which often becomes woody and bare) and replant the fresh, colorful top cutting. This keeps the colony looking young and vibrant.
Pruning Side Shoots: If you cut a stem and leave the bottom rooted, it will split into two new shoots. This can be done to increase density, but eventually, the crowding will require the replanting method mentioned above.
Propagation Techniques
Propagation is strictly vegetative in the aquarium.
Stem Cuttings: Simply cut the stem, remove the bottom pair of leaves to expose the node, and insert it into the substrate. Roots will form from the buried node within days.
Dry Start Method (DSM): A. reineckii is an excellent candidate for the Dry Start Method.
Fill the tank with substrate and wet it until saturated, but do not flood the tank (water level should be just below the substrate surface).
Plant the stems or tissue culture portions.
Cover the tank with plastic wrap to maintain 100% humidity.
Provide 10-12 hours of light.
Allow plants to root and spread for 4-6 weeks before flooding. This establishes a robust root system without algae issues.
Compatibility with Aquatic Species
Fish: Safe with most community fish.
Ideal: Neon Tetras, Cardinal Tetras, Rummy Nose Tetras, Rasboras, Guppies, Otocinclus.
Avoid: Goldfish, Cichlids (which dig), and large Plecos (which may uproot or crush stems).
Invertebrates:
Ideal: Neocaridina shrimp (Cherry Shrimp) and Caridina shrimp. They keep leaves clean of biofilm.
Caution: Amano Shrimp (Caridina multidentata) have been known to eat A. reineckii leaves if they are starving or if the leaves are melting/soft. Ensure Amano shrimp are well-fed.
Plants: Combines well with bright green plants for color contrast, such as Lobelia cardinalis, Bacopa caroliniana, or Micranthemum 'Monte Carlo'.
Common Cultivation Challenges and Troubleshooting
Melting: New plants often melt when transitioning from emersed (farm) to submersed (tank) growth.
Solution: Remove rotting leaves, maintain high oxygen and CO2, and be patient. New shoots will appear.
Algae (BBA/GSA): The slow growth rate makes older leaves prone to Black Beard Algae and Green Spot Algae.
Solution: Stabilize CO2 levels, increase flow, and ensure phosphate levels are adequate.
Leaf Drop: Lower leaves falling off.
Solution: The plant is shading itself. Space stems further apart or increase light intensity.
Pinholes: Small holes in older leaves.
Solution: Potassium deficiency. Increase Potassium dosage immediately.
Leggy Growth: Long spaces between leaves.
Solution: Insufficient light. Increase PAR.
Varieties and Cultivars
A. reineckii 'Mini': The most popular modern cultivar. Stays short (10-15 cm), deep red/purple, ideal for foregrounds and nano tanks.
A. reineckii 'Rosaefolia' (Pink): The classic variety. Taller, olive-green top with pink undersides. Good for backgrounds.
A. reineckii 'Rosanervig' (Variegated): Features distinct white or light pink veins on the leaves. Often sold as a tissue culture. Very striking pattern.
A. reineckii 'Lilacina': Displays darker, purple-lilac hues and grows larger with broader leaves. Requires more space.
A. reineckii 'Cardinalis': A larger variety with deep crimson coloration, suitable for large aquariums.
Commercial Availability and Sourcing
Pot/Bunch: Commonly available in bunches held by lead weights or in rockwool pots. These are usually grown emersed and will require a transition period.
Tissue Culture (In-Vitro): Highly recommended. These are grown in sterile gel cups. They are free from snails, algae, and pests. Although smaller initially, they adapt faster to submersed conditions and offer a high plant count per cup.
Sourcing: Available at most specialized local fish stores (LFS) and major online retailers. Look for healthy stems that are not mushy or smelling of rot.
Conclusion
Alternanthera reineckii is a jewel of the planted aquarium hobby. While it demands more attention than beginner plants—specifically regarding light, substrate, and CO2—it rewards the aquarist with a display of crimson and magenta that few other species can match. By understanding its natural history as a riverbank dweller and meeting its needs for root nutrition and high light, any aquarist can successfully cultivate this "Scarlet Temple" to create a breathtaking underwater landscape.
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