Indian Toothcup: Caring for Rotala indica
- aquaterraobsession
- 6 days ago
- 8 min read
Aquarium Plant Care Sheet
:
This article provides information on the care of Rotala indica in the aquarium.
1. Table of Contents
Introduction and Taxonomy
Rotala indica, commonly known as Indian Toothcup, is a unique aquatic stem plant belonging to the Lythraceae family. It is valued in the aquascaping hobby for its strict upright growth habit, compact leaf structure, and vibrant green stems that can turn reddish at the tips under high light.
Important Taxonomic Note: There is significant confusion in the aquarium trade regarding this species. For decades, the popular plant Rotala rotundifolia was erroneously sold under the name "Rotala indica." While R. rotundifolia is a fast-growing, draping plant with narrow submersed leaves, the true Rotala indica is a slower-growing, stiffer plant with round leaves and a vertical structure. This report focuses on the true Rotala indica (often sold as "Rotala Bonsai" or "Ammania sp. Bonsai" to distinguish it from the mislabeled rotundifolia).
Scientific Name: Rotala indica (Willd.) Koehne
Synonyms: Peplis indica, Ameletia indica
Common Names: Indian Toothcup, Rotala Bonsai (trade name)
Family: Lythraceae
Summary Table of Ideal Care Parameters
Parameter | Ideal Range | Notes |
Difficulty | Moderate to High | Requires stable parameters and good light; more demanding than R. rotundifolia. |
Placement | Midground | Its slow, vertical growth makes it excellent for midground transition zones. |
Lighting | High | High intensity is required to prevent lower leaf loss and compact internodes. |
Temperature | 22°C – 28°C (72°F – 82°F) | Tropical temperatures are preferred; avoid sudden drops. |
pH | 6.0 – 7.5 | Prefers slightly acidic to neutral water. |
General Hardness (GH) | 4 – 12 dGH | Soft to moderately hard water is best. |
Carbonate Hardness (KH) | 3 – 8 dKH | Moderate buffering capacity helps maintain pH stability. |
TDS | 100 – 300 ppm | Cleaner water columns often yield better health. |
Water Flow | Moderate | Sufficient flow is needed to deliver nutrients to dense stems but avoid blasting it. |
Substrate | Nutrient-Rich Soil | Active aquasoil is highly recommended for root development. |
CO2 | Essential | High CO2 (20-30 mg/L) is critical for preventing stunting and promoting health. |
Fertilization | Moderate to High | Demands consistent macro and micronutrients; susceptible to deficiencies. |
Growth Rate | Slow | Grows much slower than other Rotala species; rarely needs weekly trimming. |
Propagation | Stem Cuttings | Cut the top stem and replant; susceptible to crushing during planting. |
Compatible Species | Shrimp, Small Tetras | Best with peaceful species that will not uproot delicate stems. |
Maintenance | Low to Moderate | Low trimming frequency, but requires monitoring for algae on slow-growing leaves. |
Common Issues | Stunting, Algae | Tips may stunt without CO2; prone to green spot algae due to slow growth. |
Cultivars | 'Bonsai' (Trade name) | Often sold as Rotala sp. 'Bonsai' or Ammania sp. 'Bonsai'. |
Native Range and Geographic Distribution
Rotala indica is native to tropical and subtropical regions of Asia. Its range is extensive, covering India, Southeast Asia, China, and Japan.
It has also been introduced to rice-growing regions in Europe (such as Italy and Portugal), Africa (Congo), and the United States (specifically California and Louisiana), where it is sometimes classified as an invasive weed in agricultural rice paddies.
Natural Habitat and Environmental Conditions
In the wild, Rotala indica is an amphibious annual plant primarily found in wetlands, shallow marshes, and rice paddies.
Light Exposure: It grows in open, sun-drenched environments with no overhead canopy. It receives full solar intensity, which explains its high light demand in the aquarium.
Substrate: The natural substrate is typically muddy, nutrient-dense silt or clay found in stagnant or slow-moving waters. This soil is rich in organics and iron.
Water Quality: It thrives in shallow, warm water that may fluctuate seasonally. The water is generally soft and acidic, though the plant is adaptable to the variable conditions of temporary water bodies.
Emergence: It naturally spends much of its life cycle in an emersed state (above water) or in very shallow water, flowering when the stem tips break the surface.
Morphological and Growth Characteristics
Rotala indica is distinct from other Rotala species due to its architectural structure.
Stems: The stems are thick, fleshy, and strictly vertical. Unlike R. rotundifolia, which tends to drape or crawl, true R. indica grows straight up like a pillar.
Leaves:
Submersed Form: The leaves are small, round to oval, and arranged in opposite pairs (decussate) along the stem. Under high light, the leaves are densely packed with very short internodes. The color is typically bright green, but the shoot tips can turn orange or reddish under intense light.
Emersed Form: In its terrestrial form, the leaves are obovate (egg-shaped) with a thick, cartilaginous margin. They are generally glossier and more robust than the aquatic leaves.
Root System: It develops a moderate root system. While it feeds from the water column, it relies heavily on roots for stability and nutrient uptake from the substrate.
Flowers: A key identifier for the true species. It produces solitary, tiny pink or reddish flowers in the axils of the leaves (where the leaf meets the stem), rather than on large terminal spikes like other Rotala species.
Ideal Water Parameters
To achieve the compact "bonsai" look that aquascapers desire, strict adherence to water parameters is helpful.
Temperature: 22°C to 28°C (72°F – 82°F). Prolonged exposure to temperatures below 20°C can slow growth to a halt.
pH: 6.0 to 7.5. It prefers the acidic side of neutral.
Hardness: Soft to moderately hard water (4–12 dGH) is ideal. Very hard water may inhibit nutrient uptake and cause tip stunting.
Water Cleanliness: Keep organic waste low. Because it grows slowly, leaves remain on the stem for a long time, making them vulnerable to algae if water quality degrades.
Aquarium Lighting Requirements
Lighting is the single most important factor for the health and aesthetic of Rotala indica.
Intensity: High lighting is mandatory. You should aim for 50–70+ PAR at the substrate level.
Photoperiod: 8 to 10 hours of consistent light daily.
Spectrum: A full-spectrum light (6500K to 8000K) promotes dense vegetative growth. Lights with enhanced red and blue peaks (RGB) can help stimulate the reddish coloration in the shoot tips.
Placement: Place the plant directly under the light source. If shaded by taller plants or hardscape, the lower leaves will deteriorate and fall off, leaving a bare stem.
Substrate and Hardscape Preferences
Rotala indica is a root feeder as well as a column feeder.
Substrate: A nutrient-rich, active aquarium soil (aquasoil) is the best choice. These soils lower the pH and provide essential nitrogen and ammonia to the roots. Inert substrates like sand or gravel can be used but must be supplemented with high-quality root tabs containing iron and macronutrients.
Hardscape: It contrasts beautifully against dark hardscape materials like Seiryu stone or dark driftwood. Its vertical habit makes it an excellent choice for accenting the base of rocks in an Iwagumi layout.
Fertilization and Nutrient Management
Because Rotala indica is a slow grower, it does not strip the water column of nutrients as fast as aggressive stem plants, but it requires consistent availability.
Macros (NPK): maintain stable Nitrogen, Phosphorus, and Potassium levels. Nitrate levels should not hit zero, as this can cause stunting. Aim for 5–10 ppm NO3.
Micros: Iron is crucial for the health of the stem and the coloration of the tips. Dose a comprehensive micronutrient fertilizer regularly.
CO2 Injection: This is often considered non-negotiable for true Rotala indica. Without CO2 injection, the plant will likely lose its lower leaves, grow with large gaps between leaves (leggy), and eventually wither. Maintain CO2 levels at 20–30 mg/L.
Tank Size, Planting, and Placement
Tank Size: Suitable for all tank sizes, including nano tanks (under 10 gallons), due to its small leaf size and slow growth rate.
Placement: Best placed in the midground. Its strict vertical growth creates a perfect transition wall between low foreground carpeting plants and taller background species.
Planting: Use fine-tipped tweezers. Separate the stems and plant them individually or in pairs, spacing them about 1–2 cm apart. Do not bunch them too tightly, as this blocks light to the lower leaves and causes rotting. Be gentle; the stems are fleshy and can be crushed easily.
Maintenance, Trimming, and Pruning
One of the advantages of Rotala indica is its low maintenance regarding trimming.
Trimming Frequency: Low. It grows slowly compared to other stems.
Pruning Method: The best method is "topping." Cut the top 2–3 inches of the stem and replant it. Leave the bottom portion in the soil; it will usually sprout two new side shoots from the cut point, creating a bushier appearance.
Algae Control: Because leaves stay on the plant longer, manually remove any leaves with algae. Use a soft toothbrush to gently clean stems if necessary.
Propagation Techniques
Propagation is vegetative and straightforward.
Stem Cuttings: Simply cut the healthy top portion of a stem and replant it into the substrate. The cutting will root within a few days.
Side Shoots: As the plant matures, it may produce side shoots naturally. These can be snipped off and replanted as independent stems.
Dry Start Method (DSM): Rotala indica is an excellent candidate for the Dry Start Method.
Procedure: Plant the stems in wet aquasoil before flooding the tank. Cover the tank with plastic wrap to maintain 90%+ humidity.
Benefit: The plant will root deeply and establish robust growth without algae issues. Once flooded, it transitions to submersed growth relatively easily, though some old leaves may melt.
Compatibility with Aquatic Species
Rotala indica is safe for all aquatic life, but its delicate structure dictates its tank mates.
Fish: Best suited for small, peaceful schooling fish such as Ember Tetras, Neon Tetras, Rasboras, and Guppies. Avoid large cichlids or goldfish that dig in the substrate or eat plants.
Invertebrates: Ideally suited for shrimp tanks (Neocaridina and Caridina species). The dense, vertical stems provide excellent grazing surface for shrimp. Snails like Nerites are good for keeping the slow-growing leaves clean.
Plants: Pairs well with carpeting plants like Hemianthus callitrichoides 'Cuba' or Monte Carlo. It contrasts well with red plants like Alternanthera reineckii.
Common Cultivation Challenges and Troubleshooting
Stunting/Tip Curling: This is the most common issue. It is usually caused by unstable CO2 levels or a sudden drop in nutrients. Ensure CO2 is consistent and flow is reaching the plant.
Loss of Lower Leaves: Caused by insufficient light penetrating to the bottom of the stem. Increase light intensity or space the plants further apart.
Melting: Often occurs when transitioning from emersed to submersed form. This is normal; remove the melting leaves and focus on the new growth.
Green Spot Algae: Common on older leaves due to slow growth. Increase phosphate levels slightly or improve water circulation.
Varieties and Cultivars
Unlike Rotala rotundifolia, which has dozens of color morphs (H'ra, Green, Orange Juice), true Rotala indica has fewer commercial varieties.
Rotala sp. 'Bonsai': This is the most common trade name for true Rotala indica (or a very close morph of it) in the aquarium hobby. It is characterized by its thick stem and small, round leaves.
Ammannia sp. 'Bonsai': An obsolete trade name. If you see a plant sold as "Ammannia Bonsai," it is almost certainly true Rotala indica.
Commercial Availability and Sourcing
Availability: Less common than R. rotundifolia. It is frequently found in "In-Vitro" (tissue culture) cups, which is the recommended way to buy it. Tissue culture ensures the plant is free of algae and pests.
Sourcing: Look for the specific trade name "Rotala Bonsai" or "Rotala indica (True)" to ensure you are not buying Rotundifolia. If the plant in the shop is draping, has long narrow leaves, and is very red, it is likely Rotundifolia, not Indica.
Conclusion
Rotala indica is a sophisticated choice for the aquascaper looking for structure and order. Its pillar-like growth habit and vibrant green, round leaves offer a unique texture that few other stem plants can provide. While it demands more attention to lighting and CO2 than its common cousins, the result is a striking, architectural stand of plants that resembles a miniature bamboo forest. With patience and stability, it becomes a highlight of the midground in any planted aquarium.
Comments