Rotala rotundifolia (Rotala rotundifolia)

Overview of Rotala rotundifolia

Rotala rotundifolia (family Lythraceae) is a fast-growing, amphibious stem plant native to wetlands and paddies across tropical and subtropical Asia. It is one of the most popular stem plants in the aquarium hobby and a reliable vertical accent in wabi-kusa and paludarium builds. Because it naturally lives through flooded and exposed seasons, it switches readily between submerged and emersed life. Trade names are often confused: stock sold as Rotala 'Indica' or 'H'ra' may be a different species or cultivar, so treat the care parameters below as applying to plants commonly sold as Rotala rotundifolia. For the full build process see how to make a wabi-kusa.

Emersed (Terrestrial) Form

Grown above water, Rotala rotundifolia produces thicker, rounder to oval, glossy leaves on upright stems 8-20 cm tall, often with a bronze to pink tint under strong light. This is the form you want for wabi-kusa. It roots readily from the nodes, but it needs 85-95% humidity for the first 3-4 weeks after planting and 70-90% afterwards for compact growth. Under strong light and stable conditions, emersed plants may produce small pink flower spikes.

• Light: 6500K full-spectrum LED at roughly 80-150 PPFD for 8-10 hours daily. Too much light dries the substrate surface quickly.
• Substrate: aquasoil, akadama and coir (for example 60/30/10 by volume). See the wabi-kusa substrate recipe for variations.
• Water: a 1-2 cm reservoir of dechlorinated or RO water that wicks upward; keep the substrate damp, never dripping.
• Temperature: 20-28°C (68-82°F), tolerating 15-32°C.

Submerged Form

Underwater, the plant produces narrow, linear to lance-shaped leaves in whorls along tall, slender stems. It is easy in low-tech tanks, where it stays green to light pink, but vivid pink to red tops need medium to high light (about 50-100 PPFD at the substrate), chelated iron, a nutrient-rich substrate and ideally CO2. Plant loose groups of 5-8 stems 2-3 cm apart, remove the lowest leaves from the buried section and top the stems every 2-3 weeks so light reaches the lower growth.

Converting Between Emersed and Submerged

Rotala rotundifolia changes leaf shape when the growing medium changes, so some melt-back is expected.

1. Submerged to emersed: plant trimmed stems into moist substrate and keep humidity at 85-95% with a lid. Old narrow leaves melt within 1-3 weeks, followed by rounder emersed leaves from the nodes.
2. Emersed to submerged: plant trimmed stems in groups, flood slowly and provide good light. The emersed leaves yellow and drop, and narrow submerged leaves form over 2-4 weeks.
3. Tip: buying plants already grown in the form you want (emersed for wabi-kusa, submerged or tissue culture for tanks) shortens the transition considerably.

Using Rotala rotundifolia in Wabi-Kusa

Place Rotala off-centre on the top or rear of the ball as the vertical focal point, with a creeping filler such as Hydrocotyle tripartita around the base and an epiphyte such as Anubias nana attached to the sphagnum wrap or a stone. Keep the palette to 2-4 species and trim the stems regularly so they do not shade the carpet. Check the wabi-kusa plants guide for further species and the lighting and humidity guide for environmental targets.

Colour: How to Get Pink and Red Rotala

Red colouration is a response to light and nutrients. To encourage it, provide the upper end of the light range (120-150 PPFD emersed, or 80-100 PPFD submerged), keep iron and trace elements available, avoid high nitrogen and add CO2 in submerged tanks. Emersed stems usually show warmer bronze to pink tints than submerged ones. If the stems stay green, check light distance and iron first.

Propagation

Propagation is simple: cut a stem with at least 2-3 nodes and push the base 1-2 cm into moist substrate. Roots form at the nodes within 1-2 weeks, and side shoots develop after pinching. Tops cut during pruning can be replanted immediately, so every trimming becomes a new plant. Lateral shoots can also be removed and replanted.

Pruning and Maintenance

• Pinch emersed stem tips every 2-3 weeks to prevent stretching and encourage side shoots.
• Top submerged stems every 2-3 weeks and replant the tops in groups.
• Remove yellow or melting leaves promptly to prevent mold in humid containers (see the mold prevention guide).
• Replace reservoir water every 1-2 weeks and fertilize lightly once the aquasoil is depleted (about 2-3 months).

Vivarium and Paludarium Integration

In paludariums and humid vivaria, Rotala rotundifolia grows well at the waterline and on the land portion in moist substrate, where it tolerates splashing and shallow flooding. In enclosed setups, ensure good airflow and prune dense stems so the lower layers do not rot. Do not release it into warm outdoor ponds or waterways, where it can escape and become invasive, and check local regulations.

Troubleshooting Summary

Related Resources

Build with it in our wabi-kusa tutorial, choose companion species in the wabi-kusa plants guide, mix the medium with the substrate recipe and dial in conditions with the lighting and humidity guide. Companion plant profiles: Hydrocotyle tripartita and Anubias nana.