Rotala rotundifolia is an aquatic stem plant originating from Southeast Asia, favored by aquarium hobbyists for its rapid growth and aesthetic flexibility. Its appearance is highly variable, with leaf shape and coloration changing in response to environmental conditions. In its emergent form, grown out of water, it has rounded leaves, but once submerged in an aquarium, its leaves become more narrow and lance-shaped.
Ideal Aquarium Conditions
Rotala rotundifolia thrives in a broad temperature range, ideally between 72-82°F (22-28°C), and a pH level from 6.0 to 7.5. While it can tolerate various water hardness levels, it prefers soft to moderately hard water. Maintaining stable water conditions is important, as frequent, drastic changes can stress the plant. An aquarium of at least 10 gallons is recommended to provide adequate space and prevent overcrowding.
Lighting plays a significant role in the plant’s growth pattern. While it can survive in low to moderate light, higher intensity lighting encourages denser, more compact growth. Full-spectrum lighting with a color temperature around 6500K for eight to ten hours daily is ideal. In aquariums with significant water depth, stronger lighting is necessary to ensure sufficient light penetrates to the lower portions of the plant for photosynthesis.
While not strictly required, CO2 injection promotes more robust growth; without it, growth may be slower and less dense. A nutrient-rich substrate, such as aquasoil, provides a strong foundation for its root system, though it can also be grown in sand or gravel with the regular use of root tab fertilizers. Comprehensive liquid fertilizers containing both macronutrients and micronutrients are also important for its overall health and development.
Achieving Vibrant Coloration
The most influential factor is high-intensity lighting; exposing the plant to strong light is the first step in encouraging the production of red pigments. Under lower light conditions, the plant will remain primarily green or develop a yellowish hue.
Beyond lighting, nutrient management is a key component. To enhance reddish tones, nitrate levels should be kept low, ideally below 5 parts per million (ppm). This technique, often called nitrate limitation, stresses the plant in a controlled way that encourages it to produce anthocyanins, the pigments responsible for red and pink colors. Conversely, phosphate levels should be maintained at a detectable level, typically above 1 ppm, to support other metabolic functions.
Supplementing with iron is another important factor for achieving deep, rich reds. Iron is a micronutrient that plays a part in chlorophyll production, but it is also directly involved in the synthesis of red pigments. Regular dosing with a liquid fertilizer that contains chelated iron ensures the plant has the necessary building blocks for this coloration.
Trimming and Propagation
Proper maintenance through regular trimming is needed to shape Rotala rotundifolia and promote the desired aesthetic. When the vertical stems grow tall, they should be trimmed along their top or mid-sections. This pruning encourages the plant to send out lateral shoots from the nodes below the cut, resulting in a much bushier and denser appearance over time. Without regular trimming, the plant can become leggy, with foliage concentrated only at the top.
Propagating this plant is a straightforward process. The cuttings obtained from trimming can be used to create new plants. These trimmed tops, ideally a few inches long, can be planted directly back into the substrate. After removing the leaves from the bottom inch of the stem, the cutting is inserted into the gravel or aquasoil, where it will quickly develop roots and grow into a new, independent stem. This method allows aquarists to easily fill out a background or create thick stands of the plant.
Common Cultivars
Several distinct cultivars of Rotala rotundifolia are available, each offering unique visual characteristics.
- ‘H’ra’ is a variety known for its ability to develop intense orange and pinkish-red hues under high light, with thinner leaves that grow at a downward angle.
- ‘Colorata’ is a popular choice that reliably displays a vibrant pink to deep red color even under slightly less demanding conditions than other red variants.
- ‘Green’ is a cultivar that remains a bright, light green regardless of light intensity or nutrient levels, making it a reliable background plant.
- ‘Blood Red’ is a selectively bred variety that showcases a striking, deep red coloration under optimal conditions.
These cultivars provide aquarists with a palette of colors and growth habits to suit various aquascape designs.