Riccia fluitans

Riccia fluitans is a cosmopolitan floating liverwort found in ponds, ditches, and slow streams worldwide. It lacks roots, stems, and leaves in the traditional sense; instead, the plant body consists of repeatedly forking, ribbon-like thalli that interweave into dense, spongy mats that float on or just below the water surface. The thalli are bright, vivid green and under high light and CO2 injection produce spectacular pearling — visible streams of oxygen bubbles rising from the plant, a signature of healthy, photosynthetically active Riccia in the Nature Aquarium style. The legendary aquascaper Takashi Amano popularized the use of Riccia as a submerged foreground carpeting plant by tying portions of the mat to flat stones or mesh and allowing it to cover the surface in lush green mounds. However, Riccia does not root to surfaces; it must be tied, weighted, or kept behind a mesh, and portions will continuously break free and float to the surface. This behavior requires periodic maintenance in aquascape contexts. As a pure floating plant it is effortless — simply place it on the surface and thin as needed. The mats provide outstanding shelter for fish fry, shrimp, and small invertebrates, and the interlocking structure makes an excellent egg-laying substrate for species like killifish and bubble-nest builders. Riccia is sensitive to prolonged full submersion without mesh support, as inner portions of dense mats may die and cause the mat to decompose from the inside. Moderate to high light and CO2 supplementation are recommended for the most vigorous growth.

Water Parameters Riccia fluitans tolerates pH 6.0–8.0 and temperatures of 15–28 °C. It adapts to soft or moderately hard water. Avoid extreme alkalinity above pH 8.5, which causes yellowing.

Lighting Moderate to high light (50–200 µmol) is recommended. Under high light with CO2 supplementation, Riccia produces prolific pearling and grows rapidly. Under low light, growth slows and the thalli become pale.

CO2 Supplementation While not strictly required, CO2 injection greatly enhances growth rate, thallus density, and oxygen production. Even floating at the surface, dissolved CO2 in the water benefits the plant.

As a Floating Plant Simply place Riccia mats on the water surface and allow them to spread. Thin regularly to prevent excessive coverage. The mats can be scooped out, excess removed, and a portion returned to the tank.

As a Carpeting Plant (Amano Style) Tie small bunches of Riccia to flat stones or attach to a grid of mesh weighted to the substrate. The plant will grow out and over the structure forming a green mound. Every 2–3 weeks, trim the mound back and remove detached floating portions. Pieces will inevitably escape to the surface; net these out regularly.

Common Problems Browning or decomposing inner portions of dense mats indicate insufficient light penetration or anaerobic pockets within the mat. Keep mats thin and regularly thinned. Yellow thalli indicate nitrogen or iron deficiency.