Riccia fluitans

Also known as Crystalwort, Floating crystalwort, Floating liverwort, Riccia

FreshwaterMossCuttings

Invasive. Can form weedy floating mats and is regulated in some regions. Never release into the wild; dispose of in the trash.

Riccia fluitans (Riccia fluitans) — Piotr Kuczynski · CC BY-SA 3.0

Care at a glance

Light: High light
CO2: CO₂ required
Growth rate: Fast
Placement: Floating
Type: Moss
Temperature: 59–86°F (15–30°C)
pH: 6.0–8.0
Hardness: 0–21 dGH
Max height: 1.2 in (3 cm)
Spread: 15.7 in (40 cm)
Nutrient uptake: Water column
Growth region: Submersed or emersed
Difficulty: Medium
Origin: Cosmopolitan (worldwide temperate and tropical fresh waters)
Family: Ricciaceae

Overview

Left to float it is easy and spreads fast, but the showpiece use is pinning a thin layer under mesh or hairnet to hardscape to make a submersed carpet that pearls heavily under strong light and CO2. Submersed Riccia is demanding: it needs high light, pressurized CO2, and regular trimming, and it constantly tries to detach and float free, so it requires more upkeep than typical carpets. It traps fine debris and grows so fast it can shade plants below or clog filter intakes if it escapes. It spreads aggressively and is a recognized weedy/invasive nuisance in some regions, so never release it into local waterways.

In the wild

A cosmopolitan aquatic liverwort found floating in still and slow fresh water across temperate and tropical regions worldwide. In the wild it drifts at the surface as tangled mats; only certain regional varieties (notably the Japanese form) adapt well to growing fully submersed.

Good to know

Despite being grouped with mosses in the hobby, Riccia fluitans is a thalloid liverwort (Marchantiophyta) in the family Ricciaceae, with no true roots, stems, or leaves; the whole plant is a branching, ribbon-like green thallus. It reproduces almost entirely by fragmentation, with each broken piece growing into a new plant.

Did you know

Riccia carpets were popularized by aquascaper Takashi Amano, who pinned the floating liverwort underwater to create the famous shimmering 'pearling' lawns covered in oxygen bubbles, a use the plant never has in nature.