Water lettuce: the big-rooted floater
Pistia stratiotes
A velvety floating rosette with long, fry-sheltering roots.
Where it comes from
Pistia stratiotes floats on still and slow tropical fresh water around the world, forming drifting colonies of pale green rosettes. It is so vigorous that it is classed as an invasive weed in many warm regions and is restricted or banned in parts of the United States and Australia — check your local rules and never release it outdoors.
What to expect
Each plant is a rosette of thick, velvety, ridged leaves that genuinely resembles a floating open lettuce. Beneath hangs a dense curtain of long, feathery roots — often longer than the leaves are wide — which is the plant's real gift to an aquarium: superb cover for fry and shrimp and a huge surface for beneficial bacteria.
How to keep it
Water lettuce is easy given two things: decent light and open space above the water. It feeds on tank waste and pulls nitrate down quickly. Daughter plants bud off on short runners, so a couple of rosettes soon become a raft.
| Parameter | Value |
|---|---|
| Lighting | Medium to high — compact under bright light |
| CO2 | Not required; draws CO2 from the air |
| Temperature | 20–30 °C |
| pH | 6.5–7.5 |
| Hardness | Soft to hard |
| Fertiliser | Iron and trace elements help |
| Substrate | None — floats |
| Growth rate | Fast |
| Placement | Floating |
| Difficulty | Easy |
Where it works and how to control it
Give it an open corner and thin it weekly so it never covers the whole surface — plants below still need light. A floating ring or a length of airline tubing pinned in a loop will keep it corralled away from filter outflows.
What goes wrong
The commonest killer is water on the leaves. Droplets from a tight, condensation-heavy lid, or spray from the filter return, sit in the velvety crown and rot it — the rosette goes translucent and collapses. Leave a gap under the lid for airflow and keep the surface calm. Yellowing centres usually signal a shortage of iron.
More plants in this series
- Amazon frogbit (Limnobium laevigatum) — the smaller lidded-tank floater
- Duckweed (Lemna minor) — the tiny relentless floater
- Red root floaters (Phyllanthus fluitans) — the colourful nano floater
- Water sprite (Ceratopteris thalictroides) — lacy fern, plant it or float it