Water lettuce
Pistia stratiotes
Also known asNile cabbage · Shellflower · Water cabbage
Water parameters
Light and nutrients
Substrate type: epiphyte. Propagation: daughter plants.
Substrate compatibility
| Substrate | pH effect | Nutrient load |
|---|---|---|
| Wood and rock mounts (Hardscape mount) | varies | none |
| Inert sand (Pool filter sand) | neutral / inert | none |
| Inert gravel (Aquarium gravel) | neutral / inert | none |
| Bare bottom (no substrate) (Bare bottom) | n/a | none |
| Aquasoil (ADA Amazonia) | lowers pH | very high |
| Mineralized clay substrate (Seachem Fluorite) | neutral / inert | moderate |
With fish
Origin and habitat
A free-floating aroid of the family Araceae, Pistia stratiotes, water lettuce, Nile cabbage or shellflower, the only species in its genus and pantropical in distribution, with an uncertain native origin first described from the Nile near Lake Victoria. It floats as rosettes of thick, pale-green, velvety, ribbed leaves 5–15 cm long, with long feathery roots, up to 30 cm, hanging below to feed and shelter fish. It forms dense surface mats. It is a serious invasive in warm freshwaters worldwide, blanketing ponds, lakes and slow rivers, blocking light, crashing oxygen, breeding mosquitoes and displacing native plants, and as a result it is prohibited as a noxious weed in several US states, including Alabama, California, Florida, Louisiana, Mississippi, South Carolina, Texas and Wisconsin, and in Australia.
Outdoor pond use
- USDA zones
- 8–13 (winter low around -12°C or warmer)
Care notes
An easy floating plant for open-top tanks and warm-climate ponds. It wants moderate to strong light and open air above the surface; it does poorly under a closed hood, where heat and dripping condensation rot the velvety leaves, and excess light yellows them. It is strictly warm-water, thriving around 20–30°C and dying below about 15°C, so it cannot overwinter outdoors in cold climates. Its big feathery roots strip nitrate, ammonia and phosphate from the water, making it an effective nutrient-export and phytoremediation plant, and the roots shelter fry and shrimp; that nutrient appetite makes it genuinely useful in aquaponics, though its invasiveness means it should never reach the wild. It spreads fast by daughter plants on short stolons, one rosette making dozens in a season, so thin it often. Crucially, check local rules first: it is illegal in several US states and in Australia. Where legal, it is an attractive, functional floater for open tanks and ponds.