Amazon frogbit
Limnobium laevigatum
Also known asSouth American spongeplant · Smooth frogbit · West Indian spongeplant
Water parameters
Light and nutrients
Substrate type: floating. Propagation: runners.
Substrate compatibility
| Substrate | pH effect | Nutrient load |
|---|---|---|
| Bare bottom (no substrate) (Bare bottom) | n/a | none |
| Inert sand (Pool filter sand) | neutral / inert | none |
| Inert gravel (Aquarium gravel) | neutral / inert | none |
| Aquasoil (ADA Amazonia) | lowers pH | very high |
| Mineralized clay substrate (Seachem Fluorite) | neutral / inert | moderate |
| Dirted tank (mineralized topsoil) (DIY soil substrate) | slightly acidic | very high |
| Wood and rock mounts (Hardscape mount) | varies | none |
With fish
Origin and habitat
A free-floating plant of slow and still freshwater across the Neotropics, from Mexico through Central and South America to Argentina and Chile, in oxbows, flooded-forest pools, pond edges and sheltered coves. Long classed as Limnobium laevigatum in the family Hydrocharitaceae, it is also treated under the name Hydrocharis laevigata. It forms rosettes of round, spongy leaves 2–5 cm across that lie on the surface, buoyed by air-filled aerenchyma tissue, with long roots trailing into the water. Under strong light the leaves cup slightly and turn bright green. It spreads fast by stolons that bud daughter plants into dense mats, and also sets seed, and has naturalised as an invasive well beyond its range, including California, Chile, the Iberian Peninsula, Australia, Japan and parts of Southeast Asia.
Outdoor pond use
- USDA zones
- 8–13 (winter low around -12°C or warmer)
Care notes
About as forgiving a plant as the hobby offers. Amazon frogbit strips nitrate, ammonia and even heavy metals from the water column quickly, which is why aquarists drop it into overstocked or freshly cycling tanks as living filtration, and its trailing roots shelter fry and shrimp. Growth is fast under low to strong light, and a single plant can blanket a small surface in a couple of weeks, so the main job is thinning it weekly; left unchecked it shades out everything below. The one weakness is its leaf surface: water sitting on top, from a dripping lid or splashy filter return, rots the leaves, so leave a lid gap and baffle strong outflow or corral the plants behind a length of airline across the surface. Propagation needs no effort, since daughter plants appear on runners; just remove the excess. Nutrient demand is low because it feeds from the water column, though liquid fertiliser helps in very lean tanks. That hunger for dissolved nutrients also makes it a useful floating plant for stripping nitrogen in aquaponics sumps, though it is ornamental rather than edible.