TankBud

American frogbit

Hydrocharis spongia

Also known as Limnobium spongia, American spongeplant, American frog's-bit

FreshwaterFloatingRunners

Invasive. California lists American frogbit as a noxious weed (California Code of Regulations, title 3, section 4500), and it should never be released into the wild.

Care at a glance

Light
Medium light
CO2
No CO₂ needed
Temperature
64–82°F
18–28°C
Max height
5.9 in
15 cm
Growth rate
Fast
Placement
Floating
Type
Floating
pH
5.0–8.0
Spread
5.9 in (15 cm)
Nutrient uptake
Water column
Growth region
Submersed or emersed
Difficulty
Easy
Family
Hydrocharitaceae
Origin
Eastern and southern United States, New Jersey to Florida and west to Texas

Overview

American frogbit is a floating plant for calm water in a freshwater tank. It is easy to keep and grows fast.

Did you know

Bosc named American frogbit Hydrocharis spongia in 1807. Steudel moved it to Limnobium in 1841, and the merger of the two genera has returned it to its first name.

Caring for American frogbit

Float American frogbit on calm water, with no substrate and no added CO2. Its hanging roots feed from the water, so a liquid fertilizer helps in a lean tank. Give it medium light.

Keep the water at 64 to 82°F (18 to 28°C). Flowgrow puts its best growth at 18 to 24°C, cooler than Amazon frogbit, with limits of 4 to 27°C.

Leave an air gap under the lid, since leaves can stand on stalks up to 6 in (15 cm). Keep condensation and filter spray off the leaves, which can rot when they stay wet.

It grows fast and spreads by runners, and the new plants break away to float on their own. Thin the runners often so light reaches the plants below.

Good to know

American frogbit belongs to the family Hydrocharitaceae, and POWO, GBIF and WFO now place the genus Limnobium inside Hydrocharis. Its leaf blades are heart-shaped and 2.5 to 7.5 cm long, with spongy air pockets under the floating leaves. Amazon frogbit has smaller leaves, 2 to 5 cm long and rounded at tip and base. Amazon frogbit's male flowers carry about 6 stamens, against 9 to 12 in American frogbit. Some nurseries sell European frogbit under this name, but its floating leaves lack the spongy pad.

In the wild

American frogbit is native to the eastern and southern United States, from New Jersey south to Florida and west to Texas. It grows in swamps, ponds, bayous and deep ditches where the water is still or barely moving. Plants float free or root in mud along the shore. Northern plants survive winter as starchy buds that sink, while southern plants grow all year.

Common questions

Does American frogbit need to be planted in the substrate?

No. American frogbit floats at the surface and takes its nutrients straight from the water.

Does American frogbit need CO2?

No. American frogbit grows well without added CO2.

How much light does American frogbit need?

American frogbit wants medium light. A light sold for planted tanks covers it.

How do you propagate American frogbit?

American frogbit propagates by runners. New plants form along its runners and break away to float on their own.

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