Amazon Frogbit (Limnobium laevigatum) is one of my favorite aquarium plants. It has thick, waxy leaves with a spongy underside that grow to a bit bigger than the size of of a US quarter. These leaves are full of tiny compartments containing air, which allows them to float on the water surface. Each plant produces a number of round leaves and long, spindly roots that reach down into the water column. If the water is shallow enough, the roots will reach to the substrate, anchoring it in place.
Care Level: Easy
Preferred Water: 6.0 – 7.5 pH – Soft to Moderately Hard
Minimum Lighting: Medium
Temperature: 64 to 84 °F (18-29 °C)
Maximum Size: Outdoors, 20 Inches (51 cm), Indoors 5 to 6 inches (~13.5cm)
This plant is native to Central and South America, and can be found in warm, slow-moving bodies of freshwater. It is an invasive species in places like California.
Frogbit produces horizontal runners just under the water surface. Daughter plants will set down their own roots, and will eventually break away from the mother plant. It can also produce small aerial flowers, but it is unlikely that this will be a means of propagation in the aquarium environment.
In the Aquarium
Being a fast-growing floating plant, frogbit inevitably will cover the surface of your aquarium. Some species of fish like Bettas and Gouramis will appreciate the overhead cover. Fish fry also benefit by finding shelter among the roots. Because it grows so thickly, it may smother a poorly aerated tank by not allowing sufficient gas exchange at the surface. I like to keep a small flow of air bubbles to help with this. It’s thick, waxy leaves create a lot of shade, and may stunt the growth of plants beneath it.
Frogbit is a relatively easy plant to keep in an aquarium. It does very well in an open-topped setup, but can also prosper in a closed one provided there is enough space between the water surface and the lid to allow ventilation. It thrives in bright light, and will pair well with low light plants, since it blocks so much light from penetrating the surface.
This floating plant cannot survive its leaves being completely submerged for long. A leaf will wither and die if held underwater. Some snails will eat the soft spongy material underneath the leaves. In my tanks, Ramshorn Snails often chew on the leaves. Luckily this plant grows so quickly that it doesn’t matter too much. You will likely have to thin the plant out yourself every other week.
Frogbit as an Invasive Species
Unlike European Frogbit (Hydrocharis morsus-ranae), it is not considered an invasive species in temperate climates. It simply does not tolerate frigid temperatures. With that said, you should always check your local and state regulations about owning this kind of plant, as it is incredibly prolific. It can quickly spread over a body of water, preventing other plants from receiving adequate light.
Like any aquarium plant or critter, do not dispose of this plant in the wild. Always give it to another hobbyist or destroy it.