Amazon frogbit (Limnobium laevigatum): grower data and range

What the grower data says

Tropica rates Amazon frogbit easy, with low light and CO2 demand and medium growth ^[1]. Aquasabi rates it easy too, but calls growth “very fast” and light medium, with no need for added CO2 and water up to “medium” hardness ^[2].

Tropica’s height of 3–5 cm refers to the leaves above the water line. Its description says the plant is 1–5 cm tall ^[1].

A floating nutrient gauge

The most useful line in Tropica’s description is about nutrients: when the nutrient level in the water decreases, the plant grows much more slowly, “which makes it a great indicator of the available nutrients” ^[1]. Conversely, with enough nutrients and good light, new leaves rise above the water surface ^[1]. A frogbit layer that suddenly stalls is therefore a cue to check dosing; the nitrogen, phosphorus and potassium guide covers the main nutrients.

Placement and shade

Aquasabi lists it as a water-surface plant ^[2]. Tropica says it is particularly suitable for open-topped aquariums and also works in conventional ones ^[1]. The cost of a floating plant is light below: Tropica warns that it may become necessary to remove some plants so that those underneath still get light ^[1]. Thinning the cover regularly is part of keeping it.

Names and taxonomy

The trade name Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine is a synonym in the World Checklist of Vascular Plants. WCVP accepts Hydrocharis laevigata (Humb. & Bonpl. ex Willd.) Byng & Christenh., a combination published in 2018, in the frogbit family Hydrocharitaceae, and lists 13 species-rank synonyms. The oldest, Salvinia laevigata Humb. & Bonpl. ex Willd., placed it in a genus of floating ferns ^[6].

WCVP’s native range covers Mexico, Central America, the Caribbean and much of South America, from Venezuela and Colombia to Chile, Argentina and Uruguay ^{[6, 7]}. Tropica’s origin field says “South America” ^[1]. The checklist also records the species as introduced in 16 regions, including California, Belgium, France, Hungary, the Netherlands, Poland, Spain, Sweden, Japan, Java, Taiwan, New South Wales, Queensland, Western Australia, Zambia and Zimbabwe ^[6].

A floating plant recorded as introduced on five continents is exactly the kind that must not leave the tank. California lists it as a noxious weed with an “A” pest rating, which means it may not be brought into the state without a CDFA or USDA permit for contained exhibit or research, and plants found there are subject to state eradication or other control ^{[3, 4]}. Washington lists it as a Class A noxious weed and on its quarantine list, which prohibits transporting, buying, selling or distributing the plant into or within the state ^[5]. Never put surplus plants into ponds, drains or waterways, and check whether the species is regulated where you live; see invasive aquarium plants and safe disposal.