Common names: Amazon frogbit, American frogbit

Family: Hydrocharitaceae

Could be confused with: Eichhornia, Heteranthera, Hydrocharis, Hydrocleys, Limnocharis.

Native distribution: America.

Species commonly cultivated:
Limnobium laevigatum (Willd.) Heine (Central and South America)
L. spongia (Bosc) Steud. (North America)

Adventive distribution: Limnobium laevigatum is introduced into the southern United States.

Weed status: Sometimes considered troublesome. Limnobium laevigatum is a noxious weed in California (United States).

Habit: Free-floating, stoloniferous rosette plant.

Brief description: Perennial, monoecious. Leaves floating or emergent, arranged in basal rosettes along stolons; petiole short or elongate; leaf blade orbicular-obovate to reniform, venation palmate, inconspicuous; base cordate to rounded; margin entire; aerenchyma on abaxial surface distinct; basal sheath present. Flowers unisexual, pedicels short, spathe of 1 or 2 free bracts; female flowers 1 to 3, hypanthium absent; males in cymes of up to 11 flowers; sepals 3; petals 3, rudimentary or absent in female flowers. Dispersal by seed and stem fragments.

Natural habitat: Still waters of lakes, rivers, ponds and swamps.

Additional comments: Limnobium contains only two species, with L. laevigatum being more commonly cultivated for ponds and aquaria. Limnobium spongia is more likely to form emergent leaves than L. laevigatum, which produces emergent leaves only when it becomes crowded.