Limnobium

Scientific name

Limnobium Rich.

Common names

Amazon frogbit, American frogbit

Family

Hydrocharitaceae

Native distribution

America

Species cultivated

Limnobium laevigatum (Humb. & Bonpl. ex Willd.) Heine

L. spongia (Bosc) Steud.

Adventive distribution

Limnobium laevigatum is introduced into various parts of United States.

Weed status

Sometimes troublesome; both Limnobium species are considered weeds in a few countries.

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. Both are highly variable species; leaf shape is important in differentiating the them: L. laevigatum has a more rounded leaf apex, a shallower basal notch, little or no red pigment, and shorter stolons (plants more crowded) than L. spongia. The spongy aerenchyma cells are most prominent on young floating leaves. Older plants and aerial leaves of both species have reduced aerenchyma.