Limnobium laevigatum is a floating aquatic plant and is a member of the family Hydrocharitaceae. Common names include West Indian Spongeplant, South American Spongeplant and Amazon or Smooth Frogbit. This plant was introduced to North American waterways through use in aquariums and aquascapes.
Spongeplant originates from freshwater habitats of tropical and subtropical Central and South America. In California it has been introduced as an ornamental pond plant and has escaped into greater waterways including areas surrounding Redding and Arcata, the Sacramento River delta and the San Joaquin River, and ponds and irrigation canals.
Limnobium laevigatum is a floating aquatic plant, which can be mistaken for water hyacinth (Eichornia crassipes) due to their superficial similarity. Juvenile plants grow in rosettes of floating leaves that lie prostrate upon the water surface, a distinguishing character of the juvenile plant is the presence of spongy aerenchyma tissue upon the abaxial surface (underside) of the leaf. Mature plants grow up to 50 cm tall and have emergent leaves borne on petioles that are not swollen or inflated like the spongy leaf stalks of water hyacinth, which aid in buoyancy. Spongeplant produces stolons that bear gametes. Flowers are small, white, and unisexual. Female flowers have an inferior ovary, the fruit is a fleshy capsule 4 – 13 mm long and 2 – 5 mm in diameter, and seeds are 1 mm long, ellipsoid, and hairy.
Limnobium laevigatum can reproduce and distribute sexually through flower pollination and seed production, and also vegetatively through fragmentation of stolon segments. The juvenile plants have a great capacity for distribution in that they are small, they float and can be easily and quickly carried along by water currents.