South American spongeplant
Native to: Mexico to South America
Spongeplant was introduced to the United States as an ornamental pond and aquarium plant. While not currently present in Florida, it was first reported outside of cultivation in California in 2003 where it is listed as a noxious weed and subsequently from one location in Washington State. It is listed as having high invasion risk by the UF IFAS Assessment of Non-Native Plants in Florida’s Natural Areas.
Habit: Perennial aquatic herb, generally free floating but will root in mud in shallow water.
Leaves: Young plants resemble duckweed, then develop into a rosette stage and finally a mature phase with stalked emergent leaves. floating leaves are rounded and have spongy honeycomb-like aerenchymous tissue on the underside.
Flowers: White, inconspicuous monoecious flowers are around 1/2 inch wide and have greenish-white sepals, around 5 mm long by 2 mm wide and spreading. Male flowers have petals and 6 stamens, while female flowers typically do not petals and have 3 to 6 divided styles.
Fruit/Seeds: Soft capsule, about 9 mm long, that forms up to 100 small seeds. Each capsule is on a stem that, after pollination, bends and matures underwater or in mud.
Distribution in Florida: Not present
Reproduces both via seeds which can remain viable for up to 4 years and vegetative production of daughter plants. It spreads through water and wind, on wildlife, and via boats and equipment. It can form thick mats across the water causing problems for boats, native plants and animals, and water infrastructure.
Always clean boats and equipment before leaving a waterway. Never release aquarium water into waterbodies.
Hand removal of all plant material may be effective on small populations.
Choppers and shredders leave fragments which can quickly reestablish infestations.
Grass carp may feed on it but have a preference toward submersed vegetation.
See detailed description in Weed Report from Weed Control in Natural Areas in the Western United States.