Limnobium laevigatum ((Humb. & Bonpl. ex Willd.) Heine* (West Indian Spongeplant) is a floating aquatic plant native to Caribbean islands and South America. It has rosettes of floating circular leaves resembling those of a small water lily, emergent leaves, and small white flowers. It was widely sold and planted as an ornamental and aquarium plant in California, Europe, South Africa, and Japan, and Australia. It was first reported from a park pond in Hayward in 1995, but was reported from the Delta by 2010, and by 2017, was reported as a serious invasive plant affecting shipping, fisheries, and wildlife habitat. It is a competitor with the native floating plant, Water Pennywort (Hydrocotyle umbellata), and has replaced it in some areas. Chemical and mechanical control is being used in the Delta, and research on biocontrol agents is underway.
*The current name for this plant is Hydrocharis laevigata (Humb. & Bonpl. ex Willd.) Byng & Christenh. (Royal Botanic Gardens Kew 2024). However, this name in not used by US sources, such as USDA Plants; USGS Nonindigenous Aquatic Species Database, and Flora of North America.