The Collaborative International Dictionary
Limnobium Spongia
frogbit \frog"bit`\, frog's-bit \frog's-bit\, n. (Bot.)
A European plant ( Hydrocharis Morsus-ran[ae]), floating on still water and propagating itself by runners. It has roundish heart-shaped leaves and small white flowers.
An American plant ( Limnobium Spongia), with similar habits.