Hydrocharis spongia

Hydrocharis spongia, also known as Limnobium spongia, and commonly known as the American frogbit or the American spongeplant, is a species of flowering plant in the family Hydrocharitaceae. It is native to the central and southeastern United States, where it grows in the Lower Mississippi Valley as far north as Illinois, and on the Southern Coastal Plain from Texas to Delaware. It is occasionally found elsewhere as a waif. It grows in the slow-moving water of streams, bayous, and lakes from sea level up to 100 meters elevation....read more on Wikipedia.