Ceratophyllum demersum

Coontail (Ceratophyllum demersum) is an invasive plant.

Coontail is a dark olive-green, rootless submerged perennial plant that often forms dense colonies and is noted for prolific growth. The tips of branches are crowded with leaves giving it a "coontail" resemblance. This plant is native to the United States but can become a nuisance weed.