Hydrilla
Hydrilla is an introduced plant in Maryland and is therefore considered an exotic species. In fact, the plant is not native to the United States and may have been introduced from southeast Asia through the aquarium trade. The plant is a perennial herb with slender, branching stems forming loose, often impenetrable mats. It is extremely competitive with other plants and can grow in water as deep as 36 feet. In Maryland, it was originally detected in 1982, and since has become one of the major aquatic plant species in the tidal freshwater portions of the Potomac River. Because of its tenacity and varied means of reproduction, it has been considered a noxious plant in many states.