Rorippa aquatica

Rorippa aquatica (syns. Neobeckia aquatica and Armoracia lacustris), the lakecress or lake cress, is a species of freshwater aquatic flowering plant in the family Brassicaceae. It is found in eastern and central North America, generally in the Great Lakes and Mississippi watersheds. A submerged perennial, it has emergent flowering branches. It is typically found in slow-moving water, such as oxbow lakes. It is used as a foreground aquarium plant, as it is undemanding and very slow-growing....read more on Wikipedia.