Bacopa rotundifolia is a species of water hyssop known as the disk water hyssop or round-leafed water hyssop, due to the shape of its leaves. This is an aquatic plant native to water bodies of the central United States and well-known in other areas as an invasive weed of waterways. The round leaves are 1 to 3 centimeters wide and each has six longitudinal veins. The plant produces yellow-throated white flowers.
