Indian Swamp Weed Hygrophila polysperma is an extremely invasive weed growing above water and also below. It is a fast-growing and fast-spreading species that out shades and out competes other submersed plants. Most likely introduced through the aquarium trade. Prefers flowing streams, but may be also be found in slow-moving waters and also in lakes. Aquatic leaves opposite, elliptic to oblong to 4 cm long. The leaves on stems above water are smaller, narrower and darker. Flowers are bluish-white to white, and have two lips. They grow from the axils where the leaves meet the stems. The fruit is a capsule to 9 mm long covered with hairs especially near the top. Hygro means moist, phil loving, poly many, sperma seed, that is, a wet-loving plant with a fruit that contains many seeds.
Photo: Robert Whyte