Canadian Waterweed

Young plants initially start with a seedling stem with roots growing in mud at the bottom of the water; further adventitious roots are produced at intervals along the stem, which may hang free in the water or anchor into the bottom. It grows indefinitely at the stem tips, and single specimens may reach lengths of 3 m (9.8 ft) or more. The leaves are bright green, translucent, oblong, 6–17 mm long and 1–4 mm broad, borne in whorls of three (rarely two or four) round the stem. It lives entirely underwater, the only exception being the small white or pale purple flowers which float at the surface and are attached to the plant by delicate stalks. These stalks, or hypanthia, are the lower part of the petals joined to form a floral tube. This floral tube can be up to 30 cm (12 in) in length, while only 1 mm in width, for a length to width ratio of 300 fold. However, according to one article, this ratio can sometimes be as much as one thousandfold. It is dioecious, with male and female flowers on different plants. The flowers have three small white petals; male flowers have 4.5–5 mm petals and nine stamens, female flowers have 2–3 mm petals and three fused carpels. The fruit is an ovoid capsule, about 6 mm long containing several seeds that ripen underwater. The seeds are 4–5 mm long, spindle-shaped and smooth. …

The native range of the species includes most of North America, from British Columbia east to Nova Scotia, south to California, and southeast to northern Florida, in rivers and lakes from sea level up to 2,000 m (6,600 ft) altitude, primarily in lime-rich waters.