Elodea canadensis
Elodea canadensis is a perennial aquatic plant, or submergent macrophyte, native to most of North America. It has been introduced widely to regions outside its native range.
Distribution
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 altitude, primarily in lime-rich waters.Description
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 or more.The leaves are bright green, translucent, oblong, 6–17 mm long and 1–4 mm broad, borne in whorls of three 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 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 thousand fold.
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. It flowers from May to October.
It grows rapidly in favorable conditions and can choke shallow ponds, canals, and the margins of some slow-flowing rivers. It requires summer water temperatures of 10–25 °C and moderate-to-bright light levels.
It is closely related to Elodea nuttallii, which generally has narrower leaves under 2 mm broad. It is usually fairly easy to distinguish from its relatives, like the Brazilian Egeria densa and Hydrilla verticillata. These all have leaves in whorls around the stem; however, Elodea usually has three leaves per whorl, whereas Egeria and Hydrilla usually have four or more. Egeria densa is also a larger, bushier plant, with longer leaves.