canadensis Rich., common waterweed
Elodea nuttallii (Planch,) St. John, Nuttall's waterweed
These underwater perennial plants sometimes occur as tangled masses in lakes, ponds, and ditches. Individual plants within each species vary in appearance depending on growing conditions. Some are bushy and robust, others have few leaves and weak stems. Both species have long, trailing stems with green, somewhat translucent leaves arranged in whorls of 3 around the stem.
Leaf: Mostly arranged in whorls of 3 (occasionally 4), but sometimes opposite on the lower portions of the stems. Leaves very finely toothed along the edges, but evident only with magnification. Common: 6-15 mm long and 1.5-4 mm wide; leaf tip tapered to a blunt point. Nuttall's: 6-13 mm long and less than 1.5 mm wide; leaf tip tapered to a slender point.
Stem: Long, slender, generally branched. Common waterweed is more sparingly branched than Nuttall's waterweed.
Flower: Often does not produce flowers. Small (8 mm across), white flowers occur at the ends of long, thread-like stalks and have 3 petals and usually 3 sepals. Male and female flowers occur on separate plants, but male flowers are rarely produced. Blooms from July to September. Common: sepals to 5 mm long, petals on male flowers only to 5mm. Nuttall’s: sepals to 2 mm long, petals tiny (0.5mm) or absent. Male flowers detach and become free-floating.
Fruit: Capsules approximately 6 mm long, seeds about 4 mm long, but because of a shortage of male plants, seeds are seldom produced.
Root: Tufts of fibrous roots from nodes along the stem.
Propagation: Stem fragments, overwintering buds, and rarely by seeds.
Importance of plant: Food and habitat for fish, waterfowl, other wildlife. Used in cool water aquariums. Common waterweed is a nuisance in Europe and New Zealand where it is not native.
Distribution: Common: throughout most of the U.S. Nuttall's: occasionally in the Northwest and California. More common in eastern U.S.
Habitat: Lakes, rivers, ponds and ditches. Common: most Washington waters. Nuttall's: fresh to slightly brackish water.
May be confused with: Brazilian elodea (Egeria densa), which has a similar appearance, but has longer leaves in whorls of 4 to 6. Hydrilla (Hydrilla verticillata) which has tubers and spiny leaf edges. Coontail (Ceratophyllum sp.), which has forked, needle-like leaves. Also easily confused with each other. Flower structure and leaf width are the most reliable distinguishing characteristics.
Line Drawings: Elodea canadensis
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.htm