Elodea canadensis

Canadian Waterweed

Elodea, Photo © 2001 by Earl J.S. Rook
Photo © 2001 by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Elodea, from the Greek, `eleios (heleios), "of the marsh or meadow"
  • canadensis, from the Latin, "of Canada"
  • Common name from its aquatic habitat and general distribution
  • Other common names include: American Elodea, Anacharis, Canadian Pondweed, Ditch Moss, Water Thyme, …lodée du Canada (Qué), Vandpest (Dan), Kanada vesikatk, vesihain (Est), Vesirutto, Kanadanvesirutto (Fin), Kanadische Wasserpest (Ger), Brede Waterpest (NL), Vasspest (Nor), Vodomor Kanadskż (Slovak), Vattenpest, Vanlig Vattenpest (Swe)


  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Liliopsida, the Monocotyledons
      • Subclass Alismatidae
        • Order Hydrocharitales
          • Family Hydrocharitaceae, the Frog's-bit Family
            • Genus Elodea, the Water Weeds
  • Taxonomic Serial Number: 38937
  • Also known as Anacharis canadensis, Anacharis canadensis var. planchonii, Elodea brandegae, Elodea ioensis, Elodea linearis, Elodea planchonii, Helodea canadensis, Philotria canadensis, Philotria linearis


  • A submerged perennial herb
  • Leaves bright green, typically in whorls of 3 or occasionally 4 (some opposite), spreading to recurved, linear, flat, entire, and 2 to 5 times as long as wide. Whorls compact near growth tip, with spacing between whorls gradually increasing further down the stem. Upper and middle leaves linear-lanceolate (on male plants) or oblong-lanceolate to ovate-lanceolate (on female plants), 3/8"-5/8" long, 1-5 mm wide, mostly more than 1.5 mm wide, round tip, more strongly overlapping on female plants. Lower leaves opposite, reduced, ovate-lanceolate.
  • Stem slender, round in cross section, branching, 8"-40" long. Winter buds appear as short, compact branches in late summer.
  • Roots white, unbranched, and thread-like. Not always present.
  • Flowers imperfect; male and female borne on different plants.
  • Male Flower borne in upper leaf axils, at end of a threadlike, ¾"-12" long stalk, reaching to the surface. Spathes cylindric, about ½" long, inflated up to 3/16" wide.
    • Sepals green, elliptic, about 1/8"-3/16" long
    • Petals white, clawed, linear, about 3/16" long
    • Stamens 9, the inner 3 raised on a common stalk
  • Female Flower borne in upper leaf axils, at end of a threadlike, ¾"-12" long stalk, reaching to the surface. Spathes elongated, cylindric, ¼"-½" long.
    • Sepals 3, green, oblong-elliptic, about 1/8" long
    • Petals 3, white, oblanceolate, about 1/8" long
    • Stigmas 3, 2-cleft, on syles about 3/16" long
  • Fruit an ovoid capsule, about ¼" long containing several seeds. Ripens underwater.
  • Seed fusiform, glabrous, narrowly cylindrical, about 3/16" long


  • A submerged aquatic plant, identifiable as a Waterweed by its short, blunt leaves borne in whorls.
  • Similar to the less common Western Waterweed (Elodea nuttallii) but larger and more robust in such minor detail as:
    • male flower spathes 5/16" or more (vs 3/16" or less); at the end of threadlike stalks (vs stalkless breaking off to become free floating).
    • styles usually 4mm (vs 2 mm or less)
    • leaves usually more than 1.7 mm wide (1mm-5mm, averaging 2mm vs. 1.7mm or less)
    • seeds 4.5mm-5.5mm or more (vs 3.5mm-4.5mm)
  • When in flower:
    • a plant with fully formed, utterly stalkless flowers is a male nuttallii
    • plants having flowers on threadlike stalks over 4" long are male or female canadensis
    • a plant having fully formed flowers raised on threadlike stalks which are all less than 4" long is probably a female nuttallii.
  • When flowers are not present, it's something of a judgement call based upon the somewhat smaller, more delicate structure, and paler green leaves of nuttallii.. There is no shame in simply identifying a plant as Elodea.


  • Nova Scotia to British Columbia, south to North Carolina, Alabama, Arkansas, Oklahoma, Colorado, and California.
  • Introduced in Europe, Asia, Australia.


  • Quiet waters of marshes, lakes, and streams, to depths of 25' or more. Also the Great Lakes.
  • Typically found in calcareous, "hard" water.
  • Often forms large masses.





  • By Seed
    • Flowers June-August
    • Male flowers rise on long stalks and split open, spreading pollen onto the water's surface where it drifts and may, by chance, reach a female flower. Pollination occurs at the water's surface at the whim of wind and wave.
    • Rarely successful
  • Vegetatively
    • By fragmentation of the stem.
    • Most common means of reproduction


  • By division of stem


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Useful as oxygenator in garden ponds, and as shelter for small fishes and aquatic invertebrates.



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Last updated on 26 February, 2004