Elodea nuttallii

Western Waterweed

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The natural history of the northwoods


  • Elodea, from the Greek`eleios (heleios), "of the marsh or meadow"
  • nuttallii, from the Latin, "Nuttall's", after Thomas Nuttall (1786-1859), one of the first naturalists to explore the American West.
  • Common name from its aquatic habitat and general distribution
  • Other common names include: Free Flowered Waterweed, Nuttall's Waterweed, Smalbladet vandpest (Dan), Nuttalls Wasserpest (Ger), Smalle Waterpest (NL), Vodomor Nuttalov (Slovak), Smal 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: 502246
  • Also known as Anacharis occidentalis, Anacharis nuttallii, Elodea columbiana, Elodea minor, Elodea occidentalis, Philotria angustifolia, Philotria minor, Philotria nuttallii, Philotria occidentalis, Udora verticillata var minor


  • A submerged perennial herb
  • Leaves pale green, typically in whorls of 3 or occasionally 4, often recurved with folded margins; lower leaves in pairs and reduced in size. Upper and middle leaves linear to lanceolate, ¼"-½" long, 0.7mm-1.5mm wide, acute at tip; lower leaves ovate-lanceolate.
  • Stem slender, round in cross section, often freely branched, 12"-40" long.
  • Roots white, unbranched, and thread-like. Not always present.
  • Flowers imperfect; male and female borne on different plants.
  • Male Flower spathes solitary, borne in middle leaf axils, sessile, ovoid, about 2mm long. Spathe 2-part but with lobes twisted together making it appear pointed. Flower breaks free from plant and floats to the surface where it opens, allowing pollen to drift on water's surface. Hence the common name of "Free Flowering Waterweed".
    • Sepals ovate, only about 2mm long, sometimes reddish
    • Petals petals lacking or to 0.5mm long, ovate-lanceolate
    • Stamens stamens 9, the inner 3 elevated on a common stalk
  • Female Flower spathes borne in upper leaf axils, linear and narrowly cylindric but slightly broadened at the base and the tip, ¼"-1" long; extending to the surface by a threadlike hypanthium up to 4" long.
    • Sepals green, tiny, obovate, about 1mm long
    • Petals white, obovate, longer than the sepals
    • Stigmas slender, slightly exceeding the sepals
  • Fruit narrowly ovoid to fusiform capsule, 5mm-7mm long, containing several seeds. Ripens underwater.
  • Seed cylindric, 3.5mm-4.5mm long, with long hairs at base


  • A submerged aquatic plant, identifiable as a Waterweed by its short, blunt leaves borne in whorls.
  • Similar to the more common Canadian Waterweed (Elodea canadensis) but smaller and more delicate in such minor detail as:
    • male flower spathes 3/16" or less (vs 5/16" or more), and stalkless
    • styles usually 2 mm or less (vs 4mm)
    • leaves usually less than 1.7 mm wide (vs 1mm-5mm, averaging 2mm)
    • seeds 3.5mm-4.5mm (vs 4.5mm-5.5mm or more)
  • 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.


  • Quebec to Minnesota, the Dakotas, Montana, and Washington, south to North Carolina, Tennessee, Arkansas, Oklahoma, Colorado, Nevada, and California.
  • Also Europe, Asia.


  • Quiet waters of lakes and streams.
  • Typically found in calcareous, "hard" water.





  • By Seed
    • Flowers June-August
    • Male flowers break off plant, rise, 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