Isoetes lacustris

Lake Quillwort

Lake Quillwort, Photo Courtesy USDA Plants Database
Lake Quillwort
Photo Courtesy USDA Plants Database

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The natural history of the northwoods


  • Isoetes, from the
  • lacustris, from the Latin lacus, "lake", and ustris, "origin or habitat"; hence, "of lakes"
  • Common name from this plant's pointed form and its preferred habitat
  • Other common names include: Merlin's-grass, Quillwort (UK), Sortgrøn Brasenføde (Dan), Tummalahnanruoho (Fin), Stinnur álftalaukur (Is), See-Brachsenkraut (Ger), Stivt Brasmegras (Nor), Poryblin jeziorny (Pol), Styvt Braxengräs, Braxengräs, Braxenmat, Vårtsporigt Braxengräs (Swe)


  • Kingdom Plantae, the Plants
  • Subkingdom Tracheobionta
    • Division: Lycopodiophyta,
      • Class Lycopodiopsida
        • Order Isoetales, the Quillworts
          • Family Isoetaceae, the Quillworts
            • Genus Isoetes, the Quillwort
  • Taxonomic Serial Number: 17131
  • Also known as: Isoetes hieroglyphica, Isoetes macrospora
  • Quillworts are considered by some to be the last remnant of the fossil tree lycopods, with which they share some unusual features including the development of both wood and bark, a modified shoot system acting as roots, bipolar growth, and an upright stance.


  • A small, lake-bottom relative of the ferns, with an ancient pedigree.
  • Leaves dark green, grass-like, elongated, up to 30 in number, up to 8" long. Not typical leaves but sporophylls, bearing large micro and megasporangia embedded into the upper leaf surface. At the leaf base is a sac-like sporangium, containing the spores.
  • Stem a two lobe corm with much starch storage, very much reduced in size and no more than the bit of plant between where the leaves attach on top, and the roots on the bottom. Does not elongate, but will grow thicker with age; may even produce small areas of bark.
  • Roots are produced from furrows in the corm. Anatomically quite different from the roots of higher plants, some consider them to be modified leaves rather than typical roots. Thus, they are often referred to as "rooting appendages". This characteristic anatomy of rooting appendages is shared by our Isoetes with the long extinct fossil lycopods.
  • Fruit sporangia, borne within the swollen, paler base of each leaf.
  • Spores white or cream-colored with minute spines (if viewed through microscope); borne May-June.


  • Identifiable as a Quillwort by its small size, multiple spiny basal leaves, and its habitat.
  • Distinguished from the closely related Spiny Spore Quillwort (Isoetes tenella) by its much longer leaves. Lake Quillwort leaves grow to 8" in length while the leaves of Spiny Spore do not exceed 3½".
  • Field Marks
    • always submerged
    • elongated, grass-like leaves in a basal clump



  • This quillwort is almost always found submersed in water.
  • Lakes in the mountains.





  • By spores.



  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Not known to be commercially available.



  • Look for these unusual "ferns" in calm, shallow waters over a sandy bottom.

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Last updated on 26 February, 2004