Lobelia dortmanna

Water Lobelia

Water Lobelia, Photo courtesy of Wisconsin State Herbarium and Kitty Kohout
Water Lobelia
Photo courtesy Wisconsin State Herbarium and Kitty Kohout

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


  • Lobelia, named after the botanist Matthias de Lobel, a native of Lille, who died in London in 1616
  • dortmanna, from the Latin, "Dortmann's"
  • Water Lobelia, from its habit, unusual for Lobelia, as an emergent aquatic plant.
  • Other common names include: Dortmann's Cardinalflower, Tvepibet Lobelie (Dan), Nuottaruoho (Fin), Flùr an Lochain (Gaelic), Wasser-Lobelie (Ger), Botnegras (Nor), Notblomster, Notgräs (Swe)
  • , Lobelia jeziorna (Pol)


  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Asteridae
        • Order Campanulale
          • Family Campanulaceae, the
            • Genus Lobelia, the Lobelias
  • Taxonomic Serial Number: 34516


  • A hardy lakeshore perennial of shallow water.
  • Leaves simple, alternate, linear, fleshy, hollow; 1"-3" long with blunt tip, in dense rosettes at base of plant. Short stiff leaves lack stomata and are covered by a thick cuticle providing high resistance to gas exchange and water loss. The thick cuticle and lack of stomata maintain high CO2 concentrations (over 20 times air levels) for photosynthesis within the leaf lacunae. Stem leaves tiny.
  • Stem erect, hollow, smooth; with milky sap
  • Roots white, forming large clumps. Able to take up virtually all its carbon dioxide (CO2) needs from the CO2-rich bottom sediments (roughly 30 times air level) and release a substantial proportion of the oxygen (O2) produced during photosynthesis. This leads to O2 concentrations close to saturation in the root zone and O2 penetration to great sediment depth because of low microbial O2 consumption rates in these waters. The release of O2 from the roots helps to ensure efficient aerobic degradation of organic matter, leads to oxidized forms of Fe, Mn, and N, and can supply O2 to mycorrhiza fungi and aerobic fauna associated with the roots.
  • Flowers pale blue to white, perfect, irregular; ¼"-¾" long, in a few flowered raceme.
    • Sepals 5, 2mm long
    • Petals 5, fused into a 2 lobe upper lip and 3 lobe lower lip.
    • Stamens 5, joined to form a tube around the style
    • Ovary superior (within blossom)
  • Fruit a many seeded capsule
  • Seed


  • A small plant, growing on the sandy bottoms of acidic, nutrient poor northern lakes.
  • Distinguished from similar plants by:
    • rosette of thick, linear, hollow leaves
    • tubular white flowers blooming above the water's surface


  • Newfoundland to Minnesota, south to New Jersey; also the Pacific coast.
  • Europe.


  • Shallow waters of acid lakes and ponds; grows in sandy sediments of nutrient-poor lakes and may become exposed to the air during summer months.
  • Adapted to growing in acidic softwater lakes that have extremely low levels of Dissolved Inorganic Carbon in the water and so absorbs CO2 from the sediment through their roots.




  • A tincture of the fresh plant has been used to cure headaches and noises in the ears.


  • Reproduces by seed and vegetatively by rhizomes
  • Flowers July-September; deep water plants do not flower.


  • By rhizome division


  • Hardy to USDA Zone 3 (average minimum annual temperature -40ºF)
  • Not generally available for the home water garden.



  • Look for this unusual northern plant growing on the sandy bottom at shallow portage landings in the BWCA.

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Last updated on 3 July, 2004