variable watermilfoil

Haloragales > Haloragaceae > Myriophyllum heterophyllum Michx.
Synonym(s): twoleaf watermilfoil, broadleaf water-milfoil

Variable watermilfoil is a perennial, aquatic herb that has leaves of two noticeably different forms. The submerged leaves are finely dissected, whorled, reddish/greenish-brown, and 1/2-2 1/2 in. (1.3-6.4 cm) long. The emergent leaves are small, oval, bright green, whorled and up to 1/4 in. (0.6 cm) wide. Emergent leaves stand 6-8 in. (15.2-20.3 cm) out of the water and may not be apparent until late summer. Flowering occurs from June to September. Flowers are emergent on 2-12 in. (5.1-30.5 cm), green to reddish stalks. Petals are less than 0.1 in. (3 mm) in length and are subtended by downward curved bracts. Fruits are small, nearly round and have a rough surface. Variable watermilfoil is native to the southern United States, but is considered invasive in much of the northeast. This species is listed as endangered or threatened in three states (Kentucky, Ohio, and Pennsylvania).


Identification, Biology, Control and Management Resources


Selected Images from Invasive.org

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Foliage;
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Infestation;
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Diagram or Graphic; USDA NRCS. Wetland flora: Field office illustrated guide to plant species. USDA Natural Resources Conservation Service.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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Diagram or Graphic; Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 2: 616.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
768x512 / 1536x1024

Invasive Reference(s):

Check Invasive.org for most current lists.
  • Connecticut - Noxious Weed Law
  • Maine - Noxious Weed Law
  • Massachusetts - Noxious Weed Law
  • Rhode Island - Noxious Weed Law
  • Vermont - Noxious Weed Law
  • Invasive Plants of the Upper Midwest
  • Invasive Plant Atlas of New England


External Links


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