alligatorweed

Caryophyllales > Amaranthaceae > Alternanthera philoxeroides (Mart.) Griseb.
Synonym(s): alligator weed, pig weed

Alligatorweed is an emergent or rooted floating plant that invades aquatic areas and adjoining uplands throughout the southern portions of the United States. Plants have hollow stems and can grow to 3 ft. (1 m) tall. Opposite, elliptical leaves are thick but non-succulent and are up to 4 in. (10 cm) long. Flowering occurs during the summer with white, clover-like heads in the axils of the leaves. Alligatorweed roots in wet soils or shallow water and grows out into waterways. Alligatorweed can also grow terrestrially, forming smaller, tougher leaves. The thick mats can displace native vegetation and wildlife habitat, clog waterways, restrict oxygen levels of water, increase sedimentation, interfere with irrigation and prevent drainage. Alligatorweed is native to South America and was first introduced into the United States around 1900 in ballast water.


Identification, Biology, Control and Management Resources


Selected Images from Invasive.org

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Flower(s); the white flowers are arranged in stalked, short, headlike spikes, and have a style
Gary Buckingham, USDA Agricultural Research Service, Bugwood.org
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Flower(s);
Chris Evans, River to River CWMA, Bugwood.org
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Flower(s);
Robert H. Mohlenbrock, USDA NRCS PLANTS Database, Bugwood.org
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Foliage;
Chris Evans, River to River CWMA, Bugwood.org
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Plant(s);
James H. Miller, USDA Forest Service, Bugwood.org
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Plant(s); in flower
Chris Evans, River to River CWMA, Bugwood.org
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Plant(s);
Chris Evans, River to River CWMA, Bugwood.org
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Infestation;
Chris Evans, River to River CWMA, Bugwood.org
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Infestation;
Chris Evans, River to River CWMA, 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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Invasive Reference(s):

Check Invasive.org for most current lists.
  • Alabama - Noxious Weed Law
  • Alabama - IPC List
  • Arizona - Noxious Weed Law
  • Arkansas - Noxious Weed Law
  • California - Noxious Weed Law
  • California - Invasive Plant Inventory
  • Florida - EPPC list
  • Georgia - EPPC list
  • Mississippi - 10 Worst Invasive Weeds
  • South Carolina - Noxious Weed Law
  • Tennessee - EPPC List
  • Texas - Noxious Weed Law
  • Texas - Invasive Plant List
  • Virginia - Invasive Alien Plant Species
  • Mid-Atlantic - EPPC List
  • Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species
  • Invasive Plant Atlas of the Mid-South


External Links


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USDA Forest Service Bugwood University of Georgia