| alligatorweed | USDA PLANTS Symbol: ALPH U.S. Nativity: Exotic Habit: Aquatic Forbs/Herbs |
| Alternanthera philoxeroides (Mart.) Griseb. |
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Taxonomic Rank: Magnoliopsida: Caryophyllales: Amaranthaceae |
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| Synonym(s): alligator weed, pig weed | |
| Native Range: So. Amer. (GRIN); | |
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. |
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Identification, Biology, Control and Management Resources
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| Selected Images from Invasive.org | View All Images at Invasive.org |
 Flower(s); Robert H. Mohlenbrock, USDA NRCS PLANTS Database, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); the white flowers are arranged in stalked, short, headlike spikes, and have a style Gary Buckingham, USDA Agricultural Research Service, Bugwood.org Additional Resolutions & Image Usage |
 Foliage; Opposite leaves Rebekah D. Wallace, University of Georgia, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Foliage; Chris Evans, Illinois Wildlife Action Plan, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); in flower Chris Evans, Illinois Wildlife Action Plan, Bugwood.org Additional Resolutions & Image Usage |
 Fruit(s); Fruit with attached perianth. Similar to an FNW taxon. Julia Scher, USDA APHIS PPQ, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; Chris Evans, Illinois Wildlife Action Plan, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; Chris Evans, Illinois Wildlife Action Plan, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); 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 Additional Resolutions & Image Usage |
| EDDMapS Distribution: This map is incomplete and is based only on current site and county level reports made by experts and records obtained from USDA Plants Database. For more information, visit www.eddmaps.org Alternative content
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 State(s) Where Reported invasive. Based on state level agency and organization lists of invasive plants from WeedUS database. Alternative content
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| U.S. National Parks where reported invasive: |
| Colonial National Historical Park (Virginia) |
