alligatorweed: Alternanthera philoxeroides (Caryophyllales: Amaranthaceae): Invasive Plant Atlas of the United States

alligatorweed	USDA PLANTS Symbol: ALPH U.S. Nativity: Exotic Habit: Aquatic Plants Forbs/Herbs
Alternanthera philoxeroides (Mart.) Griseb.

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Taxonomic Rank: Magnoliopsida: Caryophyllales: Amaranthaceae
Synonym(s): alligator weed, pig weed
Native Range: So. Amer. (GRIN);
Appearance Alternanthera philoxeroides 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. Foliage Opposite, elliptical leaves are thick but non-succulent and are up to 4 in. (10 cm) long. Flowers Flowering occurs during the summer with white, clover-like heads in the axils of the leaves. Fruit Fruits are very small, and single-seeded. Ecological Threat Alternanthera philoxeroides roots in wet soils or shallow water and grows out into waterways. Alternanthera philoxeroides 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. It is native to South America and was first introduced into the United States around 1900 in ballast water.

Identification, Biology, Control and Management Resources

Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
Invasive Alien Plant Species of Virginia - Virginia DCR and Virginia Native Plant Society
Global Invasive Species Database - Invasive Species Specialist Group
Images, Video and Information - University of Florida - Center for Aquatic and Invasive Plants

Selected Images from Invasive.org

View All Images at Invasive.org

Flower(s); Chris Evans, University of Illinois, 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, University of Illinois, Bugwood.org Additional Resolutions & Image Usage	Plant(s); in flower Chris Evans, University of Illinois, 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, University of Illinois, Bugwood.org Additional Resolutions & Image Usage
Infestation; Chris Evans, University of Illinois, 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 NRCS 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