Alligator weed

Alternanthera philoxeroides -- Center for Aquatic and Invasive Plants

Alternanthera philoxeroides

Non-Native to Florida
Origin: South America 1
Introduction to Florida: 1894 (accidental: ballast) 2

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Alternanthera philoxeroides Alternanthera philoxeroides Alternanthera philoxeroides Alternanthera philoxeroides Alternanthera philoxeroides

This species appears on the following legally prohibited plant lists

CATEGORY II on the Florida Exotic Pest Plant Council (FLEPPC) 2011 List of Invasive Plant Species

UF-IFAS Assessment of Non-Native Plants in Florida’s Natural Areas

Download a Recognition Card (PDF 512 KB)

Download a page (PDF) from Identification and Biology of Nonnative Plants in Florida’s Natural Areas – Second Edition1

Alligator weed is an emersed plant. It can grow in a variety of habitats, including dry land, but is usually found in water. It may form sprawling mats over the water or along shorelines.


Sprawling herb, usually in water, often in row crops and gardens. Stems pinkish, can become hollow when larger, to 1 m (3.3 ft) long.


Opposite, narrowly elliptic or spatulate, to 9 cm (3.5 in) long; occasionally a few indistinct teeth on margin.


Reduced, bisexual in round white heads on long stalks from upper leaf axils; each flower with 4–5 thin, papery bracts, 5 stamens, 1 pistil.


Tiny, one-seeded, thin-walled.

Ecological threat

FLEPPC Category II – Invasive exotics that have increased in abundance or frequency but have not yet altered Florida plant communities to the extent shown by Category I species.



Text from Invasive and Non-native Plants You Should Know - Recognition Cards 2

Biological control insects of alligator weed

View the herbarium specimen image from the University of Florida Herbarium Digital Imaging Projects.

For brief control information, see Efficacy of Herbicide Active Ingredients Against Aquatic Weeds by K. Langeland, M. Netherland, and W. Haller.