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

Video ID segment (2-3 minutes / transcript below)
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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

See Table 1 in Florida's Established Arthropod Weed Biological Control Agents and Their Targets (2013) for a list of arthropod biological control agents that occur on this species.

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

Video Transcript

Alligator weed - Alternanthera philoxeroides
Alligator weed is not native to Florida.

Alligator weed can grow in a variety of habitats, although it is usually found in water. Sometimes it forms sprawling mats over deep rivers, or along shorelines. Sometimes it is a pest on land. Alligator weed is an herb that occurs throughout Florida and flowers in the warm months. It has smooth stems that trail along the ground or out across the water. The stems are hollow. They have nodes from which other stems and roots grow. The simple leaves of alligator weed are elliptic and have smooth margins. The leaves are opposite, which means that two leaves grow on opposite sides of the stem, at the same place on the stem. The distinctive white flowers can be easily recognized. What appears to be one flower is actually a cluster of several flowers. They are whitish and papery looking and feeling. The flower cluster grows on a stalk that can be 2 inches long.

    Alligator weed has
  • whitish, papery flowers on stalks,
  • sprawling stems that are hollow, and
  • leaves that are opposite on the stem.

Biological control insects of alligator weed

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