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Alligator Weed

Alternanthera philoxeroides

Non-Native

Close up Alligator weed flowers
alligator weed drawing

alligator weed on water bank
Alligator weed flower

alligator weed hollow stem

USDA, NRCS. 2018. The PLANTS Database (http://plants.usda.gov, 28 March 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.
Illustration courtesy of University of Florida/IFAS Center for Aquatic and Invasive Plants. Used with permission.

What is Alligator Weed?

Physical Characteristics

Leaves:

  • Opposite
  • Thick and fleshy
  • Smooth
  • Linear to sword-shaped or Oval-shaped and thinner at base
  • 0.78-4.33 inches long
  • 0.2-0.78 inches wide
  • Thin & immobile at base

Flowers:

  • Immobile in the bractlets
  • Sweet scented
  • Smooth
  • 0.2-0.23 inches long
  • Silvery-white
  • Filaments linear/slender

Spikes:

  • Simple
  • Nearly disk-shaped or cylindrical
  • 0.78-2.75 inches long on peduncles

Stem:

  • Simple or branching
  • 1-3.25 inches long
  • Smooth branches
  • Laying along ground, curving upward
  • At or just below the surface of the ground
  • Forming mats
  • Thick

Roots:

  • Rooting at nodes

Where Does it Grow?

EDDMapS. 2024. Early Detection & Distribution Mapping System. The University of Georgia – Center for Invasive Species and Ecosystem Health. Available online at http://www.eddmaps.org/; last accessed January 17, 2024.

Alligator weed is non-native to North America and should not be spread. It is an obligate wetland plant that can be found in waste places in ponds, streams, and along some rivers.

Pros and Cons of Alligator Weed

This is a non-native plant that should not be grown as it is invasive and illegal to possess or transport this species in Texas. Please report sightings to the Texas Parks and Wildlife Department at (512) 389-4800.

How to Manage This Plant
Plant Glossary

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Photo Credits: The majority of the aquatic plant line drawings are the copyright of the University of Florida Center for Aquatic Plants (Gainsville). They are used with permission.

Aquatic plant photographs were provided by David Bayne, Jim Davis, Kelly Duffie, Billy Higginbotham, Michael Masser, John Clayton, Chetta Owens, Diane Smith, Joe Snow, Don Steinbach, Bridget Robinson Lassiter and Peter Woods.

You may use these photos, so long as you give credit to AquaPlant.

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