Alternanthera philoxeroides

Alternanthera philoxeroides_alligatorweed_JM DiTomaso
Photo: Joseph DiTomaso

Synonyms: Bucholzia philoxeroides Mart., Telanthera philoxeroides (Mart.)

Common names: alligatorweed

Alternanthera philoxeroides (alligatorweed) is a noxious herbaceous aquatic perennial (family Amaranthaceae), that forms dense floating mats. This weed grows in the San Joaquin Valley (Tulare and Kings counties), Los Angeles County, and the Sacramento Delta. It invades lakes, streams, canals, ponds and irrigation ditches. It was previously used in the aquarium trade and is currently rapidly expanding in waterways across California.

Cal-IPC Rating: High?

CDFA Rating: A*?


Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.

Special Reports

Yolo County Weed Alert by Brenda Grewell, April 2020

Weed Management Notes

  • Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

Other Alternanthera philoxeroides Information

  • Bugwood - National database from the Center for Invasive Species and Ecosystem Health at the University of Georgia.
  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - Distribution map and records of this species in California.
  • CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
  • EDDMapS - Distribution of this species in North America.
  • GBIF - Global distribution information.
  • Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.
  • Additional photos

    Alternanthera philoxeroides_stem, leaves, and inflorescence_copyright2001_CDFA(DeanKelch)
    Alternanthera philoxeroides (alligatorweed) stem, leaves, and inflorescence. Photo: &#169 2001 Dean Kelch, CDFA
    Alternanthera philoxeroides_adventitious roots from stem_copyright2001_CDFA(FredHrusa)
    Alternanthera philoxeroides (alligatorweed) adventitious roots from stem. Photo: &#169 2001 Fred Hrusa, CDFA
    Alternanthera philoxeroides_growth habit_copyright2001_CDFA
    Alternanthera philoxeroides (alligatorweed) growth habit. Photo: &#169 2001 CDFA