Hydrilla verticillata

Hydrilla verticillata_Hydrilla_John Madsen_cropped
Photo: John Madsen

Synonyms: Hottonia serrata, Hydrilla angustifolia, Hydrilla dentata, Hydrilla lithuanica, Hydrilla ovalifolia, Hydrilla wightii, Leptanthes verticillatus, Serpicula verticillata, Vallisneria verticillata, Elodea verticillata

Common names: Hydrilla; water thyme; Florida Elodea

Hydrilla verticillata (Hydrilla) is a perennial aquatic plant (family Hydrocharitaceae). It has been observed in the Mojave and Colorado deserts, south and central coasts, San Francisco Bay Area, and Central Valley. Currently, isolated infestations of Hydrilla are found in Shasta, Yuba, Lake, Calaveras, Madera, Mariposa, and Imperial counties. Hydrilla forms large mats that fill the water column and can block or severely restrict water flow.

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.

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 Hydrilla verticillata 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.
  • 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

    Hydrilla verticillata_leaves with saw-tooth edge_copyright2001_DeanKelch(CDFA)
    Hydrilla verticillata (Hydrilla) leaves with saw-tooth edge. Photo: &#169 2001 Dean Kelch, CDFA
    Hydrilla verticillata_leaves, stems, and reproductive buds_copyright2001_DeanKelch(CDFA)
    Hydrilla verticillata (Hydrilla) leaves, stems, and reproductive buds. Photo: &#169 2001 Dean Kelch, CDFA
    Hydrilla verticillata_whole plant with tuber_copyright2001_FredHrusa(CDFA)
    Hydrilla verticillata (Hydrilla) whole plant with tuber. Photo: &#169 2001 Fred Hrusa, CDFA
    Hydrilla verticillata_infestation_copyright2001_FredHrusa(CDFA)
    Hydrilla verticillata (Hydrilla) infestation. Photo: &#169 2001 Fred Hrusa, CDFA