Hypericum perforatum

Hypericum perforatum_common St. Johnswort_flower_JM DiTomaso
Lake Tahoe Basin Weed Coordinating Group

Common names: St. John's wort; klamathweed; tipton weed; goatweed

Hypericum perforatum (common St. Johnswort, klamathweed) is an perennial plant (family Clusiaceae) grown for medicinal use, but it can be toxic to light colored livestock when consumed in large quantities. By 1940, more than 1 million hectares of California were infested by St. Johnswort, but biological control agents have eliminated most populations below 1500 m elevation.

Cal-IPC Rating: Limited

Cal-IPC Assessment

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 RIC 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.

There are no Symposium presentations associated with this species yet.

Other Hypericum perforatum Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - See the distribution of this species on Calflora's map of California.
  • CalWeedMapper - Distribution information with ability to determine regional priorities.
  • Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • CDFA - California official noxious weeds.
  • USDA PLANTS Database - Federal database with information on identification and distribution, and links to websites in individual states.