Hypericum perforatum (St. John's wort, klamathweed)

Hypericum perforatum

Lake Tahoe Basin Weed Coordinating Group

Hypericum perforatum (common St. Johnswort, klamathweed) is an annual herb/forb (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 Inventory rating: Moderate

Cal-IPC Resources on Hypericum perforatum

• California Invasive Plant Inventory Assessment Form (pdf) - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.
• Cal-IPC News - Articles from our quarterly newsletter. Each issue is available as a pdf. List of articles on Hypericum perforatum.
• Cal-IPC Symposium Proceedings - Presentations and papers from our annual Symposium. List of articles on Hypericum perforatum.

Cal-IPC News Articles

• (1995). Biological control of invasive exotic pest plant species: A report on the importance of maintaining and enhancing our nation's biological control capabilities. CalEPPC News. 3: 6-10.
• Connick, S. and M. Gerel (2005). Don't sell a pest: A new partnership to prevent plant invasions through horticulture. Cal-IPC News. 13: 4-5,14.
• Donaldson, S. (2003). Fighting weeds in the Tahoe basin. CalEPPC News. 11: 7.
• Hoekstra, B. (1997). Klamathweed. CalEPPC News. 5: 9.
• Pitcairn, M. (2000). All weeds that have approved biological control agents, accidental introductions and others. CalEPPC News. 8.

Cal-IPC Symposium Proceedings

• Connick, S. and M. Gerel (2004). Partnering to prevent invasions of plants of horticultural origin. California Invasive Plant Council Symposium 2004. Ventura, CA.
• Donaldson, S., W. West, et al. (2003). Getting the job done: Working within the regulatory environment at Lake Tahoe to manage weeds. California Invasive Plant Council Symposium 2003. Kings Beach, CA.
• Kirk, A. A., T. Widmer, et al. (2003). The potential contribution of natural enemies from Mediterranean Europe to the management of the invasive weed Arundo donax (Graminae; Arundinae) in the U.S. California Invasive Plant Council Symposium 2003. Kings Beach, CA.
• Pitcairn, M. J. and D. M. Woods (1998). Control methods: Biological control. California Exotic Pest Plant Council Symposium '98. Ontario, CA.
• Pitcairn, M. J. and D. M. Woods (1998). Control methods: biological control. California Exotic Pest Plant Council Symposium 1998. Ontario, CA.
• Thomsen, C. D., W. A. Williams, et al. (1996). Yellow starthistle management with grazing, mowing, and competitive plantings. California Exotic Pest Plant Council Symposium '96. San Diego, CA.

Other Resources on Hypericum perforatum

• USDA PLANTS database - Federal database with information on identification and distribution, and links to websites in individual states.
• Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from the UC Berkeley Jepson Herbarium.
• CalFlora - Distribution information by county based on submitted observations and herbarium specimens.
• The Nature Conservancy Management Summary - Information compiled by TNC land managers. Photos included for some species.
• CalPhotos - Images of plants taken mostly in California.

Printer-friendly version