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Taxon  Report  
Hypericum perforatum  L.
Common st. johnswort,   Klamath weed,   Klamathweed
Hypericum perforatum is a perennial herb that is not native to California.
Cal-IPC rating: moderate
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Observation Search
~4842 records in California
redone or more occurrences
within a 7.5-minute quadrangle
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Bloom Period
Subspecies and Varieties:
Genus: Hypericum
Family: Hypericaceae  
(Clusiaceae)
Category: angiosperm  
PLANTS group:Dicot
Jepson eFlora section: eudicot

Toxicity: Possible skin irritation from touching any part of this plant.

Wetlands: Occurs usually in non wetlands, occasionally in wetlands

Habitat: disturbed, disturbed

Communities: weed, characteristic of disturbed places

Name Status:
Accepted by PLANTS

Information about  Hypericum perforatum from other sources
USDA PLANTS Profile (HYPE)

Photos on Calflora

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Google Images

Photos on iNaturalist

[Wikipedia] Eurasia native: Possibly a hybrid between H. maculatum and H. attenuatum, the species can be found across temperate areas of Eurasia and has been introduced as an invasive weed to much of North and South America, as well as South Africa and Australia. While the species is harmful to livestock and can interfere with prescription drugs, it has been used in folk medicine over centuries, and remains commercially cultivated in the 21st century. (contributed by Mary Ann Machi)

[Cal-IPC] Invasive: Hypericum perforatum (common St. Johnswort, klamathweed) is a 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. (contributed by Mary Ann Machi)


Suggested Citation
Calflora: Information on California plants for education, research and conservation, with data contributed by public and private institutions and individuals. [web application]. 2024. Berkeley, California: The Calflora Database [a non-profit organization]. Available: https://www.calflora.org/   (Accessed: 04/12/2024).