common St. Johnswort

Theales > Clusiaceae > Hypericum perforatum L.
Synonym(s): Klamathweed, St. John's wort

Common St. Johnswort is a perennial, rhizomatous herb that can reach 4 ft (1.2 m) in height. Leaves are opposite, sessile, elliptic, 2/5- 1 1/5 in. (1-3 cm) long and dotted with many pellucid glands. Flowering occurs from June to September, when bright yellow flowers develop at the tips of the stems. Flowers have five petals and many stamens. Petals typically have black glands along the margins. Fruits are three-chambered capsules with three persistent styles. Plants have been used to treat mild depression, but have been shown to cause hyper photosensitivity. St. Johnswort is native to Europe and may be poisonous to cattle in large doses. Plants inhabit rangelands, pastures, roadsides and forest clearings.


Identification, Biology, Control and Management Resources


Selected Images from Invasive.org

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Plant(s);
Richard Old, XID Services, Inc., Bugwood.org
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Feature(s); pellucid dots on leaves
Richard Old, XID Services, Inc., Bugwood.org
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Flower(s);
Richard Old, XID Services, Inc., Bugwood.org
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Flower(s);
Norman E. Rees, USDA Agricultural Research Service, Bugwood.org
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Flower(s);
David Cappaert, Michigan State University, Bugwood.org
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Flower(s);
Steve Dewey, Utah State University, Bugwood.org
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Flower(s);
Jamie Nielsen, University of Alaska Fairbanks, Cooperative Extension Service, Bugwood.org
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Flower(s);
Steve Dewey, Utah State University, Bugwood.org
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Feature(s); Roots
Steve Dewey, Utah State University, Bugwood.org
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Fruit(s);
Steve Dewey, Utah State University, Bugwood.org
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Plant(s); Mature plant
Norman E. Rees, USDA Agricultural Research Service, Bugwood.org
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Plant(s); St. John's Wort, native to Eurasia, is a serious problem in parts of the West where it displaces native plants that are important in maintaining soil nutrients, microbial activity, and water cycling.
Carol DiSalvo, USDI National Park Service, Bugwood.org
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Infestation; research site near
Norman E. Rees, USDA Agricultural Research Service, Bugwood.org
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Seed(s);
Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org
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Diagram or Graphic; Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 2: 533.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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Invasive Reference(s):

Check Invasive.org for most current lists.
  • California - Noxious Weed Law
  • California - Invasive Plant Inventory
  • Colorado - Noxious Weed Law
  • Kentucky - EPPC List
  • Montana - Noxious Weed Law
  • Nevada - Noxious Weed Law
  • Oregon - Noxious Weed Law
  • South Dakota - Noxious Weed Law
  • Washington - Noxious Weed Law
  • Wyonming - Noxious Weed Law
  • Invasive Plants: Western North America
  • Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species
  • Invasive Plants of the Upper Midwest


External Links


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