St.Johns Wort (Hypericum perforatum)

St. John’s Wort

Hypericum perforatum

Description

  • St. John’s Wort (Hypericum perforatum) is a perennial plant which can grow up to 1m tall.
  • The flowers are bright yellow with five petals, appearing in clusters of up to 100 flowers per stem. The leaves are small and ellipse shaped.
  • When held up to the sun, the leaves appear “perforated,” having many small, translucent dots.
  • After flowering, capsules form containing many seeds, which can remain viable in the soil for up to ten years.
Leaves appear perforated when held up to light

Consequences of invasion

  • St. John’s Wort contains two toxins, hypericin and hypericum red which can cause photosensitivity, weight loss or (rarely) death, if consumed in large quantities by grazing animals.
  • The rapid and dense spread of this plant reduces the growth of native species, consequently decreasing amount of appropriate food available for livestock and wildlife.

Introduction and spread

  • The plant is native to Europe, western Asia and North Africa.
  • As it is used in herbal medicine, it has likely been spread and cultivated for this purpose.
  • The plant reproduces by both seed and vegetative reproduction.
  • The seeds are easily dispersed by wind, water, animals or human activity and can grow asexually without pollination (apomixes).
  • The roots spread laterally and new plants can sprout from these roots, forming an interconnected system of plants.

Management

  • Prevention is the most effective option – this plant should not be cultivated for any purpose.
  • Select non-invasive plants for your garden, become PlantWise.
  • Removing only the stems stimulates regrowth as the root system is difficult to remove.
  • Tilling the soil and then immediately replanting with other perennial grasses may be effective.
  • Two biocontrol beetles have been released in BC (Chrysolina spp.) with some success.
  • Other biocontrol agents are still being researched.
  • Chemical control may be an option in certain situations, contact a local professional to determine whether this will be appropriate.
Chrysolina quadrigemina biocontrol beetle

More Information Available

ISCBC Fact Sheet
Alberta Invasive Species Council Fact Sheet
Cornell University Biological Control

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