Hypericum perforatum

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St. John's Wort or Klamath weed

Hypericum perforatum L.
  • Present in Alberta – Yes
  • Global Invasive Species Database –
  • NatureServe Rank – High/Medium concern. Prolific reproductive ability. Treat infestations early.
  • Haber, Upland –
  • Haber, Wetland –
  • CWF, Status & Invasive Range –
  • Alberta Revegetation Guidelines –
  • The Nature Conservancy –
  • CBCN –
  • AB Weed – Prohibited Noxious


Has been known in Waterton Lakes National Park since 1996. It is confined to date (2007 report) to low elevation, disturbed sites, along roads. This is a different habitat and range from the native species, H. formosum var. scouleri, which typically is in moist, subalpine meadows, also primarily in the Waterton area. From photographs of flowers alone, it would be possible to mistake one for the other.

In 2013, a single specimen was found approx 13 km SW of Dorothy, AB.

Hypericum perforatum L. - common St.Johns wort USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 2: 533.