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Common St. John's wort
Photo Credit: Daniel Laubhann

Common Name: Common St. John's wort

Scientific Name: Hypericum perforatum

Habitat: disturbed areas, roadsides, grassland

Provincial Designation: Prohibited Noxious

Prohibited Noxious weeds are plant species that are designated as "prohibited noxious" in the Alberta weed regulation. Prohibited noxious weeds must be destroyed, meaning all growing parts need to be killed or the plant's reproductive mechanisms need to be rendered non-viable.


Common St. John’s wort is a perennial herb native to Europe, western Asia, and North Africa. It was introduced to North America in 1696 as a medicinal plant and has been used to treat depression.

Legislated Because

Common St. John’s wort invades rangeland where it can form dense colonies. It contains two toxic compounds which can cause photosensitivity in grazers. If consumed in sufficient quantities it can lead to weight loss and even death.


The yellow flowers are about 2 cm wide. Each of the five petals have small black dots along the petal’s edge.

The leaves are only up to 3 cm long, egg-shaped or elliptic, and are oppositely arranged along the stem.

Unique, translucent dots on the leaf surface make the leaf look perforated when held up to the light.

The plant grows up to 90 cm tall.

Learn more about this species:

See Fact Sheet - Alberta Invasive Species Council

For More Information

Weed Identification


In Edmonton: 311

Outside Edmonton: 780-442-5311


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