Skip to main content

Common St. Johnswort (Hypericum perforatum)

Common St. Johnswort Common Names: St. John's wort, Klamathweed

Description: Grow in dense patches; plants have been used to treat mild depression, but have been shown to cause hyper photosensitivity.

Habit: Perennial, rhizomatous herb that can reach 1.2 m (4 ft) in height; long taproot with shallow, slender, branched root system.

Leaves: Opposite, sessile, elliptic, 2/5- 1 1/5 in. (1-3 cm) long, dotted with many pellucid glands.

Stems: Erect with numerous branches and up to 3 ft tall; often reddish in color and become woody at the base with maturity.

Flowers: Bright yellow flowers develop at the tips of the stems, flowers have five petals and many stamens, 5/8-1 in wide, petals typically have black glands along the margins.

Fruit and seeds: Fruits are three-chambered capsules with three persistent styles, contains numerous dark brown to black cylinder-shaped seeds.

Habitat: Native to Europe. Found in disturbed sites, rangelands, pastures, roadsides and forest clearings.

Reproduction: By seeds and short runners.

Similar species: Spotted St. Johnswort (Hypericum punctatum), which has black dots and streaks along the interior of the flower petals while others lake black dots.

Monitoring and rapid response: Hard to control. Physical and Chemical controls have been ineffective due to extensive root system and wax on its leaves.

Credits: The information provided in this factsheet was gathered from the Invasive Plant Atlas and the USDA PLANTS database.

Individual species images that appear with a number in a black box are courtesy of the network ( photo author credits may not be included due to the small display size of the images and subsequent difficulty of reading the provided text. All other images appear courtesy of Google (

Common Name:

Common St. Johnswort

Scientific Name:

Hypericum perforatum







USDA Symbol: