common St. Johnswort
Scientific NameHypericum perforatum
Other Common Names:
klamathweed St. johnswort klamath weed goatweed perforate St. john s-wort tipton weed rosin-rose
The ~1-2 in (25mm-50mm) long and 3/8 in (9mm) wide. The leaves are entire, oblong/linear, have rounded tips, hairless, and are arranged opposite each other without a petiole. There are yellow/green translucent patches/dots on the leaves.
Common St. Johnswort is a perennial forb with many stems that is typically 1-3 ft tall. It spreads through seeds and runners, both above and below ground. The stems have rusty coloration and are woody at the base. While it is considered a weed, it is also poisonous. Light skinned animals are typically the most affected by this photosensitizing reaction. After an animal eats the plant, it may blister on the skin and lose hair. The best treatment is to get the animals out of the sunlight. It has a deep taproot that helps in times of dry weather.
Flower Seed Head
The flowers are regular, symmetrical around the center point, and arranged in a flattop group. There can be many flowers on each stem. Each flower has ~5 yellow/orange petals and sepals and their small black dots may be seen on the margins. The average flower is a little less than an inch (25mm) across.
Each plant may produce 15-23,000 seeds (due to its high number of flowers). The sticky seed pod is a 3-sectioned capsule that turns deep reddish brown as it matures. The small (1 mm), round, darkly colored seeds have a resinous smell like turpentine. The sticky outer coat on the seeds helps it spread by sticking to animals and clothing.
St. Johnswort can be found in pastures, meadows, and forests. It grows in well-drained areas because it does not grow in wet conditions, but likes coarse-textured soils.
woody bush or tree
Thorns or Spines
Approximate Flower Diameter
Dominant Flower Color
Stem Cross Section
round or oval