common St. Johnswort
Family
HypericaceaeScientific Name
Hypericum perforatumOther Common Names:
klamathweed
St. johnswort
klamath weed
goatweed
perforate St. john s-wort
tipton weed
rosin-rose
Habit
Herb
Leaves
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.
Identifying Characteristics
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.
Seed Fruit
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.
Where Found
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.
Growth Habit
woody bush or tree
Thorns or Spines
not present
Approximate Flower Diameter
Varies:
dime,
nickle,
quarter
Dominant Flower Color
yellow
Flower Symmetry
radial symmetery
Leaf Hairs
no hairs
Leaf Shape
oval
Leaf Arrangement
opposite
Leaf Margin
entire
Leaf Structure
simple
Leaf Stalk
none
Stem Hairs
no hairs
Stem Cross Section
round or oval
Milky Sap
not present
Root Structure
Varies:
taproot,
rhizomes present,
stolons present
Life Cycle
perennial
Ochrea
not present
Plant Type
Herb