Hypericum perforatum (Common St. Johnswort)
|Also known as:||Klamath-weed|
|Family:||Hypericaceae (St. John's-wort)|
|Habitat:||sun; fields, roadsides, woodland edges, disturbed soil|
|Bloom season:||June - September|
|Plant height:||1 to 3 feet|
|Wetland Indicator Status:||GP: UPL MW: FACU NCNE: UPL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Flowers are about 1 inch across, 5 yellow petals with tiny black dots around the edges, and numerous long yellow-tipped stamens, which may also be dotted, exploding from the center. Each flower is usually on a short stalk, with many flowers branching off the top part of the plant.
Leaves and stems:
Leaves are generally oval to oblong, 1 to 2 inches long, about ¼ inch wide, with rounded tips and no leaf stalk, oppositely attached. Most leaves have scattered tiny translucent dots; when held up to the light they give the impression the leaf is perforated (and is where the scientific name comes from). Stems are green, smooth and leafy.
The dots on the leaves and petals are actually sacs of essential oils, used as an herbal remedy to treat everything from depression to infection. The black dots on the petals can dye your skin red when they're crushed. Common St. John's-wort can be quite invasive, forming dense colonies and crowding out native plants. Roadside infestations have become a common sight. In Ownbey and Morley's plant atlas Vascular Plants of Minnesota, published in 1991, there were only a dozen records in 8 counties. In 20 years this has jumped to 57 records in 24 counties and I have no doubt it is still an under-reported species. All Hypericum species have switched from the Clusiaceae family to Hypericaceae.
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- Common St. John's-wort plant
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- a roadside infestation
- a colony of Common St. Johnswort
Photos by K. Chayka taken at Long Lake Regional Park, Ramsey County. Photos courtesy Peter M. Dziuk taken in Anoka County, and along a highway ramp in St. Paul.
Have you seen this plant in Minnesota, or have any other comments about it?