Hypericum perforatum (Common St. Johnswort)

Plant Info
Also known as: Klamath-weed
Genus:Hypericum
Family:Hypericaceae (St. John's-wort)
Life cycle:perennial
Origin:Europe
Status:
  • Invasive - ERADICATE!
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):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 5-petals Cluster type: flat

[photo of flower]  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: Leaf attachment: opposite Leaf type: simple

[photo of leaves] 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.

Fruit: Fruit type: capsule/pod

[photo of fruit] Seed pod is a 3-sectioned capsule, about ¼ inch long, that turns deep reddish brown as it matures. Each section has a little “tail” at the top.

Notes:

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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More photos

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.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Mark - Oakdale Nature Preserve, Oakdale MN
on: 2010-06-19 16:53:05

June 2010, in the meadow southwest of the Discovery Center.

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