Common St. Johnswort (Hypericum perforatum): yellow Minnesota wildflowers

Common St. Johnswort

Plant Info
Also known as:	St. John's Wort
Scientific name:	Hypericum perforatum
Family:	St. Johnswort (Clusiaceae)
Life cycle:	perennial
Origin:	Europe
Habitat:	sun; fields, along roads
Bloom season:	summer, fall
Plant height:	1 to 3 feet
USDA PLANTS database:	Minnesota county distribution map
Spotted in Ramsey County at:	Long Lake Regional Park Rice Creek Trail Corridor Vadnais/Snail Lake Regional Park

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Flower:: Flowers are about 1 inch across, 5 yellow petals with tiny black dots around the edges, and numerous long yellow-tipped stamen exploding from the center. Each flower is usually on a short stem, with many flowers branching off the top part of the plant.
Leaves:: Leaves are generally oval to elliptical, 1 to 2 inches long, about ¼ inch wide, with rounded tips and no leaf stem, oppositely attached on many branches. Most leaves have scattered tiny transluscent dots; when held up to the light they give the impression the leaf is perforated (and is where the scientific name comes from).
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:: Common St. Johnswort can be invasive, forming dense colonies and crowding out native plants. 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.

More yellow wildflowers. Photos taken at Long Lake Regional Park, New Brighton, MN July 2006 and June-July 2007

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