Online Virtual Flora of Wisconsin - Hypericum perforatum

Hypericum perforatum L.

Family: Hypericaceae

common St. John's-wort, Klamath-weed, St. John's-wort

Christopher Noll

Merel R. Black

University of Wisconsin - Madison (WIS-VP)

Open Interactive Map

Etymology: Hypericum: ancient Greek name derived from hyper, "above," and eikon, "picture," from old practice of placing flowers above an image in the house to ward off evil spirits at the midsummer festival of Walpurgisnacht, which later became feast of St. John
Plants: erect, perennial, 2'-3' tall forb with many leafy branches; stems with a sharp ridge below the base of the leaves
Leaves: stalkless, small, 1/4" wide leaf drawing

Flowers: yellow, 5-parted, 5/8"-1" wide, stalked, petals with black dots near the edges; inflorescence a many-flowered, rounded to flat, compound, branched cluster (cyme); blooms June-Sept.
Fruits: 3 chambered capsule fruit drawing

Habitat: disturbed sites, fields, roadsides
Hazardous: Careful, this plant is hazardous!
Invasiveness: Invasive - Eradicate!
Conservation Status: Introduced - naturalized; ecologically invasive

Fields, thickets, along roadsides and railroads, dry to mesic prairies, dumps, old quarries, oak barrens, along trails and logging roads, beaches and lake dunes, sand and gravel pits, clay bluffs, rock outcrops, blufftops, lakeshores, thin woods of oak or pine, open sandy areas. Our only species introduced from Europe, first collected in 1860. Contact of the sap with exposed skin can cause photodermatitis in some people.