Common St John's-wort (Hypericum perfoatum)

 
 
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Poisonous

Description
Erect perennial that grows to 1.2 m tall, with rhizomes. Reddish stems are single or multiple, smooth, somewhat two-edged, woody at the base, and branching out toward the top of the plant. Leaves opposite, elliptic-oblong to linear, 1-3 cm long, stalkless, flat, hairless, green, 3- to 5-veined from the base, dotted with numerous, tiny translucent glands that are visible when a leaf is held up to the light. Edges of leaf lower surfaces lined with elevated black glands. Bright yellow flowers, ~ 2 cm in diameter, clustered at the stem tips. Petals 5, separate, 8-12 mm long, typically dotted with black glands along the margins. Plants typically do not flower the first year. Capsules 3-chambered, ovate, not lobed, sticky-glandular, 5-10 mm long, with persistent styles 3-10 mm long, open longitudinally to release seed. Seed shiny black to brown, nearly cylindrical, ~ 1 mm long, densely pitted, often coated with gelatinous material from the capsule that aids dispersal and may inhibit germination until it breaks down or leaches out in about 4-6 months.
Foliage contains hypericin, a fluorescent
red pigment that is toxic to livestock when consumed in quantity, especially to animals with light-colored skin. Used in herbal medicine, hypericin is the antidepressant ingredient in St. Johns-wort remedies.

Key Identifiers
  • Opposite elliptic-oblong to linear leaves, 3-5 veins, dotted with numerous translucent and black glands
  • Bright yellow flowers, typically dotted with black glands along margins
Location in Canada
Due to its popularity in the medicinal industry we suspect ornamental plants to exist in Alberta.

Resources
USDA National Invasive Species Information Centre - St John's wort
California Department of Food and Agriculture - St John's wort

Similar species
Hypericum spp. – According to Flora of Alberta two other species in Hypericum have been known to exist in Alberta. H. formosum has ovate-oblong to suborbicular, black-dotted along the margin leaves. H. majus has lancelolate, not black dotted leaves.

Richard Old, XID Services, Inc., Bugwood.org

Norman E. Rees, USDA Agricultural Research Service- Retired, Bugwood.org

 
 
 
 

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For more information about the content of this document, contact Nicole Kimmel.
This document is maintained by Shelley Barkley.
This information published to the web on April 10, 2012.
Last Reviewed/Revised on March 21, 2014.