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Montana Field Guide

Montana Field Guides

Common St. John's-wort - Hypericum perforatum
Other Names:  Klamath Weed, Common St. Johnswort

Noxious Weed: Priority 2B
Non-native Species

Global Rank: GNR
State Rank: SNA

Agency Status
MNPS Threat Rank:
C-value: 0

External Links

General Description
Taprooted and rhizomatous. Stems 25–75 cm tall. Leaves lanceolate, 1–3 cm long, black-dotted on the margins. Flowers: sepals linear-lanceolate, 5–8 mm long; petals 8–14 mm long with black-dotted margins. Capsule 5–8 mm long with brown seeds (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Species Range

Range Comments
Introduced throughout much of temperate North America; native to Europe (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 12098

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Grassland, open forest, pastures, roadsides; valleys, montane (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).


  • Additional ReferencesLegend:   View Online Publication
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    • Lesica, P., M. T. Lavin, and P. F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Morris, M. S., and J. Meuchel. 1956. The problem of St. Johnswort: a noxious plant in western Montana. Montana For. And Cons. Exp. Sta., School of For., University of Montana, Missoula. Bull. No.4. 8 pp.
    • Nelson, H.S. 1955. The phenology of goatweed, Hypericum perforatum in relation to the behavior of goatweed beetles, Chrysolina gemellata and C. hyperici, in western Montana. M.S. thesis. Montana State University, Missoula. 45 pp.
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Citation for data on this website:
Common St. John's-wort — Hypericum perforatum.  Montana Field Guide.  .  Retrieved on , from