Common St. Johnswort
Discuss this plant with the guide — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.
Hypericum perforatum
Colorado noxious weed · List C — Manage widespread weeds. CO-rules-2025
Widespread and well established. Control is recommended by the state; local governments may require management. This is a management category, separate from danger ratings. Category source · What the lists mean.
Photosensitivity and animal exposure concerns. Exposure help.
Still researching this plant
This is a sourced working profile. Evidence is incomplete for Dogs & cats. Independent botanical and veterinary review is pending. Uncertainty is not a finding that the plant is safe.
Three views of this plant
Source-identified reference photographs; these are not a complete identification key. A source location outside Colorado does not establish local occurrence.
W. Bulach · CC BY-SA 4.0
Photo source and identification
Original record · Original image
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Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
Sten Porse · CC BY-SA 3.0
Photo source and identification
Original record · Original image
Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
Michael Gasperl (Migas) · CC BY-SA 3.0
Photo source and identification
Original record · Original image
.jpg){kind=link}
Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
Recognize
Yellow five-petaled flowers with many stamens; small opposite leaves show translucent dots when backlit. N-hypericum-perforatum
Plants & habitat
Seeds and spreading underground stems create persistent patches that can displace native plants. N-hypericum-perforatum
People
Hypericin-containing plant material can cause photosensitivity and dermatitis. The guide does not assess herbal use or medication interactions. N-hypericum-perforatum
Dogs & cats
NC State flags dogs and cats. This source does not establish a pet-specific safe amount. N-hypericum-perforatum
Other animals
Horses are also flagged by the source. Seek veterinary advice before allowing access to contaminated forage. N-hypericum-perforatum
Before taking action
Confirm identification and the requirements of your county weed program. For chemical treatment, follow the current product label, including restrictions around animals and water. S27
References
- CO-rules-2025 — Colorado Noxious Weed Act rules, 8 CCR 1206-2, Colorado Secretary of State / Department of Agriculture. Accessed 2026-09-07T01:07:48+00:00. Locator: Parts 3.1, 4.1, 5.1; management provisions; effective May 15, 2025.
- N-hypericum-perforatum — hypericum perforatum — Plant Toolbox, NC State Extension. Accessed 2026-09-07T01:04:55+00:00. Locator: Description; Attributes; Problems; Poisonous to Humans.
- S27 — 2103 – Colorado Noxious Weeds, PlantTalk Colorado · CSU Extension. Accessed 2026-09-07T00:23:57+00:00. Locator: List A, B and C management categories.