St. John's wort (klamathweed)
Hypericum perforatum
- Plant type
- forb
- Settings
- Rangeland, Disturbed ground
- Risk
- Moderate risk Our rating from the cited sources.
- Review
- Not yet reviewed by a veterinarian.
Photos
Planned.
How to tell it
Usually about 1.5 ft tall, up to 6 ft; leaves covered with small clear dots; clusters of five-petal orange-yellow flowers with black dots on the edges; dry gravelly or sandy soil in full sun (ARS).
Look-alikes: Planned.
What to do on a site walk
- Limit time.
- Keep white or freshly shorn goats off dense stands in full sun.
- Shade any affected goat.
Why it matters
- Toxic principle
- Hypericin (photosensitizer)
- Toxic parts
- All parts
- Basis for our rating
- Chewgrass rating. ARS: causes sunburn-like damage, seldom fatal. Cornell and Merck list goats. ARS notes freshly sheared sheep are most at risk, so treat freshly shorn white or mohair goats with care.
Signs in goats
Sunburn on white or thin-haired skin, rubbing the head, seeking shade, swollen eyelids and ears, peeling skin (ARS).
If you think an animal has been poisoned, call your vet right away.
Season
Toxic at all stages; young spring shoots and contaminated hay (ARS).
Sources
- USDA ARS Poisonous Plant Research Lab: St. Johnswort
- Second source (poisonousplants.ansci.cornell.edu)
Links last checked: 2026-10-31