Tansy ragwort

Discuss this plant with the guide — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

Jacobaea vulgaris

Colorado noxious weed · List A — Eradicate. CO-rules-2025

Uncommon in Colorado. All populations are designated for eradication statewide. This is a management category, separate from danger ratings. Category source · What the lists mean.

Poisonous to livestock; harmful alkaloids. Exposure help.

Identification caveat: This is not common tansy or common groundsel. The attempted NC State Jacobaea URL returned a common-groundsel account and was excluded as mismatched evidence.

Still researching this plant

This is a sourced working profile. Evidence is incomplete for People. Identification and source-photo limits are explained below. 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.

Jacobaea vulgaris: An upright flowering plant with yellow heads and deeply divided leaves. — **flowering habit** — An upright flowering plant with yellow heads and deeply divided leaves.
jamie-aa · CC BY 4.0
Photo source and identification
Original record · Original image
Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination.
iNaturalist large server-resized image; no local crop, colour change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

Jacobaea vulgaris: Close view of yellow ray florets and central disks on several heads. — **flower heads** — Close view of yellow ray florets and central disks on several heads.
jamie-aa · CC BY 4.0
Photo source and identification
Original record · Original image
Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination.
iNaturalist large server-resized image; no local crop, colour change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

Jacobaea vulgaris: The green undersides and bracts of flower heads viewed from below. — **head underside** — The green undersides and bracts of flower heads viewed from below.
jamie-aa · CC BY 4.0
Photo source and identification
Original record · Original image
Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination.
iNaturalist large server-resized image; no local crop, colour change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

Recognize

Ruffled, divided leaves and clusters of yellow daisy-like flowerheads, typically with about thirteen ray flowers. WA-tansy-ragwort

Plants & habitat

Seed and regrowth spread plants in disturbed fields and pastures. Mowing alone can produce repeated regrowth. WA-tansy-ragwort

People

All parts contain toxic alkaloids. Do not use the plant in food or home remedies; direct human exposure thresholds are not established here. WA-tansy-ragwort

Dogs & cats

ASPCA lists Senecio species as toxic to dogs and cats, with liver injury from pyrrolizidine alkaloids. Tansy ragwort was formerly Senecio jacobaea; the ASPCA warning is broader than this species and gives no pet-specific dose. A-ragwort WA-tansy-ragwort

Evidence scope: Historical genus-group warning; species-specific alkaloid evidence.

Other animals

All parts are poisonous to livestock. Removed or wilted plants can be more palatable; keep cut material and contaminated forage away from animals. WA-tansy-ragwort

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

This is a statewide eradication priority. Contact your county weed program promptly for identification and an approved management and disposal plan. CO-rules-2025

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.
WA-tansy-ragwort — Tansy Ragwort, Washington State Noxious Weed Control Board. Accessed 2026-09-07T01:09:01+00:00. Locator: Identification, ecological impacts, management; Washington legal class not applied to Colorado.
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.
A-ragwort — Ragwort, ASPCA Poison Control. Accessed 2026-09-07T01:16:20+00:00. Locator: Species identity, description, ecological and exposure evidence; verify group scope.

Content revised 2026-09-07 03:50:00Z · Source checks dated separately in the references.