Common tansy

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

Tanacetum vulgare

Colorado noxious weed · List B — Stop the spread. CO-rules-2025

Established in some areas. Requirements vary by location: eradication, containment or suppression to stop further spread. This is a management category, separate from danger ratings. Category source · What the lists mean.

Toxic ingestion; contact dermatitis. Exposure help.

Identification caveat: Common tansy is not tansy ragwort (Jacobaea vulgaris). Their chemical hazards and flower structures differ.

Still researching this plant

This is a sourced working profile. Evidence is incomplete for Dogs & cats. 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.

**flowers** — Close view of three yellow buttonlike tansy flower heads, showing tiny disk florets.
Agnes Monkelbaan · CC BY-SA 4.0
Photo source and identification
Original record · Original image
Source-identified photograph with visual consistency check Flowers of Tansy ( Tanacetum vulgare ). Focus stack of 28 photos. Source labeling and visible consistency checked; not an independent specimen determination.
Wikimedia-generated thumbnail rescaling only; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

**leaf** — Flatbed photographic scan of a deeply divided, toothed tansy leaf with a millimeter scale.
Dmitry Makeev · CC BY-SA 4.0
Photo source and identification
Original record · Original image
Source-identified photograph with visual consistency check Tanacetum vulgare. Leaf adaxial side. Herbarium of the city Elektrostal Moscow Oblast, 2020 year. Created by scanography. Collection D.Makeev. Scale 1 unit = 1 mm. These are original colors. Please do not make edit. Source labeling and visible consistency checked; not an independent specimen determination.
Wikimedia-generated thumbnail rescaling only; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

**flowering stem** — An upright tansy stem with divided leaves and clusters of yellow buttonlike flowers.
Benjamin Zwittnig · CC BY 2.5 si
Photo source and identification
Original record · Original image
Source-identified photograph with visual consistency check Navadni vratič na Limbarski gori. Source labeling and visible consistency checked; not an independent specimen determination.
Wikimedia-generated thumbnail rescaling only; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

Recognize

Fern-like leaves and flat clusters of yellow, button-like flowerheads without showy ray petals. N-tanacetum-vulgare

Plants & habitat

Seeds, rhizomes and root fragments build dense stands that displace other plants and degrade pastures. N-tanacetum-vulgare

People

Thujone can cause serious poisoning, including convulsions, and the plant can irritate skin. Avoid teas and home remedies. N-tanacetum-vulgare

Dogs & cats

The reviewed sources do not establish species-specific ingestion effects or a safe exposure amount for dogs or cats. Missing evidence does not establish safety.

Other animals

Toxicity is reported for horses and cattle. Specialist grazing by other animals is not a general feeding recommendation. N-tanacetum-vulgare

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-tanacetum-vulgare — tanacetum vulgare — Plant Toolbox, NC State Extension. Accessed 2026-09-07T01:04:53+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.

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