Yellow starthistle

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

Centaurea solstitialis

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.

Severe horse poisoning; sharp spines. Exposure help.

Identification caveat: A horse-specific poisoning hazard is established. Do not generalize controlled grazing by other livestock into unrestricted feeding advice.

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.

Centaurea solstitialis: A bright yellow flower head beside a dry head, showing the long radiating spines. — **flower and spines** — A bright yellow flower head beside a dry head, showing the long radiating spines.
Юрий Данилевский (Yuriy Danilevsky) · 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.

Centaurea solstitialis: Close view of a strongly spined head and narrow leaves on a winged-looking stem. — **spines and foliage** — Close view of a strongly spined head and narrow leaves on a winged-looking stem.
Eleftherios Katsillis · 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.

Centaurea solstitialis: A tall, branching, yellow-flowered plant standing in dry grassland. — **flowering habit** — A tall, branching, yellow-flowered plant standing in dry grassland.
Юрий Данилевский (Yuriy Danilevsky) · 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

An annual with yellow flowerheads surrounded by long, radiating spines and gray-green foliage. N-centaurea-solstitialis

Plants & habitat

Spreads by seed into rangelands and disturbed ground. Prevent seed set and keep contaminated material out of horse feed. N-centaurea-solstitialis

People

Long flowerhead spines present a puncture hazard; use protective handling. N-centaurea-solstitialis

Dogs & cats

Spines may injure mouths or paws. Horse poisoning findings do not establish a pet-specific toxic dose. N-centaurea-solstitialis

Other animals

Ingestion can cause devastating loss of chewing and swallowing function in horses. Suspected exposure warrants veterinary assessment. N-centaurea-solstitialis

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.
N-centaurea-solstitialis — centaurea solstitialis — 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.