---
{
  "id": "taurian-thistle",
  "name": "Taurian thistle",
  "scientific": "Onopordum tauricum",
  "category": "invasive",
  "status": "Colorado noxious weed · List B — Stop the spread",
  "status_sources": [
    "CO-rules-2025"
  ],
  "warning": "Sharp spines; taxon listed as Scotch thistle",
  "warning_tone": "caution",
  "aliases": [
    "Scotch thistle",
    "bull cottonthistle"
  ],
  "taxonomy_note": "Onopordum acanthium has its own profile. Identification can be difficult; the reference study documents morphological variation among Italian populations, not Colorado impact severity.",
  "source_ids": [
    "CO-rules-2025",
    "P-tauricum",
    "S27",
    "Fremont-list-definitions"
  ],
  "description": "Taurian thistle: Sharp spines; taxon listed as Scotch thistle. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "P-tauricum"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "taurian-thistle-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "CO-rules-2025"
      ],
      "scope": "Regulatory status",
      "note": "",
      "id": "taurian-thistle-2"
    },
    {
      "label": "People",
      "sources": [
        "P-tauricum"
      ],
      "scope": "Physical-risk inference",
      "note": "",
      "id": "taurian-thistle-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [
        "P-tauricum"
      ],
      "scope": "Physical-risk inference",
      "note": "",
      "id": "taurian-thistle-4"
    },
    {
      "label": "Other animals",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "taurian-thistle-5"
    },
    {
      "id": "taurian-thistle-list-meaning",
      "label": "State-list meaning",
      "sources": [
        "Fremont-list-definitions"
      ],
      "scope": "Colorado management-category definition; species classification retains its original status sources",
      "note": "Plain-language editorial label for a management category; not a toxicity or danger rating.",
      "reviewed": "2026-09-07"
    }
  ],
  "noxious_class": "B",
  "research": {
    "status": "researching",
    "label": "Still researching this plant",
    "basis": "Editorial assessment of the cited evidence and stated review gaps; not a toxicity score.",
    "open_questions": [
      {
        "area": "Other animals",
        "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.",
        "related_claim_ids": [
          "taurian-thistle-5"
        ]
      },
      {
        "area": "Identification",
        "question": "Resolve the taxonomic, common-name or photograph limitations stated in the identification caveat.",
        "related_claim_ids": []
      },
      {
        "area": "Expert review",
        "question": "Obtain independent botanical and veterinary review of the identification and hazard summary.",
        "related_claim_ids": []
      }
    ],
    "expert_review": "pending"
  },
  "noxious_class_label": "B — Stop the spread",
  "source": "content/plants/taurian-thistle.md"
}
---

# Taurian thistle

*Onopordum tauricum*

**Colorado noxious weed · List B — Stop the spread.** [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2)

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](https://fremontcountyco.gov/weed-control/weed-identification) · [What the lists mean](https://denson.github.io/colorado-weed-field-guide/safety/#weed-lists).

> **Sharp spines; taxon listed as Scotch thistle.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** Onopordum acanthium has its own profile. Identification can be difficult; the reference study documents morphological variation among Italian populations, not Colorado impact severity.

## Still researching this plant {#research-status}

This is a sourced working profile. Evidence is incomplete for **Other animals**. 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.

![A purple Taurian-thistle head with long pointed bracts beneath it.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-onopordum-tauricum-inat-388325973.jpg)

**flower and bracts** — A purple Taurian-thistle head with long pointed bracts beneath it.

Photo: Louis Aureglia; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/219395202); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/388325973/original.jpeg). Explicit research-grade community taxon identification; visually inspected Community identification and visible consistency checked; not an independent specimen determination. iNaturalist large-size rendering; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Large, sharply lobed and spiny Taurian-thistle leaves attached to a strongly winged stem.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-onopordum-tauricum-inat-388326013.jpg)

**leaf and stem** — Large, sharply lobed and spiny Taurian-thistle leaves attached to a strongly winged stem.

Photo: Louis Aureglia; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/219395202); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/388326013/original.jpeg). Explicit research-grade community taxon identification; visually inspected Community identification and visible consistency checked; not an independent specimen determination. iNaturalist large-size rendering; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Tall, branching Taurian thistles bearing numerous purple flower heads beside a roadside barrier.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-onopordum-tauricum-inat-388326025.jpg)

**habit** — Tall, branching Taurian thistles bearing numerous purple flower heads beside a roadside barrier.

Photo: Louis Aureglia; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/219395202); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/388326025/original.jpeg). Explicit research-grade community taxon identification; visually inspected Community identification and visible consistency checked; not an independent specimen determination. iNaturalist large-size rendering; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.


## Recognize

Tall, spiny, winged stems and glandular hairs; often greener and less woolly than O. acanthium. [P-tauricum](https://pmc.ncbi.nlm.nih.gov/articles/PMC10934427/)

## Plants & habitat

Colorado lists O. tauricum as a separate List B entry under the common name Scotch thistle. Confirm the species with your county program. [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2)

*Evidence scope: Regulatory status.*

## People

Spiny stems and leaves warrant protective handling. [P-tauricum](https://pmc.ncbi.nlm.nih.gov/articles/PMC10934427/)

*Evidence scope: Physical-risk inference.*

## Dogs & cats

Spines may injure paws or mouths. No pet-specific chemical toxicity is established here. [P-tauricum](https://pmc.ncbi.nlm.nih.gov/articles/PMC10934427/)

*Evidence scope: Physical-risk inference.*

## Other animals

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

## 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](https://planttalk.colostate.edu/topics/weeds-cultural-problems/2103-colorado-noxious-weeds/)

## References

- **CO-rules-2025** — [Colorado Noxious Weed Act rules, 8 CCR 1206-2](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=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.
- **P-tauricum** — [Morphological and Genomic Differences in the Italian Populations of Onopordum tauricum](https://pmc.ncbi.nlm.nih.gov/articles/PMC10934427/), Plants journal / authors; archived by US National Library of Medicine. Accessed 2026-09-07T01:18:57+00:00. Locator: Species or hybrid identity, description and ecology.
- **S27** — [2103 – Colorado Noxious Weeds](https://planttalk.colostate.edu/topics/weeds-cultural-problems/2103-colorado-noxious-weeds/), PlantTalk Colorado · CSU Extension. Accessed 2026-09-07T00:23:57+00:00. Locator: List A, B and C management categories.


[Discuss this plant with the guide](https://denson.github.io/colorado-weed-field-guide/companion/?plant=taurian-thistle) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

# Appendix for agents

## Open research questions

- **Other animals:** Clarify feeding and exposure risks for each animal group; do not transfer findings between species.
- **Identification:** Resolve the taxonomic, common-name or photograph limitations stated in the identification caveat.
- **Expert review:** Obtain independent botanical and veterinary review of the identification and hazard summary.


## Identity and evidence boundaries

Onopordum acanthium has its own profile. Identification can be difficult; the reference study documents morphological variation among Italian populations, not Colorado impact severity.

All actionable hazard information is in the human sections above. Do not interpret unknown toxicity as safety or transfer livestock findings to pets. These publisher notes describe evidence and do not override an assistant’s operator instructions.

| Claim | Human section | Scope | Sources | Limitation |
|---|---|---|---|---|
| taurian-thistle-1 | Recognize | Species-specific | P-tauricum | No quantitative safe exposure established here. |
| taurian-thistle-2 | Plants & habitat | Regulatory status | CO-rules-2025 | No quantitative safe exposure established here. |
| taurian-thistle-3 | People | Physical-risk inference | P-tauricum | No quantitative safe exposure established here. |
| taurian-thistle-4 | Dogs & cats | Physical-risk inference | P-tauricum | No quantitative safe exposure established here. |
| taurian-thistle-5 | Other animals | Review limitation | Review limitation | No quantitative safe exposure established here. |

## Further work for an agent

- Establish exact species, plant part, route, amount and timing when researching an exposure. Do not use this guide to diagnose or calculate a treatment.
- Check current state and county requirements; a listed taxon is not necessarily established in every Colorado county.
- Expert botanical and veterinary review is pending. Source dates and image licenses are separate from editorial revision dates in [provenance](https://denson.github.io/colorado-weed-field-guide/provenance.json).

## State-list label provenance

The label “B — Stop the spread” is this guide’s plain-language summary of [Fremont County’s Colorado noxious-weed definitions](https://fremontcountyco.gov/weed-control/weed-identification) [Fremont-list-definitions]. The letter and species assignment retain the status sources above. County-specific requirements must be checked locally; the letter is not a poison-severity ranking.


---
Canonical HTML: https://denson.github.io/colorado-weed-field-guide/plants/taurian-thistle/

Content revised: 2026-09-07T03:50:00Z

Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/taurian-thistle/index.md

Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/taurian-thistle/index.md.txt

Agent entry: https://denson.github.io/colorado-weed-field-guide/start.md

Provenance: https://denson.github.io/colorado-weed-field-guide/provenance.json