--- { "id": "plumeless-thistle", "name": "Plumeless thistle", "scientific": "Carduus acanthoides", "category": "invasive", "status": "Colorado noxious weed · List B — Stop the spread", "status_sources": [ "CO-rules-2025" ], "warning": "Sharp spines; pasture competition", "warning_tone": "caution", "aliases": [], "taxonomy_note": "Distinguish introduced Carduus from Colorado’s native thistles before removal.", "source_ids": [ "CO-rules-2025", "J-plumeless-thistle", "S27", "Fremont-list-definitions" ], "description": "Plumeless thistle: Sharp spines; pasture competition. Identification and evidence for Colorado readers.", "claim_evidence": [ { "label": "Recognize", "sources": [ "J-plumeless-thistle" ], "scope": "Species-specific", "note": "", "id": "plumeless-thistle-1" }, { "label": "Plants & habitat", "sources": [ "J-plumeless-thistle" ], "scope": "Species-specific", "note": "", "id": "plumeless-thistle-2" }, { "label": "People", "sources": [ "J-plumeless-thistle" ], "scope": "Physical-risk inference", "note": "", "id": "plumeless-thistle-3" }, { "label": "Dogs & cats", "sources": [ "J-plumeless-thistle" ], "scope": "Physical-risk inference; ingestion evidence gap", "note": "", "id": "plumeless-thistle-4" }, { "label": "Other animals", "sources": [], "scope": "Review limitation", "note": "", "id": "plumeless-thistle-5" }, { "id": "plumeless-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": "Dogs & cats", "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.", "related_claim_ids": [ "plumeless-thistle-4" ] }, { "area": "Other animals", "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.", "related_claim_ids": [ "plumeless-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/plumeless-thistle.md" } --- # Plumeless thistle *Carduus acanthoides* **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; pasture competition.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/). **Identification caveat:** Distinguish introduced Carduus from Colorado’s native thistles before removal. ## Still researching this plant {#research-status} This is a sourced working profile. Evidence is incomplete for **Dogs & cats, 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. ![Flatbed photographic scan of a deeply lobed, spiny plumeless-thistle leaf with a millimeter scale.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-carduus-acanthoides-01.jpg) **leaf** — Flatbed photographic scan of a deeply lobed, spiny plumeless-thistle leaf with a millimeter scale. Photo: Dmitry Makeev; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:2020_year._Herbarium._Carduus_acanthoides._img-009.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/7/74/2020_year._Herbarium._Carduus_acanthoides._img-009.jpg). Source-identified photograph with visual consistency check Carduus acanthoides. 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. ![Pink-purple plumeless-thistle flower heads above an extensively winged, spiny stem.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-carduus-acanthoides-04.jpg) **flowering stem** — Pink-purple plumeless-thistle flower heads above an extensively winged, spiny stem. Photo: Robert Flogaus-Faust; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0); [source record](https://commons.wikimedia.org/wiki/File:Carduus_acanthoides_2_RF.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/4/4d/Carduus_acanthoides_2_RF.jpg). Source-identified photograph with visual consistency check Spiny plumeless thistle ( Carduus acanthoides ), near Groß-Gerau-Wallerstädten at the bike path along L3094, Germany 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. ![Purple plumeless-thistle heads beside a mature head releasing pale feathery seed structures.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-carduus-acanthoides-05.jpg) **flowers and seed dispersal** — Purple plumeless-thistle heads beside a mature head releasing pale feathery seed structures. Photo: Robert Flogaus-Faust; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0); [source record](https://commons.wikimedia.org/wiki/File:Carduus_acanthoides_4_RF.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/2/26/Carduus_acanthoides_4_RF.jpg). Source-identified photograph with visual consistency check Spiny plumeless thistle ( Carduus acanthoides ) at the bike path between Egelsbach and Erzhausen , Germany 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 A spiny thistle with winged stems and relatively small, reddish-purple flowerheads. [J-plumeless-thistle](https://www.jeffco.us/2294/Plumeless-Thistle) ## Plants & habitat Spreads by seed through disturbed pasture and roadsides. Follow-up is needed as rosettes germinate. [J-plumeless-thistle](https://www.jeffco.us/2294/Plumeless-Thistle) ## People Spines on leaves, stems and flowerhead bracts can puncture skin; use protective handling. [J-plumeless-thistle](https://www.jeffco.us/2294/Plumeless-Thistle) *Evidence scope: Physical-risk inference.* ## Dogs & cats Spines may injure mouths or paws. Pet-specific chemical toxicity is not established here. [J-plumeless-thistle](https://www.jeffco.us/2294/Plumeless-Thistle) *Evidence scope: Physical-risk inference; ingestion evidence gap.* ## 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. - **J-plumeless-thistle** — [Plumeless Thistle](https://www.jeffco.us/2294/Plumeless-Thistle), Jefferson County, Colorado. Accessed 2026-09-07T00:27:24+00:00. Locator: Description, impacts, Colorado list designation, management. - **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=plumeless-thistle) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care. # Appendix for agents ## Open research questions - **Dogs & cats:** Find species-specific dog and cat exposure evidence; do not infer safety from missing reports. - **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 Distinguish introduced Carduus from Colorado’s native thistles before removal. 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 | |---|---|---|---|---| | plumeless-thistle-1 | Recognize | Species-specific | J-plumeless-thistle | No quantitative safe exposure established here. | | plumeless-thistle-2 | Plants & habitat | Species-specific | J-plumeless-thistle | No quantitative safe exposure established here. | | plumeless-thistle-3 | People | Physical-risk inference | J-plumeless-thistle | No quantitative safe exposure established here. | | plumeless-thistle-4 | Dogs & cats | Physical-risk inference; ingestion evidence gap | J-plumeless-thistle | No quantitative safe exposure established here. | | plumeless-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/plumeless-thistle/ Content revised: 2026-09-07T03:50:00Z Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/plumeless-thistle/index.md Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/plumeless-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