--- { "id": "prickly-sowthistle", "name": "Prickly sowthistle", "scientific": "Sonchus asper", "category": "invasive", "status": "Common introduced weed · not on state Lists A/B/C", "status_sources": [ "C-floristic-2020", "CO-rules-2025" ], "warning": "Spiny leaves and rapid seed production", "warning_tone": "caution", "aliases": [ "spiny sowthistle" ], "taxonomy_note": "This is an annual Sonchus, not a true Cirsium thistle and not perennial sowthistle. Confirm leaf bases and life cycle.", "source_ids": [ "C-floristic-2020", "CO-rules-2025", "N-sonchus-asper", "U-sowthistle", "S27" ], "description": "Prickly sowthistle: Spiny leaves and rapid seed production. Identification and evidence for Colorado readers.", "claim_evidence": [ { "label": "Identification", "sources": [ "N-sonchus-asper", "U-sowthistle" ], "scope": "Species-specific", "note": "", "id": "prickly-sowthistle-1" }, { "label": "People", "sources": [ "N-sonchus-asper" ], "scope": "Handling precaution inferred from leaf structure", "note": "", "id": "prickly-sowthistle-2" }, { "label": "Dogs & cats", "sources": [], "scope": "Review limitation", "note": "", "id": "prickly-sowthistle-3" }, { "label": "Other animals", "sources": [], "scope": "Review limitation", "note": "", "id": "prickly-sowthistle-4" }, { "label": "Plants & habitat", "sources": [ "N-sonchus-asper" ], "scope": "Species-specific", "note": "", "id": "prickly-sowthistle-5" }, { "label": "Management & timing", "sources": [ "N-sonchus-asper" ], "scope": "Species-specific", "note": "", "id": "prickly-sowthistle-6" } ], "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": [ "prickly-sowthistle-3" ] }, { "area": "Other animals", "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.", "related_claim_ids": [ "prickly-sowthistle-4" ] }, { "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" }, "colorado_relevance": { "source_id": "C-floristic-2020", "locator": "Appendix B; PDF page 80; Sonchus asper", "basis": "Included in the 2020 statewide flora assessment. This is not a current county abundance survey.", "source_taxon": "Sonchus asper" }, "source": "content/plants/prickly-sowthistle.md" } --- # Prickly sowthistle *Sonchus asper* **Common introduced weed · not on state Lists A/B/C.** [C-floristic-2020](https://cnhp.colostate.edu/download/documents/2020/CO_FQA_2020_Final_Report.pdf) [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2) > **Spiny leaves and rapid seed production.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/). **Identification caveat:** This is an annual Sonchus, not a true Cirsium thistle and not perennial sowthistle. Confirm leaf bases and life cycle. ## 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. ![Sonchus asper: A tall flowering prickly sow-thistle with lobed leaves beside a tree trunk.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-sonchus-asper-1.jpg) **habit** — A tall flowering prickly sow-thistle with lobed leaves beside a tree trunk. Photo: Didier Descouens; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:(MHNT)_Sonchus_asper_-_Plant_habit.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/7/73/%28MHNT%29_Sonchus_asper_-_Plant_habit.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Source identification is retained. The rounded clasping leaf lobes and prickly leaf edges are shown for comparison with S. oleraceus; hybrids and other lookalikes require a full key. Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop. ![Sonchus asper: Glossy, spine-toothed leaves clasping the stem with rounded basal lobes.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-sonchus-asper-2.jpg) **leaf attachment** — Glossy, spine-toothed leaves clasping the stem with rounded basal lobes. Photo: Douglas Goldman; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/); [source record](https://www.inaturalist.org/observations/138412061); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/236567927/original.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Source identification is retained. The rounded clasping leaf lobes and prickly leaf edges are shown for comparison with S. oleraceus; hybrids and other lookalikes require a full key. iNaturalist large server-resized photo; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop. ![Sonchus asper: A rounded white pappus head ready to release its fruits.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-sonchus-asper-3.jpg) **seed head** — A rounded white pappus head ready to release its fruits. Photo: Matt Lavin from Bozeman, Montana, USA; [CC BY-SA 2.0](https://creativecommons.org/licenses/by-sa/2.0); [source record](https://commons.wikimedia.org/wiki/File:Sonchus_asper_(4971087345).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/4/49/Sonchus_asper_%284971087345%29.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Source identification is retained. The rounded clasping leaf lobes and prickly leaf edges are shown for comparison with S. oleraceus; hybrids and other lookalikes require a full key. Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop. ## Identification An annual with yellow flower heads and often glossy, prickly-edged leaves. Rounded basal leaf lobes clasp the stem, unlike the more pointed lobes of annual sowthistle. [N-sonchus-asper](https://plants.ces.ncsu.edu/plants/sonchus-asper/) [U-sowthistle](https://ipm.ucanr.edu/weeds-identification-gallery/annual-sowthistle/) ## People Spiny leaf edges warrant care when handling. No ingestion safety has been established here. [N-sonchus-asper](https://plants.ces.ncsu.edu/plants/sonchus-asper/) *Evidence scope: Handling precaution inferred from leaf structure.* ## 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 The reviewed sources do not establish species-specific ingestion effects or a safe exposure amount for livestock. Missing evidence does not establish safety. ## Plants & habitat It grows in gardens, roadsides and disturbed ground. Plants can bolt quickly, and seeds travel by wind and water. [N-sonchus-asper](https://plants.ces.ncsu.edu/plants/sonchus-asper/) ## Management & timing Inspect patches often and remove unwanted plants before fluffy seedheads form. [N-sonchus-asper](https://plants.ces.ncsu.edu/plants/sonchus-asper/) ## 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 - **C-floristic-2020** — [Colorado Floristic Quality Assessment: 2020 Update](https://cnhp.colostate.edu/download/documents/2020/CO_FQA_2020_Final_Report.pdf), Colorado Natural Heritage Program, Colorado State University. Accessed 2026-09-07T02:27:33+00:00. Locator: Appendix B, Colorado species list: scientific name and native/non-native fields. - **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. - **N-sonchus-asper** — [Sonchus asper](https://plants.ces.ncsu.edu/plants/sonchus-asper/), NC State Extension. Accessed 2026-09-07T02:23:12+00:00. Locator: Description, identification attributes and plant problems; toxicity section where present. - **U-sowthistle** — [Annual sowthistle](https://ipm.ucanr.edu/weeds-identification-gallery/annual-sowthistle/), University of California Statewide Integrated Pest Management. Accessed 2026-09-07T02:26:10+00:00. Locator: Named species or genus; identification, distribution and hazard sections where available. - **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=prickly-sowthistle) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care. # Appendix for agents Colorado inclusion: [C-floristic-2020](https://cnhp.colostate.edu/download/documents/2020/CO_FQA_2020_Final_Report.pdf), Appendix B; PDF page 80; Sonchus asper. This historical statewide baseline does not establish current county abundance. ## 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 This is an annual Sonchus, not a true Cirsium thistle and not perennial sowthistle. Confirm leaf bases and life cycle. 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 | |---|---|---|---|---| | prickly-sowthistle-1 | Identification | Species-specific | N-sonchus-asper, U-sowthistle | No quantitative safe exposure established here. | | prickly-sowthistle-2 | People | Handling precaution inferred from leaf structure | N-sonchus-asper | No quantitative safe exposure established here. | | prickly-sowthistle-3 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. | | prickly-sowthistle-4 | Other animals | Review limitation | Review limitation | No quantitative safe exposure established here. | | prickly-sowthistle-5 | Plants & habitat | Species-specific | N-sonchus-asper | No quantitative safe exposure established here. | | prickly-sowthistle-6 | Management & timing | Species-specific | N-sonchus-asper | 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). --- Canonical HTML: https://denson.github.io/colorado-weed-field-guide/plants/prickly-sowthistle/ Content revised: 2026-09-07T02:46:00Z Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/prickly-sowthistle/index.md Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/prickly-sowthistle/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