--- { "id": "annual-sowthistle", "name": "Annual sowthistle", "scientific": "Sonchus oleraceus", "category": "invasive", "status": "Common introduced weed · not on state Lists A/B/C", "status_sources": [ "C-floristic-2020", "CO-rules-2025" ], "warning": "Windborne seed and crop-pest hosting", "warning_tone": "caution", "aliases": [ "common sowthistle", "smooth sowthistle" ], "taxonomy_note": "Separate from prickly sowthistle (Sonchus asper) and the root-spreading perennial sowthistle (Sonchus arvensis). Seedlings can be difficult to separate.", "source_ids": [ "C-floristic-2020", "CO-rules-2025", "U-sowthistle", "S27" ], "description": "Annual sowthistle: Windborne seed and crop-pest hosting. Identification and evidence for Colorado readers.", "claim_evidence": [ { "label": "Identification", "sources": [ "U-sowthistle" ], "scope": "Species-specific", "note": "", "id": "annual-sowthistle-1" }, { "label": "People", "sources": [], "scope": "Review limitation", "note": "", "id": "annual-sowthistle-2" }, { "label": "Dogs & cats", "sources": [], "scope": "Review limitation", "note": "", "id": "annual-sowthistle-3" }, { "label": "Other animals", "sources": [], "scope": "Review limitation", "note": "", "id": "annual-sowthistle-4" }, { "label": "Plants & habitat", "sources": [ "U-sowthistle" ], "scope": "Species ecology; location-limited pest examples", "note": "", "id": "annual-sowthistle-5" }, { "label": "Management & timing", "sources": [ "U-sowthistle" ], "scope": "Management inference from annual seed reproduction", "note": "", "id": "annual-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": "People", "question": "Clarify the human exposure effects and evidence limits described in this section.", "related_claim_ids": [ "annual-sowthistle-2" ] }, { "area": "Dogs & cats", "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.", "related_claim_ids": [ "annual-sowthistle-3" ] }, { "area": "Other animals", "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.", "related_claim_ids": [ "annual-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 oleraceus", "basis": "Included in the 2020 statewide flora assessment. This is not a current county abundance survey.", "source_taxon": "Sonchus oleraceus" }, "source": "content/plants/annual-sowthistle.md" } --- # Annual sowthistle *Sonchus oleraceus* **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) > **Windborne seed and crop-pest hosting.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/). **Identification caveat:** Separate from prickly sowthistle (Sonchus asper) and the root-spreading perennial sowthistle (Sonchus arvensis). Seedlings can be difficult to separate. ## Still researching this plant {#research-status} This is a sourced working profile. Evidence is incomplete for **People, 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 oleraceus: Close view of a pale yellow head composed of many narrow strap-shaped florets.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-sonchus-oleraceus-1.jpg) **flower head** — Close view of a pale yellow head composed of many narrow strap-shaped florets. Photo: Miwasatoshi; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:Sonchus-oleraceus-20080403.JPG); [original image](https://upload.wikimedia.org/wikipedia/commons/5/59/Sonchus-oleraceus-20080403.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. Sow-thistles can overlap in appearance. Source identification is retained; the leaf and fruit views complement the flower view rather than independently proving identity. 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 oleraceus: A deeply lobed middle leaf with a large pointed terminal lobe and toothed edges.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-sonchus-oleraceus-2.jpg) **leaf** — A deeply lobed middle leaf with a large pointed terminal lobe and toothed edges. Photo: T.Voekler; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0); [source record](https://commons.wikimedia.org/wiki/File:S%C3%B3nchus_oler%C3%A1ceus_4562.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/b/b7/S%C3%B3nchus_oler%C3%A1ceus_4562.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. Sow-thistles can overlap in appearance. Source identification is retained; the leaf and fruit views complement the flower view rather than independently proving identity. 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 oleraceus: Several brown fruits with fine white pappus hairs photographed against a dark background.](https://denson.github.io/colorado-weed-field-guide/assets/photos/coverage-hazard-photos-sonchus-oleraceus-3.jpg) **fruits** — Several brown fruits with fine white pappus hairs photographed against a dark background. Photo: Ayotte, Gilles, 1948-; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:Sonchus_oleraceus_15-p.bot-sonch.olera-19.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/9/91/Sonchus_oleraceus_15-p.bot-sonch.olera-19.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. Sow-thistles can overlap in appearance. Source identification is retained; the leaf and fruit views complement the flower view rather than independently proving identity. 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 upright annual with hollow stems, milky sap, yellow flower heads and fluffy seedheads. Upper leaves clasp the stem with pointed, clawlike basal lobes. [U-sowthistle](https://ipm.ucanr.edu/weeds-identification-gallery/annual-sowthistle/) ## People The reviewed sources do not establish species-specific ingestion effects or a safe exposure amount for people. Missing evidence does not establish safety. ## 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 occupies disturbed gardens and cropland and can host aphids and other crop pests. The cited examples are from California; they do not prove a particular Colorado pest outbreak. [U-sowthistle](https://ipm.ucanr.edu/weeds-identification-gallery/annual-sowthistle/) *Evidence scope: Species ecology; location-limited pest examples.* ## Management & timing Prevent plants from producing and dispersing seed. Confirm the species before treating a recurring colony as annual sowthistle. [U-sowthistle](https://ipm.ucanr.edu/weeds-identification-gallery/annual-sowthistle/) *Evidence scope: Management inference from annual seed reproduction.* ## 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. - **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=annual-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 oleraceus. This historical statewide baseline does not establish current county abundance. ## Open research questions - **People:** Clarify the human exposure effects and evidence limits described in this section. - **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 Separate from prickly sowthistle (Sonchus asper) and the root-spreading perennial sowthistle (Sonchus arvensis). Seedlings can be difficult to separate. 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 | |---|---|---|---|---| | annual-sowthistle-1 | Identification | Species-specific | U-sowthistle | No quantitative safe exposure established here. | | annual-sowthistle-2 | People | Review limitation | Review limitation | No quantitative safe exposure established here. | | annual-sowthistle-3 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. | | annual-sowthistle-4 | Other animals | Review limitation | Review limitation | No quantitative safe exposure established here. | | annual-sowthistle-5 | Plants & habitat | Species ecology; location-limited pest examples | U-sowthistle | No quantitative safe exposure established here. | | annual-sowthistle-6 | Management & timing | Management inference from annual seed reproduction | U-sowthistle | 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/annual-sowthistle/ Content revised: 2026-09-07T02:46:00Z Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/annual-sowthistle/index.md Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/annual-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