---
{
  "id": "perennial-sowthistle",
  "name": "Perennial sowthistle",
  "scientific": "Sonchus arvensis",
  "category": "invasive",
  "status": "Colorado noxious weed · List C — Manage widespread weeds",
  "status_sources": [
    "CO-rules-2025"
  ],
  "warning": "Persistent underground spread",
  "warning_tone": "caution",
  "aliases": [],
  "taxonomy_note": "Annual sowthistles are separate species. A yellow flowerhead and milky sap are insufficient identification.",
  "source_ids": [
    "CO-rules-2025",
    "J-perennial-sowthistle",
    "S27",
    "Fremont-list-definitions"
  ],
  "description": "Perennial sowthistle: Persistent underground spread. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "J-perennial-sowthistle"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "perennial-sowthistle-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "J-perennial-sowthistle"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "perennial-sowthistle-2"
    },
    {
      "label": "People",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "perennial-sowthistle-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "perennial-sowthistle-4"
    },
    {
      "label": "Other animals",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "perennial-sowthistle-5"
    },
    {
      "id": "perennial-sowthistle-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": "C",
  "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": [
          "perennial-sowthistle-3"
        ]
      },
      {
        "area": "Dogs & cats",
        "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
        "related_claim_ids": [
          "perennial-sowthistle-4"
        ]
      },
      {
        "area": "Other animals",
        "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.",
        "related_claim_ids": [
          "perennial-sowthistle-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": "C — Manage widespread weeds",
  "source": "content/plants/perennial-sowthistle.md"
}
---

# Perennial sowthistle

*Sonchus arvensis*

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

Widespread and well established. Control is recommended by the state; local governments may require management. 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).

> **Persistent underground spread.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** Annual sowthistles are separate species. A yellow flowerhead and milky sap are insufficient identification.

## 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 arvensis: Branched upright sowthistle bearing yellow flower heads above deeply lobed foliage.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-sonchus-arvensis-08-05-habit.jpg)

**habit** — Branched upright sowthistle bearing yellow flower heads above deeply lobed foliage.

Photo: Gabriele Kothe-Heinrich; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0); [source record](https://commons.wikimedia.org/wiki/File:Sonchus_arvensis_Helgoland.JPG); [original image](https://upload.wikimedia.org/wikipedia/commons/b/b4/Sonchus_arvensis_Helgoland.JPG). Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Sonchus arvensis: Long blue-green toothed leaf with a clasping base around an upright stem.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-sonchus-arvensis-08-07-leaf.jpg)

**leaf** — Long blue-green toothed leaf with a clasping base around an upright stem.

Photo: Anneli Salo; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0); [source record](https://commons.wikimedia.org/wiki/File:Sonchus_arvensis_Peltovalvatti_C_H8939.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/4/42/Sonchus_arvensis_Peltovalvatti_C_H8939.jpg). Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Sonchus arvensis: A yellow head composed of many narrow strap-shaped florets.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-sonchus-arvensis-08-11-flower.jpg)

**flower** — A yellow head composed of many narrow strap-shaped florets.

Photo: Bogdan; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/); [source record](https://commons.wikimedia.org/wiki/File:Sonchus_arvensis_2_bgiu.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/4/46/Sonchus_arvensis_2_bgiu.jpg). Source page scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.


## Recognize

Yellow dandelion-like flowerheads on leafy stalks; leaves clasp the stem and may have prickly margins. [J-perennial-sowthistle](https://www.jeffco.us/2323/Perennial-Sowthistle)

## Plants & habitat

A perennial of moist disturbed places with spreading underground growth. Seed prevention and repeated follow-up are needed. [J-perennial-sowthistle](https://www.jeffco.us/2323/Perennial-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. 

## 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-perennial-sowthistle** — [Perennial Sowthistle](https://www.jeffco.us/2323/Perennial-Sowthistle), 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=perennial-sowthistle) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

# Appendix for agents

## 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

Annual sowthistles are separate species. A yellow flowerhead and milky sap are insufficient identification.

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 |
|---|---|---|---|---|
| perennial-sowthistle-1 | Recognize | Species-specific | J-perennial-sowthistle | No quantitative safe exposure established here. |
| perennial-sowthistle-2 | Plants & habitat | Species-specific | J-perennial-sowthistle | No quantitative safe exposure established here. |
| perennial-sowthistle-3 | People | Review limitation | Review limitation | No quantitative safe exposure established here. |
| perennial-sowthistle-4 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. |
| perennial-sowthistle-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 “C — Manage widespread weeds” 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/perennial-sowthistle/

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

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

Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/perennial-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