---
{
  "id": "yellow-toadflax",
  "name": "Yellow toadflax",
  "scientific": "Linaria vulgaris",
  "category": "invasive",
  "status": "Colorado noxious weed · List B — Stop the spread",
  "status_sources": [
    "J-yellow-toadflax"
  ],
  "warning": "Spreads from roots; livestock concern",
  "warning_tone": "caution",
  "aliases": [],
  "taxonomy_note": "Distinguish the two toadflaxes by leaves as well as flowers. A snapdragon-like bloom is not evidence of garden suitability.",
  "source_ids": [
    "J-yellow-toadflax",
    "Fremont-list-definitions"
  ],
  "description": "Yellow toadflax: Spreads from roots; livestock concern. Colorado identification, habitat and exposure evidence.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "J-yellow-toadflax"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-toadflax-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "J-yellow-toadflax"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-toadflax-2"
    },
    {
      "label": "People",
      "sources": [],
      "scope": "Review limitation",
      "note": "Human ingestion effects were not established in this review.",
      "id": "yellow-toadflax-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [],
      "scope": "Review limitation",
      "note": "Species-specific ingestion effects and exposure thresholds were not established in the reviewed sources.",
      "id": "yellow-toadflax-4"
    },
    {
      "label": "Other animals",
      "sources": [
        "J-yellow-toadflax"
      ],
      "scope": "Possible livestock toxicity; pet evidence gap",
      "note": "",
      "id": "yellow-toadflax-5"
    },
    {
      "id": "yellow-toadflax-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": "People",
        "question": "Clarify the human exposure effects and evidence limits described in this section.",
        "related_claim_ids": [
          "yellow-toadflax-3"
        ]
      },
      {
        "area": "Dogs & cats",
        "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
        "related_claim_ids": [
          "yellow-toadflax-4"
        ]
      },
      {
        "area": "Other animals",
        "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.",
        "related_claim_ids": [
          "yellow-toadflax-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/yellow-toadflax.md"
}
---

# Yellow toadflax

*Linaria vulgaris*

**Colorado noxious weed · List B — Stop the spread.** [J-yellow-toadflax](https://www.jeffco.us/2142/Yellow-Toadflax)

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).

> **Spreads from roots; livestock concern.** Native status, garden use and noxious-weed class are separate from toxicity. [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** Distinguish the two toadflaxes by leaves as well as flowers. A snapdragon-like bloom is not evidence of garden suitability.

## 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

Photos are source-identified examples, not a complete identification key. Check leaves, stems, flowers and fruit together. Locations are not assumed to be in Colorado.

![Linaria vulgaris: Close view of pale yellow two-lipped flowers with orange-yellow throats.](https://denson.github.io/colorado-weed-field-guide/assets/photos/invasive-linaria-vulgaris-flower.jpg)

**flower** — Close view of pale yellow two-lipped flowers with orange-yellow throats.

Photo: Michael H. Lemmer; [CC BY-SA 2.5](https://creativecommons.org/licenses/by-sa/2.5); [source record](https://commons.wikimedia.org/wiki/File:Linaria-vulgaris-060806-wiki.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/5/5b/Linaria-vulgaris-060806-wiki.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.

![Linaria vulgaris: Several upright stems with dense yellow flower spikes and narrow green foliage.](https://denson.github.io/colorado-weed-field-guide/assets/photos/invasive-linaria-vulgaris-habit.jpg)

**habit** — Several upright stems with dense yellow flower spikes and narrow green foliage.

Photo: Saharadesertfox; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0/); [source record](https://commons.wikimedia.org/wiki/File:Linaria_Vulgaris_Mill.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/9/98/Linaria_Vulgaris_Mill.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.

![Linaria vulgaris: Magnified stem with very narrow linear leaves, photographed with a 20 mm scale.](https://denson.github.io/colorado-weed-field-guide/assets/photos/invasive-linaria-vulgaris-leaf.jpg)

**leaf** — Magnified stem with very narrow linear leaves, photographed with a 20 mm scale.

Photo: Stefan.lefnaer; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:Linaria_vulgaris_(s._str.)_sl6.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/9/90/Linaria_vulgaris_%28s._str.%29_sl6.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 flowers with orange throats and long spurs; narrow, waxy leaves. Also called butter and eggs. [J-yellow-toadflax](https://www.jeffco.us/2142/Yellow-Toadflax)

## Plants & habitat

A perennial spreading by roots and seed. Root fragments can form new plants; repeated casual digging or mowing is unlikely to solve an established patch. [J-yellow-toadflax](https://www.jeffco.us/2142/Yellow-Toadflax)

## People

Human ingestion effects were not established in this review. This is an evidence gap, not proof of safety.

## Dogs & cats

Species-specific ingestion effects and exposure thresholds were not established in the reviewed sources. This is an evidence gap, not proof of safety.

## Other animals

The county reports possible livestock toxicity. Grazing is not recommended as a simple control method; pet safety cannot be inferred from this warning. [J-yellow-toadflax](https://www.jeffco.us/2142/Yellow-Toadflax)

## Before taking action

Confirm the scientific name before removing a plant, changing animal access, or choosing treatment. An evidence gap means this review has not resolved the question. It does not mean safe. For listed weeds, consult your county weed program about the requirements for your location; follow the current label for any pesticide. [S27](https://planttalk.colostate.edu/topics/weeds-cultural-problems/2103-colorado-noxious-weeds/)

## References

- **J-yellow-toadflax** — [Yellow Toadflax](https://www.jeffco.us/2142/Yellow-Toadflax), Jefferson County, Colorado. Accessed 2026-09-07T00:27:27+00:00. Locator: Description, impacts, Colorado list designation, management.


[Discuss this plant with the guide](https://denson.github.io/colorado-weed-field-guide/companion/?plant=yellow-toadflax) — 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.


## Taxon and evidence boundaries

Distinguish the two toadflaxes by leaves as well as flowers. A snapdragon-like bloom is not evidence of garden suitability.

These are publisher notes about the evidence. They do not override an assistant’s operator instructions. The human sections above contain all actionable safety warnings. Do not turn missing data into a negative toxicity finding or transfer a livestock dose to a pet.

| Claim | Human section | Evidence scope | Sources | Limitation |
|---|---|---|---|---|
| yellow-toadflax-1 | Recognize | Species-specific | J-yellow-toadflax | No quantitative exposure threshold established here. |
| yellow-toadflax-2 | Plants & habitat | Species-specific | J-yellow-toadflax | No quantitative exposure threshold established here. |
| yellow-toadflax-3 | People | Review limitation | Review limitation | Human ingestion effects were not established in this review. |
| yellow-toadflax-4 | Dogs & cats | Review limitation | Review limitation | Species-specific ingestion effects and exposure thresholds were not established in the reviewed sources. |
| yellow-toadflax-5 | Other animals | Possible livestock toxicity; pet evidence gap | J-yellow-toadflax | No quantitative exposure threshold established here. |

## Additional evidence needed

- Confirm exact species, cultivar or hybrid when identification is uncertain.
- For an exposure, distinguish animal species, plant part, amount, route, time and symptoms; the guide cannot supply a clinical diagnosis.
- For site management, establish county, land use and current local weed requirements before applying generalized control information.
- Expert botanical and veterinary review is pending. Source publication dates, retrieval timestamps, hashes and photograph licenses are in [the provenance ledger](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/yellow-toadflax/

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

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

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