---
{
  "id": "yellow-flag-iris",
  "name": "Yellow flag iris",
  "scientific": "Iris pseudacorus",
  "category": "invasive",
  "status": "Colorado noxious weed · List A — Eradicate",
  "status_sources": [
    "CO-rules-2025"
  ],
  "warning": "Ingestion concern; invasive wetland colonies",
  "warning_tone": "danger",
  "aliases": [],
  "taxonomy_note": "",
  "source_ids": [
    "CO-rules-2025",
    "N-iris-pseudacorus",
    "S27",
    "Fremont-list-definitions"
  ],
  "description": "Yellow flag iris: Ingestion concern; invasive wetland colonies. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "N-iris-pseudacorus"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-flag-iris-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "N-iris-pseudacorus"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-flag-iris-2"
    },
    {
      "label": "People",
      "sources": [
        "N-iris-pseudacorus"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-flag-iris-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [
        "N-iris-pseudacorus"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-flag-iris-4"
    },
    {
      "label": "Other animals",
      "sources": [
        "N-iris-pseudacorus"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "yellow-flag-iris-5"
    },
    {
      "id": "yellow-flag-iris-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": "A",
  "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": "Expert review",
        "question": "Obtain independent botanical and veterinary review of the identification and hazard summary.",
        "related_claim_ids": []
      }
    ],
    "expert_review": "pending"
  },
  "noxious_class_label": "A — Eradicate",
  "source": "content/plants/yellow-flag-iris.md"
}
---

# Yellow flag iris

*Iris pseudacorus*

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

Uncommon in Colorado. All populations are designated for eradication statewide. 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).

> **Ingestion concern; invasive wetland colonies.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

## Still researching this plant {#research-status}

This is a sourced working profile. The cited findings are available 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.

![Iris pseudacorus: A yellow iris flower with dark markings on the large drooping segment.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-a-photos-iris-pseudacorus-1.jpg)

**flower detail** — A yellow iris flower with dark markings on the large drooping segment.

Photo: Kailey Alderfer; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/164186914); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/284056692/original.jpeg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. iNaturalist large server-resized image; no local crop, colour change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Iris pseudacorus: A yellow flower held among long sword-shaped leaves.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-a-photos-iris-pseudacorus-2.jpg)

**flower and leaves** — A yellow flower held among long sword-shaped leaves.

Photo: Kailey Alderfer; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/164186914); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/284056715/original.jpeg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. iNaturalist large server-resized image; no local crop, colour change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Iris pseudacorus: A flowering clump of yellow iris and upright sword-shaped leaves beside water.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-a-photos-iris-pseudacorus-3.jpg)

**habit** — A flowering clump of yellow iris and upright sword-shaped leaves beside water.

Photo: Kailey Alderfer; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/164186914); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/284056756/original.jpeg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. iNaturalist large server-resized image; no local crop, colour change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.


## Recognize

Yellow iris flowers rise among upright, sword-shaped leaves along wet ground or shallow water. [N-iris-pseudacorus](https://plants.ces.ncsu.edu/plants/iris-pseudacorus/)

## Plants & habitat

Seeds and rhizomes can create dense colonies that displace wetland plants. [N-iris-pseudacorus](https://plants.ces.ncsu.edu/plants/iris-pseudacorus/)

## People

Ingestion can cause gastrointestinal symptoms. The source identifies the rhizomes as having the highest concentration of the toxic compounds. [N-iris-pseudacorus](https://plants.ces.ncsu.edu/plants/iris-pseudacorus/)

## Dogs & cats

NC State flags both dogs and cats; prevent chewing or digging up rhizomes and obtain veterinary advice after ingestion. [N-iris-pseudacorus](https://plants.ces.ncsu.edu/plants/iris-pseudacorus/)

## Other animals

The source also flags horses, without establishing a safe feeding amount. [N-iris-pseudacorus](https://plants.ces.ncsu.edu/plants/iris-pseudacorus/)

## 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/)

This is a statewide eradication priority. Contact your county weed program promptly for identification and an approved management and disposal plan. [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2)

## 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.
- **N-iris-pseudacorus** — [iris pseudacorus — Plant Toolbox](https://plants.ces.ncsu.edu/plants/iris-pseudacorus/), NC State Extension. Accessed 2026-09-07T01:04:53+00:00. Locator: Description; Attributes; Problems; Poisonous to Humans.
- **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=yellow-flag-iris) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

# Appendix for agents

## Open research questions

- **Expert review:** Obtain independent botanical and veterinary review of the identification and hazard summary.


## Identity and evidence boundaries

Match the scientific name and synonyms, not the common name alone.

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 |
|---|---|---|---|---|
| yellow-flag-iris-1 | Recognize | Species-specific | N-iris-pseudacorus | No quantitative safe exposure established here. |
| yellow-flag-iris-2 | Plants & habitat | Species-specific | N-iris-pseudacorus | No quantitative safe exposure established here. |
| yellow-flag-iris-3 | People | Species-specific | N-iris-pseudacorus | No quantitative safe exposure established here. |
| yellow-flag-iris-4 | Dogs & cats | Species-specific | N-iris-pseudacorus | No quantitative safe exposure established here. |
| yellow-flag-iris-5 | Other animals | Species-specific | N-iris-pseudacorus | 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 “A — Eradicate” 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-flag-iris/

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

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

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