---
{
  "id": "western-poison-ivy",
  "name": "Western poison ivy",
  "scientific": "Toxicodendron rydbergii",
  "category": "native",
  "status": "Colorado native; contact hazard",
  "status_sources": [
    "C-wetland-guide"
  ],
  "warning": "Skin-rash oil can travel on pet fur",
  "warning_tone": "danger",
  "aliases": [
    "Rydberg’s poison ivy"
  ],
  "taxonomy_note": "The FDA advice covers poison ivy as a group. Source identification distinguishes this western species from other Toxicodendron taxa.",
  "source_ids": [
    "C-wetland-guide",
    "FDA-poison-ivy",
    "S27"
  ],
  "description": "Western poison ivy: Skin-rash oil can travel on pet fur. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "C-wetland-guide"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "western-poison-ivy-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "C-wetland-guide"
      ],
      "scope": "Ecology plus site-management inference",
      "note": "",
      "id": "western-poison-ivy-2"
    },
    {
      "label": "People",
      "sources": [
        "FDA-poison-ivy"
      ],
      "scope": "Poison-ivy group evidence",
      "note": "",
      "id": "western-poison-ivy-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [
        "FDA-poison-ivy"
      ],
      "scope": "Poison-ivy group evidence",
      "note": "",
      "id": "western-poison-ivy-4"
    },
    {
      "label": "Other animals",
      "sources": [
        "C-wetland-guide"
      ],
      "scope": "Ecological observation, not feed clearance",
      "note": "",
      "id": "western-poison-ivy-5"
    }
  ],
  "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": "Other animals",
        "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.",
        "related_claim_ids": [
          "western-poison-ivy-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"
  },
  "source": "content/plants/western-poison-ivy.md"
}
---

# Western poison ivy

*Toxicodendron rydbergii*

**Colorado native; contact hazard.** [C-wetland-guide](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf)

> **Skin-rash oil can travel on pet fur.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** The FDA advice covers poison ivy as a group. Source identification distinguishes this western species from other Toxicodendron taxa.

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

This is a sourced working profile. Evidence is incomplete for **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.

![Toxicodendron rydbergii: Dense cluster of pale whitish berries among dry leaves and twigs.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-toxicodendron-rydbergii-18-01-fruit.jpg)

**fruit** — Dense cluster of pale whitish berries among dry leaves and twigs.

Photo: Andrey Zharkikh from Salt Lake City, USA; [CC BY 2.0](https://creativecommons.org/licenses/by/2.0); [source record](https://commons.wikimedia.org/wiki/File:2009.09.24_18.43.13_CIMG2618_(6678712231).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/e/ec/2009.09.24_18.43.13_CIMG2618_%286678712231%29.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. Western poison ivy is treated differently in some floras, including within the T. radicans complex. Images are source-identified T. rydbergii; a three-leaflet leaf by itself is not species-specific. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Toxicodendron rydbergii: Branching clusters of tiny pale yellow-green flowers beside young stems.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-toxicodendron-rydbergii-18-08-flower.jpg)

**flower** — Branching clusters of tiny pale yellow-green flowers beside young stems.

Photo: Robert Flogaus-Faust; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0); [source record](https://commons.wikimedia.org/wiki/File:Toxicodendron_rydbergii_2_RF.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/d/d6/Toxicodendron_rydbergii_2_RF.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. Western poison ivy is treated differently in some floras, including within the T. radicans complex. Images are source-identified T. rydbergii; a three-leaflet leaf by itself is not species-specific. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Toxicodendron rydbergii: Low patch of woody shoots bearing groups of three broad green leaflets.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-toxicodendron-rydbergii-18-10-habit-foliage.jpg)

**habit-foliage** — Low patch of woody shoots bearing groups of three broad green leaflets.

Photo: Robert Flogaus-Faust; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0); [source record](https://commons.wikimedia.org/wiki/File:Toxicodendron_rydbergii_RF.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/1/14/Toxicodendron_rydbergii_RF.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. Western poison ivy is treated differently in some floras, including within the T. radicans complex. Images are source-identified T. rydbergii; a three-leaflet leaf by itself is not species-specific. 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

A low shrub with leaves divided into three leaflets and pale fruits. Colorado’s regional flora identifies this native species. [C-wetland-guide](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf)

## Plants & habitat

Spreads through underground growth. Its native ecological role does not remove the need to manage contact near paths and play areas. [C-wetland-guide](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf)

*Evidence scope: Ecology plus site-management inference.*

## People

Urushiol oil can cause an itchy rash and remain on tools or clothing. Smoke from burning poison ivy is hazardous; do not burn it. [FDA-poison-ivy](https://www.fda.gov/consumers/consumer-updates/outsmarting-poison-ivy-and-other-poisonous-plants)

*Evidence scope: Poison-ivy group evidence.*

## Dogs & cats

Most pets are less sensitive to the oil, but fur can carry it to people. Avoid barehanded contact with exposed fur and get advice on safe cleaning. [FDA-poison-ivy](https://www.fda.gov/consumers/consumer-updates/outsmarting-poison-ivy-and-other-poisonous-plants)

*Evidence scope: Poison-ivy group evidence.*

## Other animals

The Colorado flora describes wildlife browsing. This does not establish safe feed quantities for livestock or pets. [C-wetland-guide](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf)

*Evidence scope: Ecological observation, not feed clearance.*

## 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-wetland-guide** — [Common Wetland Plants of Colorado’s Western Slope](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf), Colorado Natural Heritage Program / Colorado State University. Accessed 2026-09-07T01:14:13+00:00. Locator: Water hemlock and western poison ivy entries; taxonomic scope.
- **FDA-poison-ivy** — [Outsmarting Poison Ivy and Other Poisonous Plants](https://www.fda.gov/consumers/consumer-updates/outsmarting-poison-ivy-and-other-poisonous-plants), US Food and Drug Administration. Accessed 2026-09-07T01:16:19+00:00. Locator: Species identity, description, ecological and exposure evidence; verify group scope.
- **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=western-poison-ivy) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

# Appendix for agents

## Open research questions

- **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

The FDA advice covers poison ivy as a group. Source identification distinguishes this western species from other Toxicodendron taxa.

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 |
|---|---|---|---|---|
| western-poison-ivy-1 | Recognize | Species-specific | C-wetland-guide | No quantitative safe exposure established here. |
| western-poison-ivy-2 | Plants & habitat | Ecology plus site-management inference | C-wetland-guide | No quantitative safe exposure established here. |
| western-poison-ivy-3 | People | Poison-ivy group evidence | FDA-poison-ivy | No quantitative safe exposure established here. |
| western-poison-ivy-4 | Dogs & cats | Poison-ivy group evidence | FDA-poison-ivy | No quantitative safe exposure established here. |
| western-poison-ivy-5 | Other animals | Ecological observation, not feed clearance | C-wetland-guide | 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/western-poison-ivy/

Content revised: 2026-09-07T02:43:00Z

Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/western-poison-ivy/index.md

Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/western-poison-ivy/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