---
{
  "id": "western-water-hemlock",
  "name": "Western water hemlock",
  "scientific": "Cicuta douglasii",
  "category": "native",
  "status": "Native wetland hazard; not an A/B/C listing in the reviewed rule",
  "status_sources": [
    "C-wetland-guide",
    "CO-rules-2025"
  ],
  "warning": "Potentially fatal poisoning; wetland look-alike danger",
  "warning_tone": "danger",
  "aliases": [],
  "taxonomy_note": "The older Colorado wetland guide treats C. douglasii within C. maculata var. angustifolia. The photos and Utah source identify C. douglasii. This is separate from poison hemlock (Conium maculatum). Older home-treatment instructions and an incorrect chemical classification in sources are excluded.",
  "source_ids": [
    "C-wetland-guide",
    "CO-rules-2025",
    "U-water-hemlock",
    "C-routt-guide",
    "S27"
  ],
  "description": "Western water hemlock: Potentially fatal poisoning; wetland look-alike danger. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "U-water-hemlock"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "western-water-hemlock-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "C-wetland-guide"
      ],
      "scope": "Older regional flora; taxonomic scope differs",
      "note": "",
      "id": "western-water-hemlock-2"
    },
    {
      "label": "People",
      "sources": [
        "C-routt-guide"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "western-water-hemlock-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [
        "C-routt-guide"
      ],
      "scope": "Dog warning; cat evidence gap",
      "note": "",
      "id": "western-water-hemlock-4"
    },
    {
      "label": "Other animals",
      "sources": [
        "U-water-hemlock"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "western-water-hemlock-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": "Dogs & cats",
        "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
        "related_claim_ids": [
          "western-water-hemlock-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"
  },
  "source": "content/plants/western-water-hemlock.md"
}
---

# Western water hemlock

*Cicuta douglasii*

**Native wetland hazard; not an A/B/C listing in the reviewed rule.** [C-wetland-guide](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf) [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2)

> **Potentially fatal poisoning; wetland look-alike danger.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** The older Colorado wetland guide treats C. douglasii within C. maculata var. angustifolia. The photos and Utah source identify C. douglasii. This is separate from poison hemlock (Conium maculatum). Older home-treatment instructions and an incorrect chemical classification in sources are excluded.

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

This is a sourced working profile. Evidence is incomplete for **Dogs & cats**. 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.

![Cicuta douglasii: Upright leafy stems with pinnately divided, sharply toothed leaflets.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-cicuta-douglasii-17-04-habit.jpg)

**habit** — Upright leafy stems with pinnately divided, sharply toothed leaflets.

Photo: Lee Cain; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0); [source record](https://commons.wikimedia.org/wiki/File:Cicuta_douglasii_284166253.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/1/18/Cicuta_douglasii_284166253.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. Water-hemlock species are difficult to distinguish in general photographs. These references are explicitly source-identified C. douglasii; they are not proof that an unknown water-hemlock belongs to this species. C. maculata and related taxa require a regional botanical key and reproductive details. Comparison images also showing Conium were excluded. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Cicuta douglasii: Rounded clusters of pale flowers and developing fruits form a compound umbel.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-cicuta-douglasii-17-06-flower.jpg)

**flower** — Rounded clusters of pale flowers and developing fruits form a compound umbel.

Photo: Matt Berger; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0); [source record](https://commons.wikimedia.org/wiki/File:Cicuta_douglasii_442485760.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/e/eb/Cicuta_douglasii_442485760.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. Water-hemlock species are difficult to distinguish in general photographs. These references are explicitly source-identified C. douglasii; they are not proof that an unknown water-hemlock belongs to this species. C. maculata and related taxa require a regional botanical key and reproductive details. Comparison images also showing Conium were excluded. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Cicuta douglasii: Pinnately arranged lance-shaped leaflets with sharply toothed margins and visible side veins.](https://denson.github.io/colorado-weed-field-guide/assets/photos/common-priority-photos-cicuta-douglasii-17-07-leaf.jpg)

**leaf** — Pinnately arranged lance-shaped leaflets with sharply toothed margins and visible side veins.

Photo: N5jrn; [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0); [source record](https://commons.wikimedia.org/wiki/File:Cicuta_douglasii_leaf_detail.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/c/c7/Cicuta_douglasii_leaf_detail.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. Water-hemlock species are difficult to distinguish in general photographs. These references are explicitly source-identified C. douglasii; they are not proof that an unknown water-hemlock belongs to this species. C. maculata and related taxa require a regional botanical key and reproductive details. Comparison images also showing Conium were excluded. 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 wetland perennial with clusters of small white flowers and divided leaves; veins terminate in notches between the leaflet teeth. Never taste, cut roots or use this short description as a foraging test. [U-water-hemlock](https://extension.usu.edu/rangeplants/forbs-herbaceous/water-hemlock)

## Plants & habitat

Occurs around wet ground, ditches and waterways. Colorado floras have used broader Cicuta names for related populations. [C-wetland-guide](https://cnhp.colostate.edu/wp-content/uploads/download/documents/cwic_docs/WesternSlope.pdf)

*Evidence scope: Older regional flora; taxonomic scope differs.*

## People

Routt County identifies water hemlock as a potentially lethal poison. Treat suspected ingestion as an emergency. [C-routt-guide](https://routt.extension.colostate.edu/wp-content/uploads/sites/4/2021/06/RC_Weed_Guide_2021.pdf)

## Dogs & cats

The county guide explicitly warns about dogs. Cat-specific clinical detail is not established here; keep all pets away from chewing plants or exposed roots. [C-routt-guide](https://routt.extension.colostate.edu/wp-content/uploads/sites/4/2021/06/RC_Weed_Guide_2021.pdf)

*Evidence scope: Dog warning; cat evidence gap.*

## Other animals

Highly poisonous to livestock, especially the roots. Convulsions and death can follow ingestion. [U-water-hemlock](https://extension.usu.edu/rangeplants/forbs-herbaceous/water-hemlock)

## 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.
- **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-water-hemlock** — [Water Hemlock](https://extension.usu.edu/rangeplants/forbs-herbaceous/water-hemlock), Utah State University Extension. Accessed 2026-09-07T01:14:00+00:00. Locator: Cicuta douglasii identification and toxicity.
- **C-routt-guide** — [Routt County Weed Identification Guide](https://routt.extension.colostate.edu/wp-content/uploads/sites/4/2021/06/RC_Weed_Guide_2021.pdf), Routt County / Colorado State University Extension. Accessed 2026-09-07T01:14:14+00:00. Locator: Common weeds and poisonous plants; 2021 edition.
- **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-water-hemlock) — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

# Appendix for agents

## Open research questions

- **Dogs & cats:** Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.
- **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 older Colorado wetland guide treats C. douglasii within C. maculata var. angustifolia. The photos and Utah source identify C. douglasii. This is separate from poison hemlock (Conium maculatum). Older home-treatment instructions and an incorrect chemical classification in sources are excluded.

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-water-hemlock-1 | Recognize | Species-specific | U-water-hemlock | No quantitative safe exposure established here. |
| western-water-hemlock-2 | Plants & habitat | Older regional flora; taxonomic scope differs | C-wetland-guide | No quantitative safe exposure established here. |
| western-water-hemlock-3 | People | Species-specific | C-routt-guide | No quantitative safe exposure established here. |
| western-water-hemlock-4 | Dogs & cats | Dog warning; cat evidence gap | C-routt-guide | No quantitative safe exposure established here. |
| western-water-hemlock-5 | Other animals | Species-specific | U-water-hemlock | 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-water-hemlock/

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

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

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