---
{
  "id": "giant-knotweed",
  "name": "Giant knotweed",
  "scientific": "Reynoutria sachalinensis",
  "category": "invasive",
  "status": "Colorado noxious weed · List A — Eradicate",
  "status_sources": [
    "CO-rules-2025"
  ],
  "warning": "Very persistent riparian colonies",
  "warning_tone": "caution",
  "aliases": [
    "Fallopia sachalinense",
    "Fallopia sachalinensis",
    "Polygonum sachalinense"
  ],
  "taxonomy_note": "The state rule uses Fallopia sachalinense. Giant, Japanese and Bohemian knotweeds overlap in appearance; confirm identity beyond plant height.",
  "source_ids": [
    "CO-rules-2025",
    "WA-giant-knotweed",
    "S27",
    "Fremont-list-definitions"
  ],
  "description": "Giant knotweed: Very persistent riparian colonies. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "WA-giant-knotweed"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "giant-knotweed-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "WA-giant-knotweed"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "giant-knotweed-2"
    },
    {
      "label": "People",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "giant-knotweed-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "giant-knotweed-4"
    },
    {
      "label": "Other animals",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "giant-knotweed-5"
    },
    {
      "id": "giant-knotweed-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": "People",
        "question": "Clarify the human exposure effects and evidence limits described in this section.",
        "related_claim_ids": [
          "giant-knotweed-3"
        ]
      },
      {
        "area": "Dogs & cats",
        "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
        "related_claim_ids": [
          "giant-knotweed-4"
        ]
      },
      {
        "area": "Other animals",
        "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.",
        "related_claim_ids": [
          "giant-knotweed-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": "A — Eradicate",
  "source": "content/plants/giant-knotweed.md"
}
---

# Giant knotweed

*Reynoutria sachalinensis*

**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).

> **Very persistent riparian colonies.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** The state rule uses Fallopia sachalinense. Giant, Japanese and Bohemian knotweeds overlap in appearance; confirm identity beyond plant height.

## 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.

![Reynoutria sachalinensis: Upright shoots with broad, heart-based leaves among mixed ground vegetation.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-a-photos-reynoutria-sachalinensis-1.jpg)

**leafy shoots** — Upright shoots with broad, heart-based leaves among mixed ground vegetation.

Photo: Oleksandr Shynder; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/101817066); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/170078727/original.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Giant knotweed can be confused with Bohemian knotweed. Identification follows the research-grade source; leaf-base and magnified hair views are included, but photos alone do not establish hybrid ancestry. 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.

![Reynoutria sachalinensis: Broad leaves with visibly heart-shaped bases and prominent veins.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-a-photos-reynoutria-sachalinensis-2.jpg)

**leaf shape** — Broad leaves with visibly heart-shaped bases and prominent veins.

Photo: Oleksandr Shynder; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/101817066); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/170078917/original.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Giant knotweed can be confused with Bohemian knotweed. Identification follows the research-grade source; leaf-base and magnified hair views are included, but photos alone do not establish hybrid ancestry. 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.

![Reynoutria sachalinensis: Magnified leaf surface showing long, slender hairs near veins; the circular viewing field is part of the source photo.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-a-photos-reynoutria-sachalinensis-3.jpg)

**leaf hairs** — Magnified leaf surface showing long, slender hairs near veins; the circular viewing field is part of the source photo.

Photo: Oleksandr Shynder; [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/); [source record](https://www.inaturalist.org/observations/101817066); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/170079644/original.jpg). Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference image, not a specimen-based taxonomic determination. Giant knotweed can be confused with Bohemian knotweed. Identification follows the research-grade source; leaf-base and magnified hair views are included, but photos alone do not establish hybrid ancestry. 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

Very large, heart-based leaves on hollow, jointed stems; small greenish-white flower clusters arise near upper leaves. [WA-giant-knotweed](https://www.nwcb.wa.gov/weeds/giant-knotweed)

## Plants & habitat

Rhizomes form dense colonies and even small fragments can regenerate. Keep cut material and contaminated soil from spreading. [WA-giant-knotweed](https://www.nwcb.wa.gov/weeds/giant-knotweed)

## 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/)

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.
- **WA-giant-knotweed** — [Giant Knotweed](https://www.nwcb.wa.gov/weeds/giant-knotweed), Washington State Noxious Weed Control Board. Accessed 2026-09-07T01:09:00+00:00. Locator: Identification, ecological impacts, management; Washington legal class not applied to Colorado.
- **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=giant-knotweed) — 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

The state rule uses Fallopia sachalinense. Giant, Japanese and Bohemian knotweeds overlap in appearance; confirm identity beyond plant height.

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 |
|---|---|---|---|---|
| giant-knotweed-1 | Recognize | Species-specific | WA-giant-knotweed | No quantitative safe exposure established here. |
| giant-knotweed-2 | Plants & habitat | Species-specific | WA-giant-knotweed | No quantitative safe exposure established here. |
| giant-knotweed-3 | People | Review limitation | Review limitation | No quantitative safe exposure established here. |
| giant-knotweed-4 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. |
| giant-knotweed-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 “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/giant-knotweed/

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

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

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