---
{
  "id": "russian-knapweed",
  "name": "Russian knapweed",
  "scientific": "Rhaponticum repens",
  "category": "invasive",
  "status": "Colorado noxious weed · List B — Stop the spread",
  "status_sources": [
    "J-russian-knapweed"
  ],
  "warning": "Toxic to horses",
  "warning_tone": "danger",
  "aliases": [
    "Acroptilon repens",
    "Centaurea repens"
  ],
  "taxonomy_note": "The county page misspells the old genus as Arcoptilon; Acroptilon repens is the synonym used by NC State.",
  "source_ids": [
    "J-russian-knapweed",
    "N-rhaponticum-repens",
    "Fremont-list-definitions"
  ],
  "description": "Russian knapweed: Toxic to horses. Colorado identification, habitat and exposure evidence.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "J-russian-knapweed"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "russian-knapweed-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "N-rhaponticum-repens",
        "J-russian-knapweed"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "russian-knapweed-2"
    },
    {
      "label": "People",
      "sources": [],
      "scope": "Review limitation",
      "note": "Human ingestion effects were not established in this review.",
      "id": "russian-knapweed-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [
        "N-rhaponticum-repens"
      ],
      "scope": "Source tag; evidence detail limited",
      "note": "",
      "id": "russian-knapweed-4"
    },
    {
      "label": "Other animals",
      "sources": [
        "N-rhaponticum-repens"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "russian-knapweed-5"
    },
    {
      "id": "russian-knapweed-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": [
          "russian-knapweed-3"
        ]
      },
      {
        "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/russian-knapweed.md"
}
---

# Russian knapweed

*Rhaponticum repens*

**Colorado noxious weed · List B — Stop the spread.** [J-russian-knapweed](https://www.jeffco.us/4107/Russian-knapweed)

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).

> **Toxic to horses.** 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:** The county page misspells the old genus as Arcoptilon; Acroptilon repens is the synonym used by NC State.

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

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

![Rhaponticum repens: Dense patch of upright gray-green leafy plants beneath trees.](https://denson.github.io/colorado-weed-field-guide/assets/photos/invasive-rhaponticum-repens-habit.jpg)

**habit** — Dense patch of upright gray-green leafy plants beneath trees.

Photo: Amirh. absnd; [CC0](https://creativecommons.org/publicdomain/zero/1.0/deed.en); [source record](https://commons.wikimedia.org/wiki/File:Acroptilon_repens_absnd.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/3/32/Acroptilon_repens_absnd.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.  Source names Acroptilon repens and Rhaponticum repens are treated here as synonyms for Russian knapweed. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Rhaponticum repens: Upright dry stems with pale tan mature heads and yellowing leaves.](https://denson.github.io/colorado-weed-field-guide/assets/photos/invasive-rhaponticum-repens-mature-head.jpg)

**mature-head** — Upright dry stems with pale tan mature heads and yellowing leaves.

Photo: Matt Lavin from Bozeman, Montana, USA; [CC BY-SA 2.0](https://creativecommons.org/licenses/by-sa/2.0); [source record](https://commons.wikimedia.org/wiki/File:Rhaponticum_repens_(5042408076).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/0/04/Rhaponticum_repens_%285042408076%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.  Source names Acroptilon repens and Rhaponticum repens are treated here as synonyms for Russian knapweed. Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Rhaponticum repens: Purple flower head above overlapping pale papery-tipped bracts, with narrow upper leaves.](https://denson.github.io/colorado-weed-field-guide/assets/photos/invasive-rhaponticum-repens-flower.jpg)

**flower** — Purple flower head above overlapping pale papery-tipped bracts, with narrow upper leaves.

Photo: Stan Shebs; [CC BY-SA 3.0](https://creativecommons.org/licenses/by-sa/3.0); [source record](https://commons.wikimedia.org/wiki/File:Rhaponticum_repens_4.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/7/7f/Rhaponticum_repens_4.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.  Source names Acroptilon repens and Rhaponticum repens are treated here as synonyms for Russian knapweed. 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

Pink to lavender heads with tan, papery bracts; creeping dark roots beneath a perennial stand. [J-russian-knapweed](https://www.jeffco.us/4107/Russian-knapweed)

## Plants & habitat

Spreading roots produce persistent colonies that displace native vegetation. Cutting alone does not resolve the deep root system. [N-rhaponticum-repens](https://plants.ces.ncsu.edu/plants/rhaponticum-repens/) [J-russian-knapweed](https://www.jeffco.us/4107/Russian-knapweed)

## People

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

## Dogs & cats

NC State tags the plant non-toxic to dogs and cats but provides no supporting pet assessment in its main text. We retain that limited claim without treating it as a safety clearance. [N-rhaponticum-repens](https://plants.ces.ncsu.edu/plants/rhaponticum-repens/)

## Other animals

Poisonous to horses. Keep it out of horse pasture and hay and contact a veterinarian after suspected ingestion. [N-rhaponticum-repens](https://plants.ces.ncsu.edu/plants/rhaponticum-repens/)

## 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-russian-knapweed** — [Russian knapweed](https://www.jeffco.us/4107/Russian-knapweed), Jefferson County, Colorado. Accessed 2026-09-07T00:27:24+00:00. Locator: Description, impacts, Colorado list designation, management.
- **N-rhaponticum-repens** — [Rhaponticum repens — Plant Toolbox](https://plants.ces.ncsu.edu/plants/rhaponticum-repens/), NC State Extension. Accessed 2026-09-07T00:24:01+00:00. Locator: Description, Attributes, Poisonous to Humans, Problems.


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

The county page misspells the old genus as Arcoptilon; Acroptilon repens is the synonym used by NC State.

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 |
|---|---|---|---|---|
| russian-knapweed-1 | Recognize | Species-specific | J-russian-knapweed | No quantitative exposure threshold established here. |
| russian-knapweed-2 | Plants & habitat | Species-specific | N-rhaponticum-repens, J-russian-knapweed | No quantitative exposure threshold established here. |
| russian-knapweed-3 | People | Review limitation | Review limitation | Human ingestion effects were not established in this review. |
| russian-knapweed-4 | Dogs & cats | Source tag; evidence detail limited | N-rhaponticum-repens | No quantitative exposure threshold established here. |
| russian-knapweed-5 | Other animals | Species-specific | N-rhaponticum-repens | 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/russian-knapweed/

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

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

Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/russian-knapweed/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