---
{
  "id": "hybrid-knapweed",
  "name": "Spotted × diffuse knapweed hybrid",
  "scientific": "Centaurea × psammogena",
  "category": "invasive",
  "status": "Colorado noxious weed · List B — Stop the spread",
  "status_sources": [
    "CO-rules-2025"
  ],
  "warning": "Hybrid identification needs expert review",
  "warning_tone": "caution",
  "aliases": [
    "hybrid knapweed"
  ],
  "taxonomy_note": "The source explains chromosome and subspecies differences in the parents and uncertainty in older identifications. The photographs come from a community research-grade Colorado observation, not genetic testing. No parent-species poisoning syndrome is assumed for the hybrid.",
  "source_ids": [
    "CO-rules-2025",
    "F-knapweed",
    "S27",
    "Fremont-list-definitions"
  ],
  "description": "Spotted × diffuse knapweed hybrid: Hybrid identification needs expert review. Identification and evidence for Colorado readers.",
  "claim_evidence": [
    {
      "label": "Recognize",
      "sources": [
        "F-knapweed"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "hybrid-knapweed-1"
    },
    {
      "label": "Plants & habitat",
      "sources": [
        "F-knapweed",
        "CO-rules-2025"
      ],
      "scope": "Species-specific",
      "note": "",
      "id": "hybrid-knapweed-2"
    },
    {
      "label": "People",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "hybrid-knapweed-3"
    },
    {
      "label": "Dogs & cats",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "hybrid-knapweed-4"
    },
    {
      "label": "Other animals",
      "sources": [],
      "scope": "Review limitation",
      "note": "",
      "id": "hybrid-knapweed-5"
    },
    {
      "id": "hybrid-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": [
          "hybrid-knapweed-3"
        ]
      },
      {
        "area": "Dogs & cats",
        "question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
        "related_claim_ids": [
          "hybrid-knapweed-4"
        ]
      },
      {
        "area": "Other animals",
        "question": "Clarify feeding and exposure risks for each animal group; do not transfer findings between species.",
        "related_claim_ids": [
          "hybrid-knapweed-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": "B — Stop the spread",
  "source": "content/plants/hybrid-knapweed.md"
}
---

# Spotted × diffuse knapweed hybrid

*Centaurea × psammogena*

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

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).

> **Hybrid identification needs expert review.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).

**Identification caveat:** The source explains chromosome and subspecies differences in the parents and uncertainty in older identifications. The photographs come from a community research-grade Colorado observation, not genetic testing. No parent-species poisoning syndrome is assumed for the hybrid.

## 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.

![A pink-purple hybrid-knapweed head and several buds held beside branching stems; the source identifies this Littleton, Colorado plant as Centaurea × psammogena.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-centaurea-x-psammogena-inat-409969172.jpg)

**head and bracts** — A pink-purple hybrid-knapweed head and several buds held beside branching stems; the source identifies this Littleton, Colorado plant as Centaurea × psammogena.

Photo: Tyler; [CC0 1.0](https://creativecommons.org/publicdomain/zero/1.0/); [source record](https://www.inaturalist.org/observations/230868147); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/409969172/original.jpeg). Explicit research-grade community taxon identification; visually inspected Community identification is explicit; hybrid status has not been independently confirmed genetically. iNaturalist large-size rendering; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![A widely branched hybrid-knapweed plant with scattered pink-purple heads in dry vegetation; source location is Littleton, Colorado.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-centaurea-x-psammogena-inat-409969216.jpg)

**habit** — A widely branched hybrid-knapweed plant with scattered pink-purple heads in dry vegetation; source location is Littleton, Colorado.

Photo: Tyler; [CC0 1.0](https://creativecommons.org/publicdomain/zero/1.0/); [source record](https://www.inaturalist.org/observations/230868147); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/409969216/original.jpeg). Explicit research-grade community taxon identification; visually inspected Community identification is explicit; hybrid status has not been independently confirmed genetically. iNaturalist large-size rendering; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.

![Close view of a pale pink and purple hybrid-knapweed flower head; source location is Littleton, Colorado.](https://denson.github.io/colorado-weed-field-guide/assets/photos/list-bc-photos-centaurea-x-psammogena-inat-409969094.jpg)

**flower** — Close view of a pale pink and purple hybrid-knapweed flower head; source location is Littleton, Colorado.

Photo: Tyler; [CC0 1.0](https://creativecommons.org/publicdomain/zero/1.0/); [source record](https://www.inaturalist.org/observations/230868147); [original image](https://inaturalist-open-data.s3.amazonaws.com/photos/409969094/original.jpeg). Explicit research-grade community taxon identification; visually inspected Community identification is explicit; hybrid status has not been independently confirmed genetically. iNaturalist large-size rendering; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.


## Recognize

A fertile hybrid of diffuse and spotted knapweed, often misidentified. A mix of parental appearance does not by itself prove hybrid identity. [F-knapweed](https://research.fs.usda.gov/feis/species-reviews/cendif)

## Plants & habitat

The Forest Service records the hybrid in Colorado. Colorado lists the hybrid separately, so do not discard suspect plants from a weed survey simply because they do not fit a parent’s key. [F-knapweed](https://research.fs.usda.gov/feis/species-reviews/cendif) [CO-rules-2025](https://www.sos.state.co.us/CCR/GenerateRulePdf.do?ruleVersionId=11948&fileName=8+CCR+1206-2)

## 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/)

## 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.
- **F-knapweed** — [Diffuse knapweed and hybrid taxonomy](https://research.fs.usda.gov/feis/species-reviews/cendif), USDA Forest Service Fire Effects Information System. Accessed 2026-09-07T01:21:11+00:00. Locator: Species identity, description, ecology and exposure evidence.
- **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=hybrid-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.
- **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 source explains chromosome and subspecies differences in the parents and uncertainty in older identifications. The photographs come from a community research-grade Colorado observation, not genetic testing. No parent-species poisoning syndrome is assumed for the hybrid.

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 |
|---|---|---|---|---|
| hybrid-knapweed-1 | Recognize | Species-specific | F-knapweed | No quantitative safe exposure established here. |
| hybrid-knapweed-2 | Plants & habitat | Species-specific | F-knapweed, CO-rules-2025 | No quantitative safe exposure established here. |
| hybrid-knapweed-3 | People | Review limitation | Review limitation | No quantitative safe exposure established here. |
| hybrid-knapweed-4 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. |
| hybrid-knapweed-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 “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/hybrid-knapweed/

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

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

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