---
{
"id": "mayweed-chamomile",
"name": "Mayweed chamomile",
"scientific": "Anthemis cotula",
"category": "invasive",
"status": "Colorado noxious weed · List B — Stop the spread",
"status_sources": [
"CO-rules-2025"
],
"warning": "Crop weed with unpleasant-smelling foliage",
"warning_tone": "caution",
"aliases": [
"stinking chamomile",
"dog fennel"
],
"taxonomy_note": "Do not substitute Roman chamomile (Anthemis nobilis / Chamaemelum nobile) toxicology. The retrieved NC State URL described a different plant and was excluded.",
"source_ids": [
"CO-rules-2025",
"UC-mayweed",
"K-chamomiles",
"S27",
"Fremont-list-definitions"
],
"description": "Mayweed chamomile: Crop weed with unpleasant-smelling foliage. Identification and evidence for Colorado readers.",
"claim_evidence": [
{
"label": "Recognize",
"sources": [
"UC-mayweed"
],
"scope": "Species-specific",
"note": "",
"id": "mayweed-chamomile-1"
},
{
"label": "Plants & habitat",
"sources": [
"UC-mayweed"
],
"scope": "Species-specific",
"note": "",
"id": "mayweed-chamomile-2"
},
{
"label": "People",
"sources": [],
"scope": "Review limitation",
"note": "",
"id": "mayweed-chamomile-3"
},
{
"label": "Dogs & cats",
"sources": [],
"scope": "Review limitation",
"note": "",
"id": "mayweed-chamomile-4"
},
{
"label": "Other animals",
"sources": [
"K-chamomiles"
],
"scope": "Species-specific",
"note": "",
"id": "mayweed-chamomile-5"
},
{
"id": "mayweed-chamomile-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": [
"mayweed-chamomile-3"
]
},
{
"area": "Dogs & cats",
"question": "Find species-specific dog and cat exposure evidence; do not infer safety from missing reports.",
"related_claim_ids": [
"mayweed-chamomile-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"
},
"noxious_class_label": "B — Stop the spread",
"source": "content/plants/mayweed-chamomile.md"
}
---
# Mayweed chamomile
*Anthemis cotula*
**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).
> **Crop weed with unpleasant-smelling foliage.** [Exposure help](https://denson.github.io/colorado-weed-field-guide/safety/).
**Identification caveat:** Do not substitute Roman chamomile (Anthemis nobilis / Chamaemelum nobile) toxicology. The retrieved NC State URL described a different plant and was excluded.
## Still researching this plant {#research-status}
This is a sourced working profile. Evidence is incomplete for **People, 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.
**flowers** — Mayweed chamomile heads with white rays around raised yellow centers.
Photo: NY State IPM Program at Cornell University from New York, USA; [CC BY 2.0](https://creativecommons.org/licenses/by/2.0); [source record](https://commons.wikimedia.org/wiki/File:Anthemis_cotula_-_flowers_(closeup)_(18744849431).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/1/13/Anthemis_cotula_-_flowers_%28closeup%29_%2818744849431%29.jpg). Source-identified photograph with visual consistency check Mayweed chamomile. For more information on identification and control, visit turfweeds.cals.cornell.edu/plant/identify/157 Source labeling and visible consistency checked; not an independent specimen determination. Wikimedia-generated thumbnail rescaling only; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.
**habit** — A broad, branching mayweed chamomile plant covered with numerous small white-and-yellow flower heads.
Photo: NY State IPM Program at Cornell University from New York, USA; [CC BY 2.0](https://creativecommons.org/licenses/by/2.0); [source record](https://commons.wikimedia.org/wiki/File:Anthemis_cotula_-_whole_plant_(18737495852).jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/0/09/Anthemis_cotula_-_whole_plant_%2818737495852%29.jpg). Source-identified photograph with visual consistency check Mayweed chamomile. For more information on identification and control, visit turfweeds.cals.cornell.edu/plant/identify/157 Source labeling and visible consistency checked; not an independent specimen determination. Wikimedia-generated thumbnail rescaling only; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.
**foliage** — A leafy mayweed chamomile shoot with finely divided green foliage.
Photo: Andrianl; [CC0](http://creativecommons.org/publicdomain/zero/1.0/deed.en); [source record](https://commons.wikimedia.org/wiki/File:Anthemis_cotula_592189591.jpg); [original image](https://upload.wikimedia.org/wikipedia/commons/d/d1/Anthemis_cotula_592189591.jpg). Source-identified photograph with visual consistency check Stinking chamomile ( Anthemis cotula ) in New Zealand Source labeling and visible consistency checked; not an independent specimen determination. Wikimedia-generated thumbnail rescaling only; downloaded bytes unchanged. Gallery display preserves the full image; the catalog preview uses a CSS crop.
## Recognize
A bushy annual with finely divided leaves, white ray flowers around yellow centers and a strong, unpleasant odor. [UC-mayweed](https://ipm.ucanr.edu/weeds-identification-gallery/mayweed-chamomile/)
## Plants & habitat
Colonizes disturbed ground and agricultural sites; seed production sustains infestations. [UC-mayweed](https://ipm.ucanr.edu/weeds-identification-gallery/mayweed-chamomile/)
## 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
Cornell reports livestock avoidance and milk taint after consumption. That is not a quantified pet-poisoning assessment. [K-chamomiles](https://cals.cornell.edu/weed-science/weed-profiles/chamomiles)
## 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.
- **UC-mayweed** — [Mayweed chamomile](https://ipm.ucanr.edu/weeds-identification-gallery/mayweed-chamomile/), University of California Statewide IPM. Accessed 2026-09-07T01:16:19+00:00. Locator: Species identity, description, ecological and exposure evidence; verify group scope.
- **K-chamomiles** — [Chamomiles](https://cals.cornell.edu/weed-science/weed-profiles/chamomiles), Cornell University College of Agriculture and Life Sciences. 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=mayweed-chamomile) — 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.
- **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
Do not substitute Roman chamomile (Anthemis nobilis / Chamaemelum nobile) toxicology. The retrieved NC State URL described a different plant and was 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 |
|---|---|---|---|---|
| mayweed-chamomile-1 | Recognize | Species-specific | UC-mayweed | No quantitative safe exposure established here. |
| mayweed-chamomile-2 | Plants & habitat | Species-specific | UC-mayweed | No quantitative safe exposure established here. |
| mayweed-chamomile-3 | People | Review limitation | Review limitation | No quantitative safe exposure established here. |
| mayweed-chamomile-4 | Dogs & cats | Review limitation | Review limitation | No quantitative safe exposure established here. |
| mayweed-chamomile-5 | Other animals | Species-specific | K-chamomiles | 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/mayweed-chamomile/
Content revised: 2026-09-07T03:50:00Z
Markdown mirror: https://denson.github.io/colorado-weed-field-guide/plants/mayweed-chamomile/index.md
Text fallback: https://denson.github.io/colorado-weed-field-guide/plants/mayweed-chamomile/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