Russian knapweed

Discuss this plant with the guide — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.

Rhaponticum repens

Colorado noxious weed · List B — Stop the spread. J-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 · What the lists mean.

Toxic to horses. Native status, garden use and noxious-weed class are separate from toxicity. Exposure help.

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

Still researching this plant

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. — **habit** — Dense patch of upright gray-green leafy plants beneath trees.
Amirh. absnd · CC0
Photo source and identification
Original record · Original image
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. — **mature-head** — Upright dry stems with pale tan mature heads and yellowing leaves.
Matt Lavin from Bozeman, Montana, USA · CC BY-SA 2.0
Photo source and identification
Original record · Original image
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. — **flower** — Purple flower head above overlapping pale papery-tipped bracts, with narrow upper leaves.
Stan Shebs · CC BY-SA 3.0
Photo source and identification
Original record · Original image
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

Plants & habitat

Spreading roots produce persistent colonies that displace native vegetation. Cutting alone does not resolve the deep root system. N-rhaponticum-repens J-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

Other animals

Poisonous to horses. Keep it out of horse pasture and hay and contact a veterinarian after suspected ingestion. N-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

References

J-russian-knapweed — 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, NC State Extension. Accessed 2026-09-07T00:24:01+00:00. Locator: Description, Attributes, Poisonous to Humans, Problems.

Content revised 2026-09-07 03:50:00Z · Source checks dated separately in the references.