Prickly sowthistle

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

Sonchus asper

Common introduced weed · not on state Lists A/B/C. C-floristic-2020 CO-rules-2025

Spiny leaves and rapid seed production. Exposure help.

Identification caveat: This is an annual Sonchus, not a true Cirsium thistle and not perennial sowthistle. Confirm leaf bases and life cycle.

Still researching this plant

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

Sonchus asper: A tall flowering prickly sow-thistle with lobed leaves beside a tree trunk. — **habit** — A tall flowering prickly sow-thistle with lobed leaves beside a tree trunk.
Didier Descouens · CC BY-SA 4.0
Photo source and identification
Original record · Original image
Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Source identification is retained. The rounded clasping leaf lobes and prickly leaf edges are shown for comparison with S. oleraceus; hybrids and other lookalikes require a full key.
Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop.

Sonchus asper: Glossy, spine-toothed leaves clasping the stem with rounded basal lobes. — **leaf attachment** — Glossy, spine-toothed leaves clasping the stem with rounded basal lobes.
Douglas Goldman · CC BY-SA 4.0
Photo source and identification
Original record · Original image
Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Source identification is retained. The rounded clasping leaf lobes and prickly leaf edges are shown for comparison with S. oleraceus; hybrids and other lookalikes require a full key.
iNaturalist large server-resized photo; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop.

Sonchus asper: A rounded white pappus head ready to release its fruits. — **seed head** — A rounded white pappus head ready to release its fruits.
Matt Lavin from Bozeman, Montana, USA · CC BY-SA 2.0
Photo source and identification
Original record · Original image
Source scientific identification plus visual morphology review of the selected photograph. This is a source-identified reference, not an independent specimen-based taxonomic determination. Source identification is retained. The rounded clasping leaf lobes and prickly leaf edges are shown for comparison with S. oleraceus; hybrids and other lookalikes require a full key.
Wikimedia server-resized derivative; no local crop, colour change or generative editing. Gallery display preserves the full image; catalog preview may use a CSS crop.

Identification

An annual with yellow flower heads and often glossy, prickly-edged leaves. Rounded basal leaf lobes clasp the stem, unlike the more pointed lobes of annual sowthistle. N-sonchus-asper U-sowthistle

People

Spiny leaf edges warrant care when handling. No ingestion safety has been established here. N-sonchus-asper

Evidence scope: Handling precaution inferred from leaf structure.

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.

Plants & habitat

It grows in gardens, roadsides and disturbed ground. Plants can bolt quickly, and seeds travel by wind and water. N-sonchus-asper

Management & timing

Inspect patches often and remove unwanted plants before fluffy seedheads form. N-sonchus-asper

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

References

C-floristic-2020 — Colorado Floristic Quality Assessment: 2020 Update, Colorado Natural Heritage Program, Colorado State University. Accessed 2026-09-07T02:27:33+00:00. Locator: Appendix B, Colorado species list: scientific name and native/non-native fields.
CO-rules-2025 — Colorado Noxious Weed Act rules, 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.
N-sonchus-asper — Sonchus asper, NC State Extension. Accessed 2026-09-07T02:23:12+00:00. Locator: Description, identification attributes and plant problems; toxicity section where present.
U-sowthistle — Annual sowthistle, University of California Statewide Integrated Pest Management. Accessed 2026-09-07T02:26:10+00:00. Locator: Named species or genus; identification, distribution and hazard sections where available.
S27 — 2103 – Colorado Noxious Weeds, PlantTalk Colorado · CSU Extension. Accessed 2026-09-07T00:23:57+00:00. Locator: List A, B and C management categories.

Content revised 2026-09-07 02:46:00Z · Source checks dated separately in the references.