Redroot pigweed
Discuss this plant with the guide — choose this profile as a possible match and prepare your observations for Colorado Plants & Practical Care.
Amaranthus retroflexus
Common weed; not an A/B/C listing in the reviewed state rule. CO-rules-2025
Crop competition; nitrate and oxalate livestock risk. Exposure help.
Identification caveat: Pigweed is used for several unrelated or similar-looking plants. Routt County’s prostrate pigweed entry concerns A. blitoides and is not used as exact A. retroflexus evidence.
Still researching this plant
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.
Lynk media · 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. Several pigweed species are similar. These are source-identified A. retroflexus; an unknown specimen may require close floral and pubescence characters to separate related Amaranthus.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
AnRo0002 · 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. Several pigweed species are similar. These are source-identified A. retroflexus; an unknown specimen may require close floral and pubescence characters to separate related Amaranthus.
Wikimedia server-resized derivative; no crop, color change, or generative editing. Gallery display preserves the full image; the catalog preview uses a CSS crop.
Javier martin · Public domain
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. Several pigweed species are similar. These are source-identified A. retroflexus; an unknown specimen may require close floral and pubescence characters to separate related Amaranthus.
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
An upright annual with hairy stems and dense green flower clusters; the lower stem or root may be reddish. N-amaranthus-retroflexus
Plants & habitat
A Colorado garden and field weed that competes strongly with crops and replenishes a seedbank. C-descriptions N-amaranthus-retroflexus
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
Nitrate and oxalate accumulation can poison livestock. Conditions affect risk, so a plant’s appearance does not establish forage safety. N-amaranthus-retroflexus
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
- 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-amaranthus-retroflexus — amaranthus retroflexus — Plant Toolbox, NC State Extension. Accessed 2026-09-07T01:04:56+00:00. Locator: Description; Attributes; Problems; Poisonous to Humans.
- C-descriptions — Weed descriptions, Colorado State University Extension. Accessed 2026-09-07T00:24:02+00:00. Locator: Species entries.
- 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.