How to identify pigweeds

Pigweed species (Amaranthus spp.) can be difficult to distnguish from each other. But identification is crucial for developing a successful weed management program, particularly in an agricultural landscape that is heavily reliant on herbicides and where herbicide resistance is common. Pigweed species can also differ in their growth rates, which can impact the success of physical management, like cultivation.

When thinking about pigweed identification, focus on a few key characteristics:

The shape of the leaf blade and the length of the petiole, as well as the hairiness of the stem.
The presence of male and female flowers on the same (monoecious) plants or separate (dioecious) plants, and the structure of the flower heads (inflorescence).
The size of the plant.

composite image comparing pigweed leaves

composite image comparing pigweed flowerheads

In the above two pictures, the top row shows the leaves and flower heads of smooth pigweed, redroot pigweed, and Powell amaranth (left to right). The bottom row shows the leaves and male and female flowers of waterhemp (left) and Palmer amaranth (right). Despite similarities across species, there are traits/combinations of traits that can be used to distinguish among the pigweeds to successfully identify them.

Identifying traits of nine pigweed species

Species	Leaves and petioles	Stems and plant height	Male and female flowers	Flower heads	Herbicide resistance (MOA group, Northeast and Mid-Atlantic states where detected)*
Palmer amaranth Amaranthus palmeri	Diamond /ovate/linear Smooth/wavy margins May have V-shaped variegation Hairless Petiole LONGER than leaf blade	Green, red, or striped Hairless /sparse hair Erect, up to 10 feet	SEPARATE plants (dioecious)	Spiny bracts Tight clusters Thicker than a pencil 1- to 2-foot terminal spikes, sparse branches	2, 5, 9, 14 CT, DE, MD, NJ, NY, PA, VA
Waterhemp Amaranthus tuberculatus	Long, linear/oval Smooth margins No variegation Hairless Petiole shorter than leaf blade	Green, red, or striped Hairless Erect, up to 10 feet	SEPARATE plants (dioecious)	No spines Loose clusters Thinner than a pencil 1- to 2-foot terminal spikes, sparse branches	2, 5, 9 CT, DE, PA, NY
Powell amaranth Amaranthus powellii	Diamond Smooth margins May have V-shaped variegation Hairless / sparse hair Petiole shorter than leaf blade	Green, red, or striped Hairless /sparse hair Erect, 2 to 6 feet	Same plant (monoecious)	Spiny bracts Loose clusters Thicker than a pencil Sparse branches, 4 to 8 inches	5 NY (suspected)
Redroot pigweed Amaranthus retroflexus	Oval/diamond/ovate Wavy margins May have V-shaped variegation Hairy underside & midvein Petiole shorter than leaf blade	Light green w/ red base Very hairy especially upper stems Erect 0.5 to 7 feet	Same plant (monoecious)	Spiny bracts Tight clusters Thicker than a pencil Many branches, < 2 inches	2, 5, 9 CT, DE, MD, ME, NH, PA, VA, VT, WV
Smooth pigweed Amaranthus hybridus	Oval/diamond/ovate Wavy margins May have V-shaped variegation Hairless Petiole shorter than leaf blade	Light green w/ red base Sparse to very hairy (< redroot) Erect 2 to 7 feet	Same plant (monoecious)	No spines Tight clusters Thinner than a pencil Many branches, 1.5 to 3 inches	2, 5 DE, MD, NJ, NY, PA, VA
Purple (livid) pigweed Amaranthus blitum	Wedge-shaped, deeply notched tip Smooth margins No variegation Hairless Petiole shorter than leaf blade	Green to red/brown Hairless Prostrate to busy, 3 to 4 feet	Same plant (monoecious)	No spines Loose clusters Thinner than a pencil Unbranched, flowers at leaf axils	2 NJ
Spiny amaranth Amaranthus spinosus	Oval/diamond/ovate Smooth margins May have V-shaped variegation Hairless Petiole shorter than leaf blade	Pairs of spines at leaf base Hairless Erect, 1 to 4 feet	Same plant (monoecious)	Spiny bracts Loose clusters Thinner than a pencil Long spikes, some branching	None detected in Northeast or Mid-Atlantic
Tumble pigweed Amaranthus albus	Ovate/obovate/spatulate Wavy margins No variegation Hairless/sparse hair Petiole shorter than leaf blade	Pale green- to white Hairless 0.5-3 feet in diameter with low/bushy appearance	Same plant (monoecious)	Spiny bracts emerging from leaf axils Tight clusters	None detected in Northeast or Mid-Atlantic
Prostrate pigweed Amaranthus blitoides	Obovate/spatulate Wavy margins May have V-shaped variegation Hairless Petiole shorter than leaf blade	Green to red/purple, flexible Hairless 0.5-2 feet in diameter with low sprawling appearance	Same plant (monoecious)	Spiny bracts emerging from leaf axils Tight clusters	None detected in Northeast or Mid-Atlantic

*Herbicide resistance information updated April 2025. Find more information about herbicide resistance on this site.