smooth pigweed key characteristics

Smooth Pigweed

Grows 3 to 6 feet tall and populations resistant to two herbicide groups have been found in three states in the Northeast and Mid-Atlantic...

Smooth Pigweed

Amaranthus hybridus

Leaves: Oval- to diamond- to egg- shaped with wavy leaf margins. The undersides of leaves are not hairy*. Leaf petioles are shorter or no longer than the leaf blade. V-shaped variegation present.

Stems: Light green with red at the base and sparsely hairy- to hairy- especially upper stems (but less hairy than redroot pigweed). 

Height: 3-6 feet tall. 

Flowers: Male and female flowers are produced on the same plant (monoecious). Inflorescences consist of terminal flower spikes with branches that are thinner and less compact than redroot pigweed. 

Herbicide resistances in US: WSSA Groups 2, 4, 5, 9, 14. 

Herbicide resistances in Mid Atlantic and New England: WSSA Groups 2, 5 (DE, MD, NJ, NY, PA, VA)

Resistance information updated April 2025.

smooth pigweed wavy-margined leaves and hairy stem
Smooth pigweed plants have egg-shaped leaves with wavy margins (left) and hairy stems (right).
smooth pigweed flowerhead
Smooth pigweed has many pencil-thin floral branches.

Images above (left to right): Smooth pigweed plants have egg-shaped leaves with wavy margins, hairy stems and many pencil-thin floral branches.

Smooth pigweed vs. redroot pigweed (leaves)

leaves of smooth pigweed
Leaves of smooth pigweed have wavy leaf margins and look similar to Redroot pigweed.
Underside of redroot pigweed leaf with prominent hairs
Underside of redroot pigweed leaf with prominent hairs

Images above: Leaves of smooth pigweed (left) have wavy leaf margins and look similar to redroot pigweed. The underside of redroot pigweed leaves (right) have prominent hairs.

Smooth pigweed vs. redroot pigweed (stems)

Stems of smooth pigweed are hairiest on the upper stems
Stems of smooth pigweed are hairiest on the upper stems
Redroot has the hairier stems than smooth pigweed
Redroot has the hairier stems than smooth pigweed

Images above: Redroot pigweed stems (right) are hairier than smooth pigweed stems (left), which are hairier on the upper stems.

Smooth pigweed vs. redroot pigweed (flowers)

Smooth pigweed flower heads
Smooth pigweed flower heads have many, slender branches
Redroot pigweed flower heads
Redroot pigweed flower heads have short, stubby branches

Images above:  Smooth pigweed flower heads (left) have many, slender branches. Redroot pigweed flower heads have short, stubby branches (right).

Smooth pigweed and redroot pigweed are difficult to differentiate from each other, especially when plants are young and actively growing. Before flowering, look for the presence of hairs on stems and petioles and leaf midribs (redroot pigweed).

At flowering, look for thin, pencil-sized branches (smooth pigweed) or thick, short branches (redroot pigweed).

Smooth pigweed cotyledons
Smooth pigweed cotyledons
Smooth pigweed seedling
Smooth amaranth seedling

Image above: Smooth pigweed cotyledons (left) and seedling (right).