Redroot Pigweed

Amaranthus retroflexus

Leaves: Oval- to diamond- to egg-shaped with prominent veins and wavy leaf margins. A V-shaped watermark can sometimes be seen on the blade surface. The undersides of leaves (especially the main vein) may be hairy. Leaf petioles are shorter or no longer than the leaf.

Stems: Covered in many fine hairs.

Height: 3-6 feet tall.

Flowers: Male and female flowers are produced on the same plant (monoecious) in terminal flower spikes that are comprised of short, thick, and compact branches. Easily confused with smooth pigweed; look to the presence of hairs and the flowerhead for confirmation.

Herbicide resistances in US: WSSA 2, 5, 14.

Redroot pigweed leaves with wavy leaf margins

Images above: Redroot pigweed leaves have wavy leaf margins, similar to the leaves of smooth pigweed.

hairy redroot pigweed parts — Stems, petioles, underside of leaves/veins can be very hairy.

Images above: Stems, petioles, underside of leaves/veins can be very hairy

hairy redroot stem — Redroot pigweed stems are exceptionally hairy

Redroot has the hairier stems than smooth pigweed

Images above: Redroot pigweed stems are exceptionally hairy.

Images above: Redroot pigweed flower heads can have many short and stubby branches

redroot pigweed seedling — Redroot pigweed seedling.

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

Redroot pigweed vs. smooth pigweed (stems)

Stems of smooth pigweed are hairiest on the upper stems

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

Redroot pigweed vs. smooth pigweed (flowers)

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

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).