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Ohio State University Extension


Pigweed Identification Guide

Agriculture and Natural Resources
Bruce Ackley and Mark Loux, Horticulture and Crop Science

A number of pigweed species are found in Ohio. These species can become very problematic and reduce crop yields. Pigweed identification can be difficult, especially at the seedling stage of growth. This guide will help in making a correct identification based on typical pigweed characteristics.

Pigweed with hair on stems and leaves  

Pigweed with no hair on stems and leaves  

Smooth/redroot pigweed   Waterhemp Palmer amaranth   Spiny amaranth  
seedling image of smooth pigweed, with two sets of leaves seedling of waterhemp, with opposite leaves, five sets of green leaf pairs Seedling of palmer amaranth, five leaf sets, bright green close up of spikes close to leaf axil on spiny amaranth
Egg-shaped to round leaves   Long narrow leaves with short petioles   Petioles as long or longer than the leaf   Very long and sharp ¼–½ inch spines at leaf axils  

Palmer Amaranth (Amaranthus palmeri)

Closeup of a plant stem with green leaves and red stem, showing new leaf growth Underside of leaf with with petiole half as long a leaf Leaf with super long petiole on grey background
No or only sparse hair on leaves and stems Long petioles, as long or longer than the leaf
Weed in a green pot, with three sets of leaf rows Spike seedhead in the field on female plant, towering over rest of plant and crops
Ovate to diamond-shaped leaves (widest near the base)

Spike seedhead; rough to the touch on female plants

Waterhemp (Amaranthus rudis)

Closeup of waterhemp stem with blurry dark background Male waterhemp flower head on dark blue background Thin stalk of a female waterhemp plant on a black background.
No hair on leaves or stem Male waterhemp Female waterhemp
Long leaf with a short petiole on a black background Long leaf, front side, with a long petiole on dark background Waterhemp in a pot on a grated surface, with four leaf rows
Long lanceolate leaves Waxy leaf surface

Smooth/Redroot Pigweed (Amaranthus hybridus/retroflexus

closeup of a dusty green plant with a red stem, with tiny hairs on the stem Closeup of pigweed seedhead with fuzzy greenhouse in background slightly skinnier seedhead of the smooth pigweed, with fuzzy greenhouse in background
Fine hairs on stem especially near the newest growth Redroot pigweed Smooth pigweed
Front of a green leaf with a rough surface Pigweed plant with multiple green leaves with roundish oval leaves with fuzzy grey background
Rough leaf surface Round to oval leaves; widest near the middle

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Originally posted Aug 16, 2019.