Redroot pigweed

Encyclopedia Article

Redroot pigweed                  Amaranthus retroflexus L.

Family: Amaranthaceae                             
Life cycle: Annual 
Native status: Native to North America
Habitat: Crop fields, waste areas               

General description: Erect, branched plant reaching heights of 6 ft.

Key ID traits: Stems hairy; leaves are egg-shaped and often reddish underneath and with wavy margins; first leaf usually has notch at tip. Linear cotyledons. Inflorescences has short (<6"), thick (1/4-1/2") branches with large bracts.

Similar species: Both smooth and redroot pigweed have hairy stems, whereas common waterhemp and Palnmer amaranth have smooth stems. The seedhead of redroot pigweed is more compact than those of smooth pigweed and common waterhemp.

Miscellaneous: Redroot pigweed was the dominant Amaranthus species in Iowa prior to the 1980’s, but was replaced by common waterhemp following the introduction of ALS inhibiting herbicides and the spread of herbicide resistance. Redroot pigweed and smooth pigweed are monoecious, whereas waterhemp and Palmer amaranth are dioecious.


Stems of redroot pigweed are pubescent. Hairs are most visible on new growth.

egg-shaped leaves
Egg-shaped leaves

Redroot pigweed (L) and waterhemp (R) seedlings.