Redroot or amaranthus retroflexus is a species of flowering plant in the family Amaranthaceae.

Redroot grows in soils that are low in Calcium and Phosphorus but high in Potassium and Magnesium. It likes well drained soils but it presences is likely to indicate lack of beneficial microbial activity and organic matter in the soil.

Like many other species of Amaranthus, this plant may be harmful and even deadly when fed to cattle and pigs in large amounts over several days. However, when supplied in moderation, it is regarded as an exceptionally nutritious fodder.

Red-root or pigweed amaranth, Amaranthus retroflexus, growing in Galicia, Spain