Amaranthus retroflexus is a species of flowering plant in the family Amaranthaceae with several common names, including red-root amaranth, redroot pigweed, red-rooted pigweed, common amaranth, pigweed amaranth, and common tumbleweed.

Outside of its native range, it is considered a weed. Leaves, stems and seeds may be eaten raw and cooked, the leaves have a high nutritional value.

When grown on nitrogen-rich soils they are known to concentrate nitrates in the leaves,

especially noticeable on land where nitrate fertilizer is used.