Amaranthus retroflexus aka Reflexed Amaranth

Amaranthus retroflexus is a fast-growing annual in the amaranth family. Its common names include pigweed and redroot amaranth. Kew lists Mexico as its native range. Other sources give broader ranges in North America or tropical America. People have introduced it across much of the world. It grows in fields, gardens, waste ground, and ditch banks. Disturbed soil helps it spread into new sites.

The plant stands upright, with few branches or branches near the top. One plant reference gives a height of 3 feet [0.9 metres]. Its wider reported range is 0.7–4.9 feet [0.2–1.5 metres]. Some plants reach 6.6 feet [2 metres]. The stout, round stem has white hairs and a reddish base. Green leaves grow in an alternate pattern along the stem. Their shapes range from oval to heart-shaped or diamond-shaped. The upper leaves are smaller than those near the base. Leaf tops are smooth, while hairs line the veins beneath. The undersides may show red or purple tones.

Small green flowers form dense spikes within branched panicles. Each plant bears both male and female flowers. Long bracts project beyond the flower parts. Flowers appear from July to September, and wind carries the pollen. The plant can also pollinate itself. Seeds ripen from August to October in small, pale capsules. Each capsule splits around its middle to release one seed. The glossy seed ranges from dark reddish brown to black. A single plant can produce as many as 117,000 seeds.

It needs full sun and fertile soil that drains well. It grows in sand, loam, or clay and prefers moist soil. It also tolerates drought. Warmth and shelter help it grow well. NC State lists it for USDA zones 3–11. Its spread can reduce yields in vegetable crops. That makes it a poor choice for most gardens. Birds, insects, and small mammals use it for food. Sources disagree about pests: one reports few damaging insects. Another warns that insects may chew its leaves.

People eat the young leaves raw or cooked. They also eat, toast, sprout, or grind the seeds. Indigenous North Americans once grew it as a food crop. The whole plant can yield yellow and green dyes. Records also describe leaf tea as a traditional astringent remedy. Food use does not mean the plant is always safe. Leaves can collect nitrates, especially in nitrogen-rich soil. Oxalates can also cause harm. Large amounts can poison livestock, including horses, cattle, and pigs.