Overview
Amaranthus retroflexus is a summer annual in the family Amaranthaceae reaching 12–72 inches (30–180 cm) tall. Stems are erect, stout, and rough-hairy, often branching from the base, with a reddish to pinkish taproot that gives the plant its common name. Leaves are alternate, ovate to rhombic, 1.5–6 inches (4–15 cm) long, dull green with prominent veins on the underside, borne on long petioles. Flowers are small, greenish, and densely packed into stiff, bristly terminal and axillary panicles 2–8 inches (5–20 cm) long. A single plant produces 100,000 to over 200,000 seeds. Seeds are small, round, glossy black, approximately 0.04 inch (1 mm) in diameter, and remain viable in soil for 10–40 years. Foliage accumulates nitrates and oxalates, particularly when growing in nitrogen-rich soils, making it toxic to livestock when consumed in quantity. Classified as a major agricultural weed worldwide, competing with row crops for water, nutrients, and light. Some populations have developed resistance to ALS-inhibiting and triazine herbicides.
Native Range
Native to tropical and subtropical regions of the Americas, with the precise center of origin uncertain. Naturalized on every continent except Antarctica, occurring from sea level to approximately 7,500 feet (2,300 m) elevation in disturbed agricultural land, roadsides, gardens, and waste areas.Suggested Uses
Used in weed science research, particularly in studies of herbicide resistance evolution. Young leaves are edible when cooked and have been consumed historically as potherbs. Seeds are consumed by ground-feeding birds including sparrows and finches. Included in agricultural weed identification curricula.How to Identify
Appearance
Size & Dimensions
Height1' - 6'
Width/Spread1' - 2'
Bloom Information
Flowers from June through October, triggered by day length shortening below approximately 14 hours. Individual plants bloom over 4–6 weeks. In the Pacific Northwest, peak flowering occurs in August through September. Seeds begin maturing 3 weeks after pollination; wind-pollinated.Detailed Descriptions
Foliage Description
Dull green, ovate to rhombic with prominent veins on the undersideGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight