Redroot Amaranth
Amaranthus retroflexus
Redroot Amaranth (Amaranthus retroflexus), also known as common amaranth, red-root pigweed, or wild beet, is a fast-growing annual flowering plant belonging to the Amaranthaceae family. It is one of of the most widespread and recognizable amaranth species across temperate and tropical regions worldwide.
Despite its reputation as a weed, redroot amaranth has been cultivated as a food crop for thousands of years by Indigenous peoples of the Americas. Its leaves, stems, and tiny seeds are all edible and highly nutritious. The name "retroflexus" refers to the plant's characteristic downward-curving (reflexed) flower bracts.
• Member of the Amaranthaceae family, which includes ~70 genera and over 900 species worldwide
• Considered one of the most aggressive agricultural weeds globally, yet also an ancient pseudocereal grain
• C4 photosynthetic pathway — highly efficient carbon fixation that allows rapid growth in hot, dry conditions
• Common names include red-root pigweed, common amaranth, rough pigweed, and wild beet
Taxonomie
It has since become one of the most cosmopolitan weed species on every continent except Antarctica:
• Naturalized across North America, Europe, Asia, Africa, and Australia
• Now considered one of the top 10 most economically damaging agricultural weeds worldwide
• Listed on invasive species databases in multiple countries due to its aggressive colonization of cultivated fields
Historical significance:
• Amaranth seeds were a staple grain of the Aztec civilization, called "huauhtli" in Nahuatl
• Aztecs used amaranth in ceremonial foods called "tzoalli" — molded dough figures mixed with honey and human blood offered to deities
• The Spanish conquest actively suppressed amaranth cultivation due to its association with indigenous religious practices
• Archaeological evidence of amaranth cultivation dates back at least 6,000–8,000 years in Mexico and the Andes
• In North America, Indigenous peoples including the Hopi, Navajo, and Zuni harvested wild A. retroflexus and related species for both food and dye
General Structure:
• Height: 30 cm to over 2 m (occasionally up to 3 m) depending on soil fertility and moisture
• Growth habit: Erect, branching from the base
• Stem: stout, angular, ridged, often reddish or reddish-green near the base (giving rise to the name "redroot")
• Root system: shallow but extensive taproot, characteristically reddish-pink in color
Leaves:
• Alternate arrangement; simple, ovate to rhombic-ovate shape
• Size: 2–15 cm long, 1–7 cm wide
• Margin: entire (smooth-edged), slightly wavy
• Texture: rough-surfaced (scabrous) with visible veins
• Petiole: long, often as long as or longer than the leaf blade
• Color: dull green to dark green above, paler beneath
Flowers:
• Small, greenish, inconspicuous, lacking petals
• Arranged in dense, terminal and axillary spike-like inflorescences (thyrses)
• Inflorescences can be 5–20 cm long, bristly and prickly to the touch
• Bracts are rigid, awl-shaped, and distinctly longer than the sepals (a key identification feature)
• Monoecious — individual plants bear both male and female flowers
Seeds:
• Tiny, lens-shaped (lenticular), ~1–1.5 mm in diameter
• Shiny, dark reddish-brown to black
• A single plant can produce 100,000 to over 500,000 seeds
• Seeds remain viable in soil seed banks for decades (up to 40+ years reported)
Habitat:
• Cultivated fields, gardens, roadsides, waste ground, riverbanks, and disturbed soils
• Prefers nitrogen-rich, fertile soils but tolerates a wide range of soil types
• Found from sea level to elevations of approximately 2,500 m
Climate & Growing Conditions:
• Warm-season annual; germinates when soil temperatures reach 15–20°C
• Peak germination in late spring to early summer
• C4 photosynthesis confers exceptional heat and drought tolerance
• Grows rapidly in full sun; intolerant of heavy shade
Reproduction & Dispersal:
• Exclusively seed-reproducing (annual life cycle)
• Seeds dispersed by water, wind, agricultural machinery, contaminated crop seed, and animal fur
• Seeds require light for germination and are most successful when buried less than 1–2 cm deep
• Can produce multiple flushes of seedlings throughout a single growing season
Ecological Interactions:
• Host plant for several insect species, including various beetles and moths
• Seeds are an important food source for granivorous birds such as sparrows, finches, and doves
• Can serve as an alternate host for certain crop pathogens and nematodes
• Known to develop herbicide resistance — populations resistant to glyphosate, ALS inhibitors, and triazines have been documented in multiple countries
Light:
• Full sun (minimum 6–8 hours of direct sunlight per day)
• Does not tolerate shade well
Soil:
• Adaptable to a wide range of soil types
• Prefers well-drained, fertile, nitrogen-rich soils
• Tolerates pH range of approximately 5.5–7.5
Watering:
• Moderate water needs; drought-tolerant once established due to C4 metabolism
• Consistent moisture promotes faster, more tender leaf growth
Temperature:
• Warm-season crop; optimal growth at 21–30°C
• Frost-sensitive; killed by the first hard frost
• Seeds germinate best at soil temperatures of 18–25°C
Propagation:
• Direct sow seeds on or very near the soil surface (seeds require light to germinate)
• Sow after last frost date when soil has warmed
• Seeds germinate in 4–10 days under optimal conditions
• Thin seedlings to 15–30 cm apart for leaf production; wider spacing for grain production
Common Problems:
• Aphids and leaf miners may attack young plants
• Can become invasive if allowed to set seed — remove flower heads before seed maturity
• Herbicide-resistant populations make chemical control increasingly difficult in agricultural settings
Wusstest du schon?
Redroot Amaranth is a botanical paradox — simultaneously one of the world's most despised agricultural weeds and one of humanity's oldest cultivated food plants. The "Living Seed Bank" Phenomenon: • A single redroot amaranth plant can produce over 500,000 seeds in one season • These seeds can remain dormant yet viable in the soil for 40 years or more • A single square meter of agricultural soil may contain tens of thousands of dormant amaranth seeds • This creates a "living seed bank" that can regenerate infestations decades after the last plant was seen Ancient Aztec Superfood: • Amaranth seeds were so central to Aztec culture that they were used as currency and in religious ceremonies • The Spanish conquistadors, recognizing its cultural importance, banned amaranth cultivation in the 16th century in an effort to suppress indigenous religious practices • This suppression was so effective that amaranth nearly vanished from cultivation for centuries Herbicide Resistance Champion: • Amaranthus retroflexus is one of the most herbicide-resistant weed species on Earth • It has independently evolved resistance to multiple herbicide classes, including glyphosate (Roundup), ALS inhibitors, and photosystem II inhibitors • In some regions, populations have stacked resistance to three or more herbicide modes of action simultaneously • This makes it a model species for studying the evolution of herbicide resistance C4 Photosynthesis Efficiency: • Redroot amaranth uses the C4 carbon fixation pathway, which is far more water-efficient than the C3 pathway used by most crops • C4 plants lose roughly half as much water per unit of carbon fixed compared to C3 plants • This is why amaranth can grow explosively fast in hot, dry conditions where other plants struggle • Scientists are actively studying C4 amaranth genes in hopes of engineering C4 photosynthesis into major C3 crops like rice and wheat
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