Amaranthus retroflexus

Scientific Name Amaranthus retroflexus L.
Common Names English: Redroot pigweed, common amaranth; German: Zurückgebogener Amarant, rauhaariger Fuchsschwanz; French: Amarante réfléchie; Spanish: Bledo
Description Annual, common seed weed, erect growth, 20-220 cm (7.87 - 86.6 inch) high depending on growing conditions.

Descriptions

Characteristic Features

Compact, caespitous inflorescence.

Cotyledons

Cotyledons longoval, 10-12 mm (0.39 - 0.47 inch), at the underside often redviolet.

Stems

Erect, single or branched, light green to reddish, more or less short and rough hairy.

Leaves

Long petiolate leaves, ovate, pointed, gray-green.

Propagatio Organs

Flowers

Borne in short, dense, sometimes branched spikes up to 20 cm (7.87 inch) long, green, each flower unisexual but with both the male and female flowers on the same plant.
Bracts about 6.5 cm (2.56 inch) long, longer than the sepals.

Flowering Period

May-September.

Fruit

Urticle, nearly globe-shaped, slightly rugose.

Seeds

Germination from late spring-summer. Seeds are lentiform, dark red-brown and shiny.

Viability Of Seeds

More than 40 years.

Propagation

By seed.
1,000-5,000 seeds/plant.

Occurrence

Habitat

A. retroflexus is found on dry, disturbed ground and especially cultivated or abandoned fields and burned areas, where it is a rapid colonist.

Soil

Redroot pigweed prefers warm and fertile soils.

Additional Crop Information

Crops with late canopy closure like row crops, vegetables, corn and vine yards, hybridizes with other pigweeds and amaranth crop.

Agricultural Importance

This aggressive weed is native to tropical America, but is found throughout the United States in disturbed areas. It greatly reduces yield and quality and interferes with combine harvesting. Because of its rapid growth and deep root system (more than 1 m; 39.37 inch) it competes for water and nutrition, therefore it is very resistant to drought. Redroot pigweed accumulates nitrate and may cause bloat in cattle.
It is partly resistant to Triazin herbicides and ALS inhibitors.

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