Ontario Weeds: Redroot pigweed
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Excerpt from Publication 505, Ontario Weeds,
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Table of Contents
- Name
- Other Names
- Family
- General Description
- Stems and Roots
- Flowers and Fruit
- Habitat
- Similar Species
- Related Links
Name: Redroot pigweed, Amaranthus
retroflexus L.,
Other Names: amarante à racine
rouge, Green amaranth, Pigweed, Redroot, Rough pigweed, Tall pigweed,
amarante réfléchie, armarante pied rouge
Family: Amaranth Family (Amaranthaceae)
General Description: Annual, reproducing
only by seed.
Redroot pigweed (A - young flowering plant with dull (non-shiny) leaves; B - thick inflorescence with short lateral branches).
Redroot pigweed. A. Base of plant. B. Top
of flowering plant.
Stems & Roots: Stems erect, 10cm-2m
(4in.-6½ft) high, but usually 50-90cm (20-36in.), simple or
branched, lower part thick and smooth, upper part usually rough with
dense short hair, greenish to slightly reddish but usually red near
the roots; leaves alternate (1 per node), long-stalked, ovate with
a shallow notch at the tip on young plants but on older plants somewhat
diamond-shaped, dull green above but lighter green and with prominent
whitish veins below, and somewhat hairy.
Flowers & Fruit: Inflorescence a
coarse, branching, bristly panicle made up of a short, thick terminal
spike and below it several to many short, lateral finger-like spikes,
these pointing upward if not crowded or outward if densely crowded,
and smaller spikes in some lower leaf axils, each spike made up of
many tiny flowers and spiny-tipped bracts up to 8mm (1/3in.) long;
each flower unisexual, having either 1 pistil or 5 stamens but never
both (similar to Prostrate
pigweed); seeds black, shiny, round, flattened with a narrow,
thin margin, and about 1mm (1/25in.) in diameter. Flowers from July
to August.
Habitat: Redroot pigweed is a common
weed in cultivated fields, gardens, pastures, waste places, roadsides
and other disturbed areas throughout Ontario.
Similar Species: It is distinguished
from Tumble pigweed and Prostrate pigweed by its tall, erect habit
of growth, its larger and broader leaves, and its flowers crowded
into a thick, terminal panicle as well as in some of the lower leaf
axils; from Smooth pigweed by its coarse, harsh inflorescence; and
from Green pigweed by the somewhat dull green colour of its leaves,
the dense covering of short hair on its upper stem, its thick, coarse,
bristly terminal panicle with the uppermost central spike extending
only a short distance above the rest of the panicle, and by two features
requiring magnification to see: the sepals of each flower are broader
above the middle and rounded or somewhat flattened at their tips,
and its male flowers usually have 5 stamens each.
Related Links
... on general Weed
topics
... on weed identification, order OMAFRA
Publication 505: Ontario Weeds
... on weed control, order OMAFRA
Publication 75: Guide To Weed Control
For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca