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Ministry of Agriculture, Food and Rural Affairs

Pigweeds - REDROOT/GREEN

Redroot and green pigweed are common in southern Ontario, and are often both referred to as "redroot pigweed". They are similar in appearance and difficult to distinguish before the flowering stage. In areas where their distributions overlap, it is not uncommon to find both species growing together in the same field.

Scientific Names: Redroot pigweed, Amaranthus retroflexus L., Green pigweed, Amaranthus powelli S. Wats.,

Other Names: Redroot pigweed is also called amarante à racine rouge, Green amaranth, Pigweed, Redroot, Rough pigweed, Tall pigweed, amarante réfléchie, amarante pied rouge. Green pigweed is also called amarante de Powell, Green amaranth, Powell’s amaranth, Powell’s pigweed

Family: Amaranth Family (Amaranthaceae)

General Description: Annual, reproducing only by seed. Redroot and green pigweed are very similar in habit of growth, size and general appearance.

Habitat: Redroot pigweed is a common weed in cultivated fields, gardens, pastures, waste places, roadsides and other disturbed areas throughout Ontario. Green pigweed occurs throughout southern Ontario but is more abundant in the southwest; in some areas it is probably more important than Redroot pigweed

Seedlings

Redroot Pigweed Green Pigweed
  • Seedling with stem
  • Leaves alternate
  • Elongated cotyledons
  • Underside reddish-purple
  • Somewhat shiny green or slightly reddish-green colour
  • Less hairy stem and leaves

Stems

Redroot Pigweed Green Pigweed
  • Erect
  • 10 cm- 2 m (4 in. - 6 ½ ft) high, but usually 50- 90 cm (20- 36 in.)
  • 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
  • Erect
  • 10 cm- 2 m (4 in. - 6 ½ ft) high, but usually 50- 90 cm (20- 36 in.)
  • Simple or branched
  • Lower part thick and smooth
  • Less hairy stem

Leaves

Redroot Pigweed Green Pigweed
  • Alternate (1 per node)
  • Long-stalked
  • Ovate with a shallow notch at the tip on younger plants; on older plants somewhat diamond-shaped
  • Dull green above, lighter green and with prominent whitish veins below
  • Somewhat hairy
  • Alternate (1 per node)
  • Long-stalked
  • Ovate with a shallow notch at the tip on younger plants; on older plants somewhat diamond-shaped
  • Somewhat shiny green or slightly reddish-green
  • Less hairy

Flowers

Redroot Pigweed Green Pigweed
  • Inflorescence a coarse, branching, bristly panicle made up of a short, thick terminal spike 
  • Below, several to many short, lateral finger-like spikes, pointing upward if not crowded or outward if densely crowded
  • Smaller spikes in some lower leaf axils
  • Each spike made up of many tiny flowers and spiny-tipped bracts up to 8 mm (1/3 in.) long
  • Each flower unisexual, having either 1 pistil or 5 stamens but never both
  • Seeds black, shiny, round, flattened with a narrow, thin margin, and about 1 mm (1/25 in.) in diameter
  • Flowers from July to August
  • Inflorescence’s terminal spike is much longer (10- 25 cm, 4- 10 in.), narrower, about 1- 1.5 cm (2/5- 3/5 in.) thick, and either stands erect or hangs over a bit
  • Individual bristly finger-like spikes are usually longer (4- 12 cm, 2- 5 in.) and tend to point upwards
  • Flowers and bract about the same length
  • Male flowers usually have only 3 stamens
  • Flowers from July to September

Often Confused With
3- Seeded Mercury
Lamb’s-Quarters (Similar in habitat, often found growing together. At first leaf stage, lamb’s-quarters has opposite leaves, pigweed’s are alternate).

Redroot pigweed seedling  Redroot pigweed. A. Base of plant. B. Top of flowering plant Green pigweed seedling Green pigweed. A. Base of plant. B. Top of flowering plant Green pigweed seed head Redroot pigweed Underside of leaves of redroot pigweed
Click to enlarge.