spiny composite

Spiny Amaranth

1- to 4-foot-tall plants, populations resistant to two herbicide groups have been found in the U.S. outside of the Northeast and Mid-Atlantic...

Spiny Amaranth

Amaranthus spinosus

Leaves: Oval- to diamond- to ovate shaped with smooth leaf margins. Hairless with v- shaped variegation present. Leaf petioles are shorter or no longer than the leaf blade. 

Stems: Hairless with pairs of spines emerging from leaf axils. 

Height: 1-4 feet tall. 

Flowers: Male and female flowers are produced on the same plant (monoecious). Inflorescences consist of long loose clusters with spiny bracts and some branching. 

Herbicide resistances in US: WSSA Groups 2, 9. 

Herbicide resistances in Mid Atlantic and New England: None Reported.

Resistance information updated April 2025.

spiny amaranth plant
spiny amaranth stem

Images above: Spiny amaranth plant (left). Stems (right) are hairless with pairs of spines emerging from leaf axils. 

spiny amaranth spines in leaf axil

Image above: Spiny amaranth stems are hairless with pairs of spines emerging from leaf axils. Flower stem (left) and upper stem (right). 

spiny amaranth plant
spiny amaranth leaves

Image above: Spiny amaranth plant (left). Leaves (right) are oval- to diamond- to ovate shaped with smooth leaf margins, and hairless with v- shaped variegation present. Leaf petioles are shorter or no longer than the leaf blade.

seedling
spiny amaranth seedling

Images above: Spiny amaranth seedlings.

spiny flower
spiny flower

Images above: Spiny amaranth inflorescences bear both male and female flowers, and the female flowers have sharp spines.  These greenhouse-grown plants don't show the typical loose clusters typical of plants in the field.

spiny amaranth flower

Image above: Spiny amaranth flower