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Thorny Pigweed Amaranthus spinosus


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Thorny Pigweed
credit: Dinesh Valke/CCSA

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Alternate name: Spiny Amaranth

Family: Amaranthaceae, Amaranth view all from this family

Description Annual herb with clusters of very small greenish-yellow flowers on a strong, bushy, upward-reaching, multi-branched occasionally reddish-tinged stem; each node with paired, divergent spines.
Flowers: Usually five sepals and no petals with female flowers occurring in dense, round clusters; male flowers in thin, terminal spikes up to 6" (15 cm) long; interspersed with spiny bracts as long as sepals.
Leaves: 1-3" (2.5-7.5 cm) long, ovate to elliptic to lanceolate; each leaf-axil bearing a pair of fine and slender to stout, compressed spines up to 1" (2.5 cm) long.
Height: Up to 4' (120 cm).

Flower July through October.

Habitat Cultivated soil, disturbed ground, and waste places.

Range Native to the tropical Americas but introduced on most continents. In Canadian provinces of Manitoba and Ontario. United States from Maine south to Florida, west to Texas, and north to Minnesota; also California, Hawai'i, Puerto Rico, Virgin Islands.

Discussion Commonly known as the spiny amaranth, prickly amaranth or thorny amaranth. Amaranthus species, despite being known as a common weed, produce large amounts of seed-like fruit; an important food for many songbirds.

In Asia it can be a serious weed of rice cultivation. In Cambodia in addition to being eaten, one of Spiny Amaranth's many other uses was that its ash was used as a grey dye for cloth. It is both eaten and used to treat various ailments in traditional African medicine.