Redroot pigweed  (Amaranthus retroflexus)

Redroot pigweed, a summer annual broadleaf plant, is found up to 7900 feet (2400 m) in the Central Valley, northwestern region, central-western region, southwestern region, Modoc Plateau, and most likely in other California areas. It thrives in open, sunny places inhabiting agricultural land other disturbed places. Because redroot pigweed can hybridize with other amaranth species, identification to species can be difficult. The plant is named for its pinkish to red taproot. Under certain conditions, free nitrates in redroot pigweed leaves are high enough to be toxic to livestock when consumed. Immediately before flowering, plant levels of nitrate are the highest and oxalate levels can also increase. However, in California there have been no reports of redroot pigweed poisonings in livestock. Actually, because they are rich in nutrients, redroot pigweed has been suggested as forage by some scientists.

Habitat

Crop fields, vineyards, orchards, pastures, gardens, landscaped areas, roadsides, ditch banks, and other disturbed places.

Seedling

Cotyledons (seed leaves) are long, narrow, lance shaped, and often have reddish undersides. Often the cotyledon stalk is reddish, too. The first leaf is egg shaped and has a notched tip. True leaves are much broader than the cotyledons, have notched tips, and their lower surface and main veins are often reddish. Leaves are alternate to one another along the stem. Leaf stalks are generally hairy along the edges.

Mature plant

Mature plants may grow up to almost 10 feet (3 m) tall but in general are found growing to about 3 ft (1 m).  The mature plants have coarse stems, and upper stems that range from hairy to densely hairy. Leaves generally range from 3/5 to 7 inches (1.5–17 cm) long and leaf stalks are 2/5 to 3 inches (1–8 cm) long. Lower leaves are egg to diamond shaped and upper leaves are usually lance shaped. Leaves have prominent veins, are stalked, and are alternate to one another along the stem.

Flowers

Flowering occurs from June through November. Flowering branches are densely packed with flowers. Inconspicuous flowers cluster to form dense, usually stiff, spikelike terminal clusters with smaller clusters between the main stem and leaf stalks.

Fruits

The fruits are tiny capsules, less than about 1/17 of an inch (1.5 mm) long. Fruit open around the middle by a caplike lid to release one seed each.

Seeds

Seeds are round, roughly 1/25 to 1/17 of an inch (1–1.5 mm) in diameter, glossy, and dark reddish brown to black.

Reproduction

Reproduces by seed.

Related or similar plants

• Palmer amaranth, Amaranthus palmeri
• Smooth pigweed, Amaranthus hybridus

More information

• Broadleaf ID illustration
• Calflora's distribution map
• For agriculture: UC IPM Pest Management Guidelines