Amaranthus retroflexus L.
Redroot pigweed is named for its red, thick taproot it develops. Often lower stems are also reddish in color. Redroot pigweed has a tall, usually erect habit, commonly found growing 2 to 4 feet tall. With little other vegetative competition, it can reach heights much greater. It develops lateral shoots that allow it to form tall clumps. If mowed repeatedly, this weed can grow and appear prostrate in habit. Mature plants have coarse hairy stems. Leaves vary in size up to about 7 inches and have noticeably long petioles. They are alternate along the stem having very prominent veins. Leaves lower on the plant are oval to diamond shaped, while upper leaves are lance shaped.
Inconspicuous green flowers cluster form dense terminal and auxiliary panicle like spikes. Flowering usually occurs in early summer through the first frost. This weed can flower when only several inches tall.
Favorable environment notes:
Redroot pigweed thrives in areas of disturbed soil common to agricultural crop lands such as field nurseries, orchards, row crops and vineyards. Sunny utility areas such as roadsides, pasture lands and landscaped areas are commonly inhabited by this weed as well. Redroot pigweed also can be a problem in outdoor container and gravel areas of nursery operations. It is often seen growing along the outside perimeter of greenhouses and occasionally inside the greenhouse near side vents.
Redroot pigweed reproduces only by seed. Seeds are very tiny (1/25th of an inch, 1 mm) shiny and dark colored.
This plant is nearly impossible to differentiate from related species Powell amaranth, A.powellii . It can be distinguished by close examination of the flower bracts. Powell amaranth has longer, narrower and more pointed bracts than redroot pigweed.