Rough Pigweed, or Amaranthus retroflexus, is also known as red-root amaranth, redroot pigweed, ped-rooted pigweed, common amaranth and common tumbleweed. It is native to the tropical Americas, but has spread to most of the continents.
Rough pigweed is an annual that grows to between one to three feet tall. It may either be void of branches or have very few. The stem is round, thick, light green and covered with white hairs. There are also small white veins which run in a longitudinal direction. The leaves grow in an alternate manner and can measure up to six inches in length and four inches across. These leaves are elliptical in shape and are smooth or have a slightly wavy edge. The base is can either be rounded or wedge-shaped. The tips are rounded with the tips being blunt. The central stem ends with as a stout stem with spikes of light green flowers. The flowers can grow up to six inches long. Some of these spikes of flowers can grow in the axillaries and are shorter than the terminal one. The spikes look bristly and have separate pistillate, or female, and staminate, or male, flowers. The pistillate have five white sepals, no petals and an ovary with three styles. The staminate has five white sepals, five stamens and no petals.
The sepals on the flowers are oblong with short, pointed or flattened tips. The base of the flower has one or more green bracts with long-pointed tips. Rough pigweed blooms from late summer to early fall. The blooming period is about one to two months. Pollination is accomplished through wind. The seeds are developed by the pistillate flower as a single seed encased in a membranous bladder or utricle
The utricle opens up and releases the seed. The seeds are either dark brown or black with a circular and flattened shape. The surface of the seeds is smooth and shiny.
The root is a short taproot that is usually red.
The rough pigweed grows best in a soil that has loam, clay-loam, or a gravelly texture. The size of the plant varies according to moisture it receives and richness of the soil. The seeds have a viability time of over 30 years.
Rough Pigweed can be found throughout most of Illinois. It is native to South America, but it enjoys any area that has disturbed prairies, hill prairies, cropland, fallow fields, farms, gardens, gravelly strips along railroads and roadways and waste areas.
Very few insects are associated with the flowers of the rough pigweed. The skipper, Pholisora Catullus or common sootywing, caterpillar feeds on the foliage as do other caterpillars. Pigs and cattle enjoy pigweed, although at times the leaves can cause bloating or symptoms of nitrate poisoning if it is eaten in large quantities. Deer and rabbits also eat it, but in a lesser quantity.
