Figure 1. Mature Amaranthus retroflexus plant (4)
Figure 2. Image of leaf of Amaranthus retroflexus (3)
Figure 3. Example of taproot system found in Amaranthus retroflexus (1)
Figure 4. Distribution of Amaranthus retroflexus in Utah (2)
Description:
Amaranthus retroflexus, more commonly known as redroot pigweed, is a dicotyledonous annual and a member of the pigweed family Amaranthaceae. It is classified as a therophyte life-form in the Raunkiaer classification system. A therophyte is characterized as being able to survive in unfavorable seasons in the form of seeds and competing when the environment becomes more favorable for growth. Redroot pigweeds are sensitive to cold temperatures. Though both sexes may be found on the same plant, Amaranthus retroflexus is considered to be monoecious as each individual flower has a determined sex, being either male or female. It depends on wind pollination in order to facilitate fertilization.Amaranthus retroflexus stems are relatively tall, ranging between 0.3 and 2.0 meters (1.0 – 6.6 feet) in height. Its leaves are also relatively large with leaves ranging between 2.0 and 10.0 centimeters (2.0 – 10.0 cm) in length. Redroot pigweeds rely on a taproot system for nutrient absorption from the soil. The taproots range between 9.9 and 241.3 centimeters (3.9 – 95 in) in depth.
Geographic and Elevation Distribution:
Redroot pigweeds are native to tropical regions of the American continents, but have now become widespread throughout the whole world. They can be located throughout the entire North American continent, from Canada to Mexico and from the west coast to the east coast. They are also common throughout Europe, South America, and Africa. Once established, redroot pigweeds are hard to eradicate but can be controlled with the use of herbicides. These herbs are able to grow in a wide variety of environments and appear in cultivated fields, gardens, orchards, stream valleys, shores, prairie ravines, roadsides, and fence rows. In Utah, it has been noted that redroot pigweeds do not grow well on gravel, dense clay, or saline soils.As a result of inhabiting a wide variety of environments, redroot pigweeds can be found in a variety of elevation ranges. In Montana, pigweeds have been found in elevations as low as 2300 feet above sea level (700 meters). In Wyoming, pigweeds have been identified in elevations as high as 7800 feet above sea level (2377 meters). In Utah, redroot pigweeds are common in elevation ranges between 4400 and 4700 feet above sea level (1341 – 1433 meters).
Ecological Significance:
Amaranthus retroflexus is a very fire-resistant plant. Although the plants may physically die within the fire, they are able to re-germinate from their seeds if the environmental conditions are favorable. If a fire kills the plants late in the growing season, the plants typically will re-germinate the following spring. Fires also make it easier for Amaranthus retroflexus to establish. Redroot pigweeds will typically not establish in high-density vegetation areas. By clearing the land and eliminating competitor species, redroot pigweeds are able to easily establish after fires.A. retroflexus have importance to the diets of many animals. Cattle, pigs, sheep, and goats commonly eat redroot pigweeds as a source of protein. However, A. retroflexus has harmful effects on the kidneys of these animals and can cause bloating due to the large amounts of nitrates these plants are able to accumulate. As the plants become more mature, they become more unpalatable due to the rough, thorn-like structures in the flowers.
A. retroflexus conduct photosynthetic activity via the more efficient C4 pathway of photosynthesis. This pathway makes the plant more tolerant of hotter and drier environmental conditions and maybe responsible for success of this plant.
Medical Uses:
This plant can be used as an astringent in order to treat multiple medical conditions such as copious menstrual and intestinal bleeding. An astringent is a substance used to constrict the tissues or vessels of the body in order to reduce the amount of discharge of bodily fluids such as mucus or blood. The leaves are usually made into a tea and are drunk orally.References: 1. Altland, James Pigweed Roots. Retrieved November 10, 2007, Web site: http://oregonstate.edu/dept/nursery-weeds/weedspeciespage/REDROOT/pigweed_roots.html
2. Ramsey, R. D. Digital Atlas of the Vascular Plants of Utah. Retrieved November 10, 2007, from Amaranthus retroflexus Web site: http://www.nr.usu.edu/Geography-Department/utgeog/utvatlas/family/amar/amrez.html
3. Redroot Pigweed. Retrieved November 10, 2007, from Virginia Tech Weed Identification Guide Web site: http://www.ppws.vt.edu/scott/weed_id/amare.htm 4. Saint Mary's College of California, (1995). CalPhotos. Retrieved November 28, 2007, from CalPhotos Photo Database Web site: http://calphotos.berkeley.edu/cgi/img_query?query_src=photos_index&where-taxon=Amaranthus+retroflexus 5. Walsh, R. A. (1993). Amaranthus retroflexus. Retrieved November 11, 2007, from Index of Species Information Web site: http://www.fs.fed.us/database/feis/plants/forb/amaret/all.html#FIRE%20ECOLOGY