On July 21, Roundup (Glyphosate)-resistant Palmer amaranth was reported to be “exploding” across central Kansas. This significantly affects the production of “Roundup Ready” crops of corn, soybeans and cotton and increases weed control costs. Palmer amaranth, a wild relative to the amaranth grains sold in health food stores, is usually known as Palmer pigweed and gained the “super weed” name from its resistance to Roundup. However, this label overshadows the brightness Palmer pigweed has to offer, which is especially valuable in the future of global warming.
Pigweed, the unappetizing name, may come from its use as fodder for pigs. There are nine pigweed species in the U.S. and Palmer pigweed causes farmers the most headaches. Native to eastern North America and thriving in disturbed soils, the expansion of agricultural lands has spread it to 30 states in southeastern U.S. (Roundup-resistant in about 20 states). It can grow one to two inches a day, reaching 12 to 18 inches in a few weeks, while cotton, for example, can stand no more than five to eight inches. Unlike other pigweeds, Palmer pigweed has separate female and male plants and female plants produce up to a hundred thousand seeds.
In a field where weeds outgrow crops, there is an uphill battle to control this “extremely aggressive” Palmer pigweed. Its impressive adaptation to the hot and dry condition represents a formula for success in a warming climate. Rather than fighting such a Nature-selected winner, finding the marketability of the weeds to turn them into crops is a lot easier.
And Palmer pigweed, or the more dignified name, Palmer amaranth, is edible and highly nutritious. The seeds have a high content of protein, fiber and Vitamins A and C. The greens are rich in iron, calcium, niacin, and Vitamins A and C. As a wild relative to the cultivated amaranth species, it produces seeds and leaves with equal nutrition. But it produces less seeds than the three grain amaranth species in cultivation, and its leaves only stay young and tender for a shorter time than the four vegetable amaranth species as crops.
Nevertheless, Southeastern American Indians once widely cultivated and relied on Palmer amaranth as one of the few summer vegetables in the deserts. They frequently consumed its leaves before the corn and beans could be harvested. A total of seven tribes ate Palmer amaranth and they prepared it in various ways, including fresh plants baked or boiled, leaves rolled into balls then baked for storage, and seeds grounded or dried.
Here are the mechanisms behind Palmer amaranth’s remarkable growth rate and drought-tolerance capacity. One of its tricks is diurnal leaf movements that keep leaf blades perpendicular to the sun to maximize carbon fixation. Its exceptionally high photosynthetic rate reaches optimum when leaf temperatures are between 95 and 115 °F, higher than that of most cultivated crops. And its photosynthesis process can continue except under the most extreme drought stress, thanks to an efficient water use. In the future of a warming climate, such a bright plant will either be super weed or super crop.
Additionally, its root system is special because it is larger than that of other pigweed and sturdier than that of most cultivated crops. Consequently, the roots can penetrate deeper for water and nutrients. Its fast seed germination and early seedling growth help Palmer amaranth to be a tough competitor as well.
Some foragers are concerned that the Roundup-resistant Palmer amaranth may be harmful to consume. But there is no scientific proof that the resistance impacts its taste, nutritional value or safety. How it gains herbicide resistance is not different from how some insects developed resistance to certain insecticides and some bacteria acquired resistance to certain antibiotics. The high reproduction rate hastens the happening of a random genetic mutation which can work around the killing chemical.
While the herbicide resistance of Palmer amaranth is not proven to cause any health issue, foragers seeking it need to be aware that this plant is a known nitrate accumulator and nitrates at excessive level can sicken people or animals. Therefore on agricultural lands, particularly non-organic farming lands, it may not be safe to eat due to applications of fertilizers. Leaves should be boiled for the nitrate to leach out before consumption (the water should be discarded). Like spinach and other leafy greens, it can also contain oxalic acid, which may be harmful to people with kidney problems.
In summary, Palmer amaranth is an extraordinarily efficient plant. The label of “super weed” disguises its edibility and valuable nutrition, and this plant has its own right to be considered as a crop just as the American Indians considered it in the past. Granted, there are drawbacks of Palmer amaranth as a food source, because its leaves will only be edible for a short period of time, its seed production is not as prolific as cultivated grain amaranth species, and it may contain excessive levels of nitrate.
Because of its heat loving and high drought stress tolerance, treating Palmer amaranth as a super weed would not only increase the control cost of farmers, but also waste the opportunity to utilize a crop thriving in the future of a warming climate. As a winner in nature and such a nutritious food resource, Palmer amaranth is so much more than a super weed and deserves to be researched for further improvement, just like many species of amaranths in other parts of the world which have been cultivated.
Opinion by Tina Zhang