Amaranth was a staple in the Mayan diet until the Catholic church banned it's use because they thought of it as 'pagan food'. In truth, amaranth was used ritualistically in addition to daily consumption. I have my own theories on that. The move to ban this plant may have been politically motivated with the intention of 'starving them out'. Well, it worked. To this day, Amaranth is a touchy subject so much so that it is banned in the US (since about 1976).
Regardless, amaranth is safe to eat. This nutritional powerhouse contains a plethora of vitamins and minerals as well as 2.5 to 3g of protein per 100g. If you consider "bread" a basic household good, then this is the plant to keep on your radar. The seeds, when cooked, baked and then crushed, make an excellent flour substitute.
Look for amaranth in between rows of corn. Be careful if you do harvest from a cornfield. The farmer may have used an herbicide to deal with the amaranth.
The leaves and seeds of amaranth are both edible. Be aware that amaranth does contain a scant amount of oxalic acid. In theory, cooking (blanch and shocking for example) does remove some of the oxalic acid content.
That reminds me. There are around 70 different classifications of 'amaranth'. When you search for amaranth, use the scientific name "amaranthus". Palmer amaranth, or pigweed, grows just about everywhere.
Now that you have Amaranth (Pigweed), what do you do with it?
Gather the seeds. Cook until soft. Spread on a cookie sheet and bake at 250 for 30 minutes or until dry. Grind to a powder. Store in an airtight container in a cool, dry place. Use it as a flour substitute.
Cook the seeds (1 cup seeds to 1 cup water) until soft. Add fruit, butter or syrup to make a warm cereal.
Eat the young leaves as a side dish. Blanch and shock before eating. The leaves can be bitter.