Some weeds are pan-global. This means they grow pretty much everywhere except Antarctica and that botanists are hardly sure where they were originally native to. Dandelion, plantain and lamb's quarters, also known as pigweed, are in this group and are among the surest signs of human presence. Wherever we go, there they are.
Lamb's quarters have a particular affinity for places with rich soil, like vegetable beds. It's interesting because, while we consider it an annoying weed, in many parts of the world (Africa, India and Central America) it is cultivated as a valuable food crop. The leaves have a similar flavor and nutritional composition to spinach and the seeds are edible, too. As a grain, it resembles quinoa, a traditional staple in the Andes Mountains of South America— and popular here among health enthusiasts — that is closely related to lamb's quarters (both are in the Chenopodium genus). Why one sells for $8/pound on the shelves of health shops and the other we pay gardeners $8/hour to remove from our vegetable beds is a mystery.
Lamb's quarters were first domesticated in North America approximately 4000 years ago and are still farmed in Mexico, though they are slowly loosing favor. Perhaps, in another 4000 years the tides will turn again and we will be weeding out spinach from among our pigweed plants.