In the dry areas of the Prairie in Alberta encountered this low growing cactus. It’s beautiful wide flower above the prickly stems. I think this would make a good green roof plant in central North America.
The Prickly Pear Cactus was used by the First Nation people as a food. Apparently they roasted the plant stems, having removed the thorns. Full of minerals and vitamins, the water in the stems was also an emergency water supply.