Native to most of the American Southwest and Mexico, Opuntia engelmannii var. subarmata is a common "Prickly Pear" cactus with interesting pads with scalloped edges. It forms 4 to 6 foot high clumps 10 to 15 feet across. It's flowers are yellow with a green center and the plant blooms from April to May.
     Found some of this growing in an alley in Tucson and took a few cuttings. Hopefully it will grow well for me. I like the shape of the pads. Below is a small patch of it at Tucson Botanical Gardens.