I admired a particular cactus last fall at the TNLA Expo, and stopped to talk with the vendor. Not only was this a (mostly) spineless cactus, it was also variegated emerald and lime green. Pretty sensational. This variegated type is the decorator version of the hardworking Opuntia ficus-indica, which I grow. No spikes means it is easier to tend, prepare, and eat. The vendor thought Opuntia ficus-indica has been selected for spinelessness since prehistory. That really intrigues me and I wanted to know more.
My cactus produced a spiny throw-back of a pad from the base the main trunk. I plucked it out. I’m curious what triggers going spineless to spiny. Luther Burbank developed cactus varieties for livestock feed, and wrote that many spiny cacti have spineless sports from time to time.