Several years ago I was volunteering for the plant sale at the State Botanical Garden of Georgia in Athens and found a tiny, little piece of a plant that was being swept into the garbage. I figured rather than see it thrown away I'd take it home with me, stick it in a pot and see what happened.
What happened is what you see in the picture - my beautiful Prickly Pear Cactus, also known as Opuntia and it is at least 100 times the size of the original morsel I picked up off the floor.
This particular one is in bloom and is bearing red, edible fruit. It likes the hot, reflective environment of my deck and does not need much attention.