Stapelia gigantea
Zulu Giant

This looks much like a miniature Cereus cactus, with a fat, upright, ribbed stem, but without spines, like all Old World cactus analogs. Though it grows to less than a foot tall, it produces a starfish-shaped flower that can be a foot across. Hardy outside only in the warmest climates, it grows easily in a sunny or partly-sunny window. It's really best to grow it in a greenhouse, though, if you can't grow it outside, or move it out when in bloom. That's because an alternative common name is 'Carrion Flower' and it is pollinated by flies. 'Nuff said, but I've noticed that this rather important fact is curiously omitted by other growers.
Native to South Africa.