This UFO-shaped plant is dioecious (unisexual). I think the plant pictured is male, but I'm not completely sure. On my to-learn list is better positive identification of the sex of euphorbia blooms (called cyathia).
With any luck, I'll have a breeding pair of these choice succulents from southern Africa. Here's my second plant. Look at the cute second body! This kind of branching is quite unusual in this species:
Euphorbia obesa grows wild in the Graaff-Reinet district in the Eastern Cape. The form pictured here (subspecies symmetrica) is found in the Willowmore district, where it's protected voluntarily by some farmers, partly with the effort of enthusiasts from the Euphorbia Study Group of Warrington, England.
The subspecies symmetrica is distinguished from the base type by a rather technical distinction: it produces multiple peduncles from single flowering eyes. Amateur growers and fans of this plant also know that Euphorbia symmetrica stays compact, rather than elongating and growing tall like the species type, Euphorbia obesa.
Euphorbia obesa ssp symmetrica at Cactus-Art.Biz