That’s a bloom sticking straight out from the side of the plant into the black backdrop.
Why? What did you think it was?
Let’s talk Family Resemblance. These look like they should be related to the Stapeliads. Are they? Let’s check.
Well, they’re in Apocynaceae which is, as we all know, is known as the…. Dogbane Family!
And what’s the Sub-Family? Asclepiadoideae! Hmmm. Didn’t that used to be it’s own family? Asclepiadaceae? The Asclepiads? Yes! Yes, it did. And what about the Stapeliads? Have we forgot the Stapeliads? Well now they’ve decided to give the Stapeliads their own Tribe in the Asclepiads Subfamily of the Dogbane Family. And that Tribe is called… Stapeliae. Huh. So they are related, but not quite the same tribe. Good to know.
(also, they’re related to the Hoyas, too.)