Cynanchum marnierianum is a drought resistant plant endemic to Madagascar. It has very tiny green flowers that form a whorl from an adapted sepal. It looks like dry dead sticks when not in bloom.
This is a Stapelia scitula! Stapelia/Huernia and related genera are known for their alien-like flowers that smell like rot and decay. They’re pollinated by flies who are attracted to the smell. This particular specimen has its own special corner of the greenhouse when it flowers.
Kihaku-Gato's Garden Blog (tumblr import) 