Here is what blooms every year without care, totally forgotten, rarely watered and not re-potted for many years.
I grew this adenium from a seed, it is about 6 years old. It spends summers outside in full sun, grows leaves and branches, gets water from the rains and blooms. When cold days come - I take it inside, where it usually looses most of the leaves and does nothing until spring.
I think it is the easiest houseplant to grow.