How is a old man cactus suited to it's habitat?

Senita or "senile" Old Man Cereus group cactus has hanging roots on the elbows of the upturned branches. When weight of the arm bends the roots take over, thus propagating and spreading forming bushclumps. The Cactus itself grows mainly in Mexico, with few in the American Southwest. The Old Man bears it's foul smelling pink blossoms at night on the six or seven ridge branch. Short spikes on the lower branches offer some protection from animals.