It pays to be prepared

Photo by Marty Horowitz 4/22/2015

Chainfruit (aka Jumping) Cholla (Cylindropuntia fulgida var. fulgida and var. mammillita) is prepared for change. Most of the time, this plant reproduces via cloning (i.e., a piece falls off - or attaches to you or another animal - takes root in the soil and grows a new plant).
As you can see from the gorgeous flower, it can also reproduce sexually (i.e., pollen fertilizes egg, egg develops into seed). The fruit persists on the plant (note the bumps in the upper right of the 2nd photo); the flowers actually bud from previous seasons' fruit. Sometimes the seeds within the fruit are not viable, it's true. But some are. And sexual reproduction means that the seed - and thus the plant - has different DNA from its parents.
If a virus, say, wiped out the clones, these plants could (conceivably) grow from seed. And vice versa.
It's a good thing the flower buds are edible, I say : -)