Gray Ghost Organ Pipe (Stenocereus pruinosus) (Buxbaum): Powdery blue-green columnar cactus from Mexico. In the wild, it can eventually grow to 20.0' with new branches sprouting from the base and trunk, but in cultivation it tends to stay under 6.0'. Young plants are deeply ribbed and have reddish brown spines, but with time the 5-8 ribs flatten and the spines turn white. When it blooms, it opens 2.0" to 3.5" white and magenta, funnel-shaped flowers in the nig