The Crested Saguaro

A rare example of a crested saguaro along the Sweetwater Trail in Saguaro National Park just west of Tucson, Arizona. Cresting occurs in approximately 1 in every 200,000 saguaros.

 From Wikipedia

Fasciation (or cresting) is a condition of plant growth in which the apical meristem, normally concentrated around a single point, producing approximately cylindrical tissue, becomes elongated perpendicularly to the direction of growth, producing flattened, ribbon-like, crested, or elaborately contorted tissue. The phenomenon may occur in the stem, root, fruit, or flower head.
Fasciation can be caused by a mutation in the meristematic cells, bacterial infection, mite or insect attack, or chemical or mechanical damage. Some plants may inherit the trait.
Fasciation is rare overall, but has been observed in at least a hundred different plant species, including members of Aloe, Celosia, Delphinium, Digitalis, Euphorbia, Forsythia, Primula, Acer, Prunus and many genera of Cactaceae (cactus) and Salix. Cresting results in undulating folds instead of the typical "arms" found on mature Saguaro cactus. Some varieties of Celosia are raised especially for their dependably fasciated flower heads, for which they are called "cockscomb".