When saguaro cacti grow in their normal form, they rarely grow symmetrically. Saguaros sometimes grow in odd or misshapen forms. The growing tip occasionally produces a fan-like form which is referred to as crested or cristate. These crested saguaros are somewhat rare. Biologists disagree as to why some saguaros grow in this unusual form. Some speculate that it is a genetic mutation. Others say it is the result of a lightning strike or freeze damage.

Source
NPS