The cephalium is a specialized woolly or bristly area found on some cacti where flowering takes place. It is typically located on the top of the cactus.
The cephalium often appears like a cushion or pillow of hairs, spines, and trichomes from which flowers emerge. It may be a different color or texture than the rest of the cactus.
The cephalium is thought to provide protection, insulation, and aid in the development of flowers and seeds on these cacti. It represents a specialized growing point for reproductive structures.