The steep, blackish cones comprising old Protea glabra flowerhead receptacles contribute to the species identification: Other South African proteas generally have flat receptacles hidden on the plant under old dry flowerheads retained for long periods. P. glabra has cones that are exposed soon on the plant and retained there for long without covering detritus.

The cone surfaces are dotted with little cavities where the perianths and later seeds had grown, long ago before dispersal. The dots are arranged in neat geometric curves, approximating Fibonacci spirals and "golden spirals", mathematically defined functions and number series.

Similar spirals are found in many natural plant and animal shapes and repeated in human art and culture (Rourke, 1980; Manning, 2007; Coates Palgrave, 2002; iNaturalist; Wikipedia).