A small amount of canopy material is hand stitched around the bottom ring to form the inside rosette where the ribs meet the shaft.  

In addition, a small fold is made in the canopy where it fits over the shaft to form the outside rosette.

The stitching is a highly skilled task that takes years of practice to perfect.

These features are so expensive and time consuming that it has been discontinued on all but the highest quality umbrellas.