Definitions

1. verb

to form or have a fringe or edge with hairs or other appendages that are stiff and often curved, especially in the manner of a thistle.

“The botanical illustrations showed plants that had leaves that ustulated with sharp, curved spines.”

2. verb

to have or develop a fringe or edge of stiff, often curved hairs, especially in the manner of a thistle.

“Some of the wildflowers in the meadow began to ustulate as they matured.”