Origin of umbonate
Examples from the Web for umbonate
When the center of the pileus is raised in the form of a boss or knob it is umbonate (Fig. 242).
The umbonate pileus and the nearly free, broad, gray gills will distinguish it.
This species differs from C. atrata in having an umbonate pileus.
It may be rounded and depressed (concave), elevated (convex), level (plane), or with a little mound in the centre (umbonate).Among the Mushrooms|Ellen M. Dallas and Caroline A. Burgin
The pileus is often umbonate or gibbous, and the center is often darker than the margin.