A pleated ink cap, my first toadstool of the year!

According to my good friend Prof. Google:
Commonly referred to as the Pleated Inkcap, and sometimes as the Little Japanese Umbrella, Parasola plicatilis is a very delicate member of the inkcap group of fungi. It occurs in short grass.
This is one of the many short-lived grassland fungi that appear overnight following rain; the fruitbodies develop, expand, shed their spores and decay within 24 hours and by the next morning there is usually no evidence of them ever having existed.