Calvatia bovista

Calvatia bovista is a species of Calvatia mushroom, the second largest Calvatia in North America. As with other Calvatia mushrooms, it is edible when young, and it is used in medicine.

Description
The fruiting body is 10 to 25 cm high and 5 to 25 cm wide, round on top with a wide stemlike sterile base, often half the height of the fruiting body. Spores are 4-6μm, round, minutely warted or spiny. It is seen in pastures, open woods, etc., fairly common.