Astraeus hygrometricus

Astraeus hygrometricus, often known as the 'hygroscopic earthstar, the barometer earthstar, or the false earthstar, is a Diplocystaceae fungus. When closed, young specimens resemble a puffball. When mature, the mushroom takes on the distinctive earthstar form, which is caused by the outer layer of fruit body tissue splitting apart in a star-like pattern.