Astraeus hygrometricus, commonly known as the hygroscopic earthstar, the barometer earthstar, or the false earthstar, is a species of fungus in the Diplocystaceae family. Young specimens resemble a puffball when young and unopened. In maturity, the mushroom displays the characteristic earthstar shape that is a result of the outer layer of fruit body tissue splitting open in a star-like manner. The false earthstar is an ectomycorrhizal species that grows in association with various trees, especially in sandy soils. A. hygrometricus has a cosmopolitan distribution, and is common in temperate and tropical regions. Its common names refer to the fact that it is hygroscopic (water-absorbing), and can open up its rays to expose the spore sac in response to increased humidity, and close them up ag