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Astraeus hygrometricus, commonly known as the hygroscopic earthstar, the barometer earthstar, or the false earthstar, is a species of fungus in the family Astraeaceae. In maturity, it displays the characteristic earthstar shape that is a result of the outer layer of fruiting body tissue splitting open in a star-like manner. Despite its outward appearance, A. hygrometricus is not related to the genus of true earthstars, Geastrum, although historically, it has been taxonomically confused with them. First described in 1801 as Geastrum hygrometricus by Christiaan Hendrik Persoon, in 1885 Andrew P. Morgan showed that microscopic differences from other Geastrum species were enough to warrant it being moved to the new genus Astraeus. Several Asian species formerly thought to be A. hygrometricus were renamed in the 2000s once phylogenetic analyses revealed they were unique Astraeus species.

It 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 again in drier conditions.