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.

[2] 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, then close them up again in drier conditions.

Despite a similar overall appearance, A. hygrometricus is not related to the true earthstars of genus Geastrum, although historically, they have been taxonomically confused.

In 1885, Andrew P. Morgan proposed that differences in microscopic characteristics warranted the creation of a new genus Astraeus distinct from Geastrum; this opinion was not universally accepted by later authorities.

Several Asian populations formerly thought to be A. hygrometricus were renamed in the 2000s once phylogenetic analyses revealed they were unique Astraeus species, including A. asiaticus and A. odoratus.

Similarly, in 2013, North American populations were divided into A. pteridis, A. morganii, and A. smithii on the basis of molecular phylogenetics.

This research suggests that the type specimen of Astraeus hygrometricus originates in a population restricted to Europe between Southern France and Turkey, with A. telleriae found nearby in Spain and Greece.

[15] Studies in the 2000s showed that several species from Asian collection sites labelled under the specific epithet hygrometricus were actually considerably variable in a number of macroscopic and microscopic characteristics.

[18][19] A follow-up analysis from 2013 named two new North American species: A. morganii from the Southern US and Mexico and A. smithii from the Central and Northern United States, and grouped western US specimens in A.

[19] Young specimens of A. hygrometricus have roughly spherical fruit bodies that typically start their development partially embedded in the substrate.

This simultaneously pushes the fruit body above ground to reveal a round spore case enclosed in a thin papery endoperidium.

[23] This adaptation enables the fruit body to disperse spores at times of optimum moisture, and reduce evaporation during dry periods.

[24][25] Further, dry fruit bodies with the rays curled up may be readily blown about by the wind, allowing them to scatter spores from the pore as they roll.

[26] The exoperidium is thick, and the rays are typically areolate (divided into small areas by cracks and crevices) on the upper surface,[27] and are dark grey to black.

[11] The use of scanning electron microscopy has shown that the spines are 0.90–1.45 μm long, rounded at the tip, narrow, tapered, and sometime joined at the top.

[16] The capillitia (masses of thread-like sterile fibers dispersed among the spores) are branched, 3.5–6.5 μm in diameter, and hyaline (translucent).

The threads of the capillitia arise from the inner surface of the peridium, and are thick-walled, long, interwoven, and branched, measuring 3–5.5 μm thick.

[41] A study of a closely related southeast Asian Astraeus species concluded that the fungus contained an abundance of volatile eight-carbon compounds (including 1-octanol, 1-octen-3-ol, and 1-octen-3-one) that imparted a "mushroom-like, earthy, and pungent odor that was evident as an oily and moss-like smell upon opening the caps".

[16][18] Although A. hygrometricus bears a superficial resemblance to members of the "true earthstars" Geastrum, it may be readily differentiated from most by the hygroscopic nature of its rays.

[26] Unlike Geastrum, the young fruit bodies of A. hygrometricus do not have a columella (sterile tissue in the gleba, at the base of the spore sac).

[43] Geastrum tends to have its spore sac opening surrounded by a peristome or a disc, in contrast with the single lacerate slit of A. hygrometricus.

There are also several microscopic differences: in A. hygrometricus, the basidia are not arranged in parallel columns, the spores are larger, and the threads of the capillitia are branched and continuous with the hyphae of the peridium.

[38] The false earthstar is found on the ground in open fields, often scattered or in groups, especially in nutrient-poor, sandy or loamy soils.

[31] Gelatinipulvinella astraeicola is a leotiaceous fungus with minute, gelatinous, pulvinate (cushion-shaped) apothecia, known to grow only on the inner surface of the rays of dead Astraeus species, including A. hygrometricus.

The compounds, named astrahygrol, 3-epi-astrahygrol, and astrahygrone (3-oxo-25S-lanost-8-eno-26,22-lactone), have δ-lactone (a six-membered ring) in the side chain—a chemical feature previously unknown in the basidiomycetes.

[60] Studies with mouse models have also demonstrated hepatoprotective (liver-protecting) ability, possibly by restoring diminished levels of the antioxidant enzymes superoxide dismutase and catalase caused by experimental exposure to the liver-damaging chemical carbon tetrachloride.

[61] This earthstar has been used in traditional Chinese medicine as a hemostatic agent; the spore dust is applied externally to stop wound bleeding and reduce chilblains.