This earthstar is also called the “false earthstar,” due to the fact that it belongs to the family Astraeaceae, rather than the family of true earthstars, Geastrum. Although it outwardly resembles a true earthstar, and indeed was grouped there until 1889, it has several differences. Among other things, it has larger spores, no organized hymenium (The spore-producing “substrate” tissue), and it lacks a columella (the sterile section of the spore-producing structure). The new genus Astraeus was originally thought to contain only two species; later analysis revealed six distinct species spread all over the world.
As in most fungi, the identifiable part that we see is only the fruiting body. The real “body” of a fungi is its mycelium, the underground complex of fibrous, branching hyphae. Thus, picking a mushroom (or earthstar) does not harm the organism the way picking a small plant would. The fruiting body of this earthstar is usually around 5 cm across. It is a lighter brown, while the rays are darker.
The young fruiting body of a Barometer Earthstar is a round sac partially embedded in the soil. As it matures, the exoperidium (outer skin) breaks open into numerous rays in a star-shaped pattern. As they split apart, they reveal the spherical spore sac, enclosed in the endoperidium (inner skin). The rays unfold, pushing the spore sac into the air where the spores can be spread. Sometimes, they push it up hard enough to break its connection to the mycelium.