About 50; See text Geastrum (orthographical variant Geaster)[1] is a genus of puffball-like mushrooms in the family Geastraceae.

At maturity, the outer layer of the fruiting body splits into segments which turn outward creating a star-like pattern on the ground.

In some species, the outer peridium splits from a middle layer, causing the spore sac to arch off the ground.

The mouth in most species of "earth-stars" is quite prominent, often arising as a small cone at the apex of the inner peridium.

[5] Some similar species that are otherwise difficult to differentiate using classical morphological features (such as G. triplex, G. saccatum, and G. lageniforme) can be identified using chemical spot tests that detect phenoloxidase enzymatic activity, a differences in the crystal structure of calcium oxalate deposits[6] or DNA sequences.