Thanks once again to Robert Klips (Orthotrichum@Flickr) for sharing one of his photograph with BPotD (original via the BPotD Flickr Pool). Much appreciated!
Though these may appear to be acorns rapidly fired into small bits of cookie dough, they are actually the fruiting bodies of the rounded earthstar, Geastrum saccatum. Geastrum literally translates to earth star, and the genus has a cosmopolitan temperate and tropical distribution. Geastrum saccatum contributes to that broad range, as it is the most widespread species.
As Robert explains in his comments on Flickr, earthstars resemble puffballs when the fruiting bodies first begin to develop. As it matures, the outer skin (outer peridium) splits and peels back, forming the star pattern. In some species, the shape and length of the segments of the outer peridium are enough to elevate the inner spore sac away from the ground, but in the case of Geastrum saccatum, the fruiting body remains relatively flat and close to the ground (or as Michael Kuo describes in a linked article above, the spore case "sits directly on the arms, as though in a bowl (without a pedestal)".
Geastrum saccatum is a saprobe, gaining its nutrients from dead or decaying organic matter.
No, it"s not edible.
Posted by: Daniel Mosquin Source