Agaricus xanthodermus (Genevier)  var. lepiotoides (Maire)

I have listed this taxon here because it exists in the literature, but there is no doubt that it does not represent a true biological species. The cracking and lacerations of the cap are purely environmentally driven and as the photo below suggests, the members of the same patch can look quite differently whether exposed directly to the elements or not. The most spectacularly ornamented caps exist in the coastal areas where exposed to a continuous salty breeze.

The picture shows a mixed collection of Agaricus xanthodermus v. xanthodermus and v. lepiotoides -- growing side by side in the same lawn demonstrates that  the cracked cap is not environmentally induced, but the variations are rather distinct.

Macrolepiota rachodes (l) and Agaricus xanthodermus v. lepiotoides (r)