It’s a fungus/mushroom growing on the Decomposing woody mulch/shredded wood. Not sure what kind. Obviously don’t try to eat and wash hands after handling just to be careful. In most cases though, fungus growing in bagged stuff are harmless unless — even intentionally seeded for better wood decomposition and added healthy soil — unless you Have specific mold or spore allergies.
Typically, fungi will shrivel and die in the sun. Mix up the material to break up the white network of mycelial growth (“roots”)
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