Oak mazegill 
Oak-loving Gymnopus 
Oak-stump bonnet cap 
Oakbug Milkcap 
Oakman Ringless Amanita 
Ochre Spreading Tooth 
Ochre-gilled barefoot lepidella 
Octopus Stinkhorn 
Old man of the woods 
Old Potato Amanita 
olive-capped suillus 
Omphalina pyxidata 
Onion Earthball 
Onion-stalk Parasol 
Onnia subtriquetra 
Orange Birch Bolete 
Orange bonnet 
Orange Coral 
Orange Gilled Waxcap 
Orange milkcap 
Orange Moss Agaric 
Orange mycena 
Orange Oak Bolete 
Orange oyster