Macrolepiota gracilenta – synonym of Macrolepiota mastoidea
Macrolepiota rhacodes – synonym of Macrolepiota rachodes
Megacollybia platyphylla – synonym of Megacollybia plathyphylla
Melanoleuca melaleuca – synonym of Melanoleuca polioleuca
Melanophyllum echinatum – synonym of Melanophyllum haematospermum
Melanotus caricicola – synonym of Psilocybe caricicola
Melanotus horizontalis – synonym of Psilocybe horizontalis
Merismodes anomalus – synonym of Merismodes anomala
Merulius corium – synonym of Meruliopsis corium
Mitrophora semilibera – synonym of Morchella semilibera
Mniopetalum globisporum – synonym of Rimbachia arachnoidea
Monilia fructigena – synonym of Sclerotinia fructigena
Monilinia fructigena – synonym of Sclerotinia fructigena
Mycena galopus var. alba – synonym of Mycena galopus
Mycena leucogala – synonym of Mycena galopus
Mycena oortiana – synonym of Mycena arcangeliana
Mycolachnea hemisphaerica – synonym of Humaria hemisphaerica
Myxarium hyalinum – synonym of Myxarium nucleatum