Callorina fusarioides – synonym of Calloria neglecta
Calocybe georgii – synonym of Calocybe gambosa
Camarophyllus grossulus – synonym of Omphalina grossula
Camarophyllus niveus – synonym of Hygrocybe virginea
Camarophyllus pratensis var. pratensis – synonym of Hygrocybe pratensis
Camarophyllus russocoriaceus – synonym of Hygrocybe russocoriacea
Cantharellus cibarius var. amethysteus – synonym of Cantharellus amethysteus
Cantharellus lutescens – synonym of Cantharellus aurora
Chlorosplenium aeruginascens – synonym of Chlorociboria aeruginascens
Chroogomphus rutilans rutilus – synonym of Chroogomphus rutilus
Clavaria acuta – synonym of Clavaria falcata
Clavariadelphus fistulosus – synonym of Macrotyphula fistulosa
Clavicorona pyxidata – synonym of Artomyces pyxidatus
Clavulina cristata – synonym of Clavulina coralloides
Collybia cirrhata – synonym of Collybia amanitae
Coprobia granulata – synonym of Cheilymenia granulata
Cordyceps canadensis – synonym of Cordyceps longisegmentis
Cortinarius caerulescens – synonym of Cortinarius coerulescens
Crinipellis stipitaria – synonym of Crinipellis scabellus
Crucibulum laeve – synonym of Crucibulum crucibuliforme
Cystolepiota sistrata – synonym of Cystolepiota seminuda