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