| Host genus | Fungal species | Symptoms and notes |
| Calamagrostis | Claviceps purpurea | The ergot fungus, infecting inflorescences and forming sclerotia from modified seeds. Highly toxic |
| Calamintha | Puccinia menthae | Rust of leaves and stems |
| Callistemon | Allelochaeta dilophospora | On leaf spots and died-back areas of living leaves |
| Caltha | Puccinia calthicola | Rust on leaves and petioles |
| Camellia | Alternaria camelliae | Associated with conspicuous white leaf spots |
| Carex | Anthracoidea limosa | An inflorescence smut of Carex limosa, probably causing little damage to host populations |
| Gaeumannomyces caricis | Parasitic, but pathogenicity needs confirmation | |
| Gaeumannomyces paludosus | Parasitic, but pathogenicity needs confirmation | |
| Puccinia magnusii | Rust on leaves of Carex riparia | |
| Puccinia ribesii-pendulae | Rust of leaves of Carex pendula | |
| Puccinia ribis-nigri-paniculatae | Rust on leaves of Carex paniculata | |
| Puccinia urticae-inflatae | Rust on leaves of Carex rostrata | |
| Carpinus | Mamiania fimbriata | Apparently a weak parasite causing leaf spots in late summer |
| Castanea | Cryphonectria radicalis | A weak parasite causing canker symptoms. Almost certainly extinct in GB&I |
| Centaurea | Puccinia calcitrapae | Rust of leaves and stems |
| Centaurium | Taeniolina centaurii | Probably a necrotrophic pathogen of leaves and stems, but nutritional status uncertain |
| Centranthus | Ramularia centranthi | Causes leaf spots |
| Cicuta | Puccinia cicutae | A rust on leaves and other plant parts, not causing major damage |
| Cirsium | Puccinia punctiformis | A rust of leaves and stems, causing stunting and sterility |
| Cladium | Puccinia cladii | A biotrophic leaf parasite, not considered to be a significant pathogen |
| Clinopodium | Puccinia menthae | Rust of leaves and stems |
| Colchicum | Urocystis colchici | A leaf smut of Colchicum autumnale, not causing significant economic damage |
| Convolvulus | Erysiphe convolvuli | Powdery mildew of leaves |
| Cornus | Septoria cornina | Causes conspicuous leaf spots, similar to those of Sphaerulina cornicola |
| Sphaerulina cornicola | Causes conspicuous leaf spots | |
| Corylus | Asteroma coryli | Causes conspicuous spots on leaves |
| Mamianiella coryli | Considered to cause leaf spotting, but not economically important |