Science magazines
- Cui-ui
- Culebra Island Giant Anole
- Cumberland Bean Pearlymussel
- Cumberland Elktoe
- Cumberland Monkeyface
- Cumberland Pigtoe
- Cumberland Rosemary
- Cumberland Sandwort
- Cumberlandian Combshell
- Curtis' Pearlymussel
- Cushenbury Buckwheat
- Cushenbury Milk-vetch
- Cushenbury Oxytheca
- Cyanea crispa
- Cyanea macrostegia ssp. gibsonii
- Cyanea Superba
- Cyanea Undulata
- Cylindrical Lioplax
- Daphnopsis Hellerana
- Dark Pigtoe