C. nigra may refer to:
Animals Cardiocondyla nigra, an ant species in the genus Cardiocondyla Ciconia nigra, a large wading bird species Coracopsis nigra, a black coloured parrot species native to Comoros, Madagascar, Mayotte and Seychelles Chelonoidis niger, the largest living species of tortoise, often historically misspelled as "nigra"
Plants Carex nigra, a perennial plant species native to wetlands of Europe and Siberia Crataegus nigra, a hawthorn species Centaurea nigra, a flowering plant species
See also Nigra (disambiguation)