In the Comoro Islands, Rubiaceae are one of the largest families of flowering plants, represented by 33 genera and sixty species. Among these genera, Coptosperma (Pavetteae, Ixoroideae) is represented by two widely distributed species, also occurring in Madagascar and continental Africa, and a third species new to science. Coptosperma mitochondrioides Mouly & De Block possesses large stipules of the "bec de canard" type and ribbed fruits. While this type of stipule is typical for many Malagasy Coptosperma species, ribbed fruits are very rare within the genus. Within the Comoro archipelago C. mitochondrioides is restricted to Mayotte, but the species is also known from northern Madagascar. The new species is described and illustrated and a key to the species of Coptosperma occurring in the Comoros is provided.