Abstract
To date, five species of Ceratolejeunea are known from the East African Islands: C. belangeriana and C. calabariensis from a number of localities, C. variabilis from three, and C. papulifl ora and C. umbonata from single stations. This paper newly establishes the synonymy of C. calabariensis with the Neotropical C. cornuta and of C. stictophylla with C. papuliflora, and reports several additional localities of the latter species. Ceratolejeunea diversicornua, previously known from West Africa only, is reported from Madagascar, and C. andringitrae and C. saroltae are described as new to science. A key to the species of Ceratolejeunea from the Indian Ocean Islands is provided. The taxonomic position of C. boschiana remains uncertain.