A new marine Ascomycete,Caryosporella rhizophorae Kohlm. gen. et sp. nov., is described from dead wood of intertidal roots and branches ofrhizophora mangle growing on three small islands off the coast of Belize (Central America). The new genus is compared withCaryospora, and its placement in the Melanommatales and Massariaceae is discussed. The new species is considered to be an obligate marine fungus, but because of its taxonomic position it belongs to the group of secondary marine fungi that originated from terrestrial ancestors.