ABSTRACTA new species,Ceratocystiopsis proteae, collected from insect-infestedProtea repensis described.Knoxdaviesia, a new genus of dematiaceous hyphomycetes is described to accommodate the anamorph ofC. proteae. Ceratocystiopsis proteaeshares characteristics ofCeratocystis sensu stricto(cycloheximide sensitivity),Ceratocystiopsis(falcate ascopores) andOphiostoma(relatively long perithecial necks, divergent ostiolar hyphae and an anamorph with holoblastic conidium development) but is currently best accommodated inCeratocystiopsis. Knoxdaviesia proteaesuperficially resembles the hyphomycete generaLeptographiumandStachybotrys.This is the first species of Ophiostomataceae described from an indigenous plant in southern Africa and its relationship with other Ophiostomataceae is discussed.