Coniothyrium cupressacearum (Morelet) Morelet, exhibiting annellated conidiogenous cells in light microscopy, was examined by transmission electron microscopy. Since the conidial wall is formed de novo, i.e. not continuous with a pre-existent layer of the conidiogenous cell wall, the conidiogenesis is clearly phialidic. After production of a number of conidia, a percurrent proliferation of the phialide collar occurs; this explains the annellated appearance. The annellide is not considered to be a special kind of conidiogenous cell but a variation of either the phialide or the aleuriophore.