Ophiostoma ulmi is a species of fungus in the family Ophiostomataceae. It is one of the causative agents of Dutch elm disease. It was first described under the name Graphium ulmi, and later transferred to the genus Ophiostoma. Ophiostoma ulmi was the first known cause of Dutch elm disease . Since its discovery in 1910, new forms of the fungus, specifically Ophiostoma novo-ulmi, have emerged and appear to be more resistant to control measures and more aggressive in their infection.