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.

Dutch elm disease originated in Europe in the early 1900s. Elm trees were once an ecologically valuable tree that dominated mixed broadleaf forests, floodplains, and low areas near rivers and streams. They were planted in urban settings because of their aesthetic appeal and their ability to provide shade due to their V like shape. An outbreak of Dutch elm disease in the 1920s and again in the 1970s was responsible for the death of more than 40 million American elm trees.

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.

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