Hymenoscyphus fraxineus
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Hymenoscyphus fraxineus is an ascomycete fungus that causes ash dieback, a chronic fungal disease of ash trees in Europe characterised by leaf loss and crown dieback in infected trees. The fungus was first scientifically described in 2006 under the name Chalara fraxinea. Four years later it was discovered that Chalara fraxinea is the asexual (anamorphic) stage of a fungus that was subsequently named Hymenoscyphus pseudoalbidus and then renamed as Hymenoscyphus fraxineus.
Crown dieback in a mature ash tree
Yellow to red-brown necrosis in a five-year-old ash tree
Wilting of leaves caused by necrosis of the rachis (stem)
Fraxinus americana
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Fraxinus americana, the white ash or American ash, is a fast-growing species of ash tree native to eastern and central North America.
Autumn foliage
Detail of Fraxinus americana twig. The C-shaped leaf scars of white ash are useful in distinguishing this species from the closely related green ash (Fraxinus pennsylvanica). The lateral buds of F. pennsylvanica share a less curved margin with their corresponding leaf scars, imparting an overall D-shape to the latter.
Fall, Russell County, Virginia