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Hymenoscyphus pseudoalbidus (chalara ash dieback)

Hymenoscyphus pseudoalbidus is a virulent fungal pathogen of ash trees that causes 'chalara ash dieback' in northern and central Europe and has recently spread to the UK.
Hymenoscyphus pseudoalbidus (chalara ash dieback fungus) on twig

Hymenoscyphus pseudoalbidus (Photo: V. Queloz/ETH Zurich, Switzerland)

Species information

Scientific name: 

Hymenoscyphus pseudoalbidus V.Queloz, C.R.Grünig, R.Berndt, T.Kowalski, T.N.Sieber & O.Holdenrieder

Common name: 

chalara ash dieback, European ash dieback, chalara fraxinea, chalara dieback of ash

Conservation status: 

Not assessed.


Dead and dying parts (including twigs and petioles) of European ash (Fraxinus excelsior), narrow-leaved ash (F. angustifolia) and possibly other Fraxinus species.

Key Uses: 

None known.

Known hazards: 

No direct hazards have been reported.


Genus: Hymenoscyphus

About this species

A virulent fungal pathogen of ash trees, Hymenoscyphus pseudoalbidus was first recognized in its asexual form as the cause of dieback of ash trees in Poland. It was originally described as Chalara fraxinea, and this name is frequently used in the popular literature. The origin of the species is not understood in detail, but it seems likely that the fungus was introduced to Europe from eastern Asia.

Hymenoscyphus pseudoalbidus is similar in appearance to H. albidus, a common and widespread species native to Europe, which fruits on dead ash petioles and twigs but does not cause disease. Recent research in Denmark has suggested that H. pseudoalbidus is an aggressive competitor, occupying the same ecological niche as H. albidus, leading to decline of the native fungus.


Chalara fraxinea T.Kowalski


main info

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