DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
A witches' broom on a Hornbeam tree, Carpinus betulus, growing in Ashwellthorpe Wood, an ancient woodland in Norfolk UK, photographed in April. Witches' brooms are galls, consisting of a mass of small twigs arising, here, from infection by the Ascomycete fungus Taphrina carpini. The reproductive structures of the fungus (asci ) are produced in spring as the twigs of the witches' broom come into leaf. These leaves are stunted in growth and do not persist, and the presence of the infection does not seriously affect the growth or reproduction of the tree itself.
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