plant disorder characterized by a shortening of the internodes and a proliferation of terminal shoots forming a dense. brush-like mass of twigs.

witch's broom (Wikipedia)

Witch's broom or witches' broom is a deformity in a woody plant, typically a tree, where the natural structure of the plant is changed. A dense mass of shoots grows from a single point, with the resulting structure resembling a broom or a bird's nest. It is sometimes caused by pathogens.

Witch's brooms on downy birch, caused by the fungus Taphrina betulina
Witch's broom on a white pine.
Witch's broom in Yamaska National Park, QC

Diseases with symptoms of witches' broom, caused by phytoplasmas or basidiomycetes, are economically important in a number of crop plants, including the cocoa tree Theobroma cacao, jujube (Ziziphus jujuba) and the timber tree Melia azedarach.

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