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)
For the Witch's Broom Nebula
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-broom disease caused by phytoplasmas is economically important in a number of crop plants, including the cocoa tree Theobroma cacao,
jujube (Ziziphus jujuba) and the timber tree Melia azedarach.