A massed proliferation of the branches of a woody plant. an abnormal proliferation of shoots. A single shoot may be replaced by a large number of shoots; if they all grow in one direction they give the appearance of a broom, but frequently in trees there is irregular orientation and loss of apical dominance, giving an interwoven cluster of shoots which resembles a bird's nest rather than a broom, e.g. that caused by Taphrina betulina in birch trees. The same term is less suitably applied to diseased conditions in herbaceous plants, characterised by increased branching, production of large numbers of slender shoots and often by much reduced leaves, e.g. witches' broom of potato; cf. fasciation. Abnormal, brushlike development of many weak shoots.
Symptoms of abnormal, massed, brush-like development of shoots or roots, mainly on woody plants.