Witches broom or little leaf disease is usually a hormone-induced growth distortion of woody plants that only affects part of the plant.
In a prior Foxypress I discussed galls that differ from the strange and miniature witches broom shoots and leaves, which are induced by insect spread viruses and phytoplasma (primitive bacteria), or fungal infection.
The image on the left shows a wandoo affected by witch's broom near the Marri picnic area.
Fasciation is an associated disorder that causes strange strap-like flattening of growing points and flowers. Images below are on canola and an isopogon.
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Images below show a type of witches broom caused by A rust fungus Ceratacoma jacksoniae that affects a range of pea flowers. Images show an infection on stinkwood (Jacksonia epiphyllum). The strange red growths contain tiny reddish fruiting rods that are quite different from the powdery rust pustules that occur on our crops.
 witches broom on stinkwood |  strange growths containing the fruiting bodies |  rod-like fruiting bodies |