### Identification To spot *Uromycladium morrisii*, commonly known as the Silver Wattle Gall Rust, look for spectacular, distorted woody growths on the branches of *Acacia* trees. These galls are irregularly lobed and rugose, often resembling miniature, charred brains or clusters of chocolate-dusted cauliflower. While its relative *U. tepperianum* forms more globose, singular galls, *U. morrisii* is distinguished by its complex, multi-lobed structures and its specific preference for the Silver Wattle (*Acacia dealbata*). In late winter and spring, the field mark is unmistakable: the gall’s surface becomes velvety, covered in a thick, dusty coating of cinnamon-to-chocolate brown teliospores that will stain your fingers if touched.
### Habitat & Range This fungus is a specialist of the temperate sclerophyll forests and riparian zones of Southeastern Australia, particularly across Victoria, New South Wales, and Tasmania. It is most frequently encountered in damp gullies and along forest edges where its primary hosts, the Silver Wattle and Black Wattle (*Acacia mearnsii*), dominate the mid-story. It has also been introduced to New Zealand, where it follows its host plants into plantation and ornamental settings.
### Behaviour *U. morrisii* acts as a biological architect. Upon infection, the fungus hijacks the tree’s hormonal signaling, forcing the host to divert massive amounts of energy into building the gall. This "hijacking" often results in "witches' brooms"—dense, chaotic clusters of stunted twigs and foliage that sprout near the infection site. An observer will notice that heavily infested trees appear "lumpy" and may show significant dieback, as the fungus outcompetes the tree's own reproductive organs for resources.
### Diet As an obligate biotroph, *U. morrisii* does not "hunt," but rather siphons. It functions as a sophisticated parasite, extending microscopic hyphae into the tree’s vascular system to tap directly into the phloem. It lives entirely off the sugars and water synthesized by the wattle, effectively "eating" the tree's liquid energy to fuel its own spore production.
### Fascinating Fact Each gall is a "micro-metropolis." While the fungus provides the architecture, the woody chambers become high-rise apartments for a staggering variety of invertebrates. Dozens of species of moths, beetles, and gall-wasps move into the structures, using the fungus-built fortress for protection and food, creating a tiny, hidden ecosystem within the distorted branch.