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This is part of a cedar tree, but what is that strange brown thing? It is a rust gall! Cedar-Apple Rust is a type of fungus, and a gall refers to that growth. It lives on trees, wrapping around branches and leaves. In spring, the gall extrudes a gelatinous mess when wet. This contains its spores (seen in the second picture). Rust doesn’t generally kill a tree, but it is rather unsightly, and in fruit trees it can ruin fruit.

Photo Sources: Brilliant Botany, x