I was at a client's property the other day and ran across the unique looking Grifola frondosa fungus - commonly called Hen of the Woods (check out the similarity).
Hen of the Woods often attaches to the roots of Oaks, which was exactly the case with the specimens I saw. Unfortunately, this cool looking fungus is a parasite that extracts nutrients from a tree's root system and tends to cause root and butt rot (decaying the tree from the bottom and rising as time progresses). In the urban forest, this can quickly lead to a hazardous tree situation. Fungi are often indicators of poor tree health, so if you see one, it's wise not to ignore it.