Some photographs of Armillaria (honey mushroom) underneath the bark of a dead tree. The rhizomorphs look like plant roots but they are filled with hyphae, which sometimes emerge in a more classical mycelial fan. If you find these in your backyard, look for bioluminescence on a cloudy, moonless night. Just give your eyes about 20 minutes to acclimate.
Here’s the fruiting body, photographed at a different location: