Shelf fungus

I told you that mushrooms were popping up in the back yard. Those mushrooms had a stem and a cap on top.
It's still raining. Mushrooms are still popping up.

Here's a different kind of mushroom:

These mushrooms look as if they are growing straight out of the fallen limb. They don't have separate stems or caps.

Why are they growing there?

They are helping the wood decay.