HI, I have had the attached fungus? in different patched in my rather airy greenhouse last year, I am wondering if you know what it is?
It is not uncommon for unusual fungi to appear in the warmth and dampness of a tunnel. This looks like a plaster fungus, growing probably on organic matter in the soil. These are decomposing fungi, part of the cycle of nutrient release, and not generally harmful to plants. A bit unsightly maybe but no harm.