'Beach Umbrellas'

This is what's happening to one of my plant pots. I am having what looks like mini toadstools growing.
I always felt that I don't water the plants enough, well, this is certainly one sign that the soil is sufficiently damp and that although we have been experiencing higher temperatures, it's probably very humid.
Has anyone ever wondered why they grow the way they do? Why this particular shape? From what I remember, the spores are on the underside of the top - looks like it's some beach resort scattered with umbrellas.....

Anyway, I think it's pretty.
Should do some research on these things - they are fascinating although I do prefer the ones we see along the roads here sometimes, growing near the trunk base of the tree.....the white ones...which are obviously much larger.