'Shrooms

We have a Japanese Maple Tree that lives in a pot in our living room.  It's deciduous, and therefore has no leaves at the moment, but as far as I can tell the bare tree is still alive.  Recently, however, we noticed some strange growth at the base of the tree...

Apparently, we have started our own little mushroom farm without even trying!  :)

I've done some reading, and its apparently not uncommon to have mushrooms show up in a plant pot - the spores likely came in with the plant, and showed up now that it lives right next to the radiator, and gets regular water.   Now I just have to figure out what kind of mushrooms they are, so I'll know how careful I'll need to be when curious children and/or pets come over to visit!  :)