Yep...it is a type if fungus. This poses no problems other than looking a bit odd.
More than likely mold - if it has been damp / humid we get it too. Sort of has a hard 'shell' or crust too it. Sometimes orange or reddish
Fungus - we had tons of toadstools come up all over our garden which was heavily mulched after 2 solid weeks of heavy downpours. If this is not growing anywhere near the house ie. not in garden beds that abut the house walls, then I would not worry about it. If it is growing in flower beds abutting the walls of the house then I would not be mulching those areas as it would appear they retain water as it is - hence the mould/fungus growth. Poor drainage in flower beds abutting house walls can cause damp and insect problems for your home.
do you have a bigger picture? or do you know how it looks underneath? some of these mushrooms could be even edible :) really!
It is def a fungus. If you have a dog, make sure he/she doesn't eat them. I have a friend who's dog ate some on her property and nearly died. I have tons on my property and some of them are like puff balls. When I pop them they emit a dust which I am sure means I will get many more lol. Don't try eating them yourself (which I am sure you know). Many are highly poisonous and could either kill you or take you on quite a trip.
It is called dog vomit slime mold. I had it for the first time on some decaying wood chips on some landscaping next to my house this year. It does spread by spores, so don't spray it with water, which is exactly what I did because I thought it was.......dog vomit, duh. It thrives in warm, humid settings of decaying vegetation, particularly leaves and wood chips. It is basically harmless and to get rid of it, just pick it up with your hand in a plastic bag, turn the bag inside out over the top of it and toss it. Or leave it unless it's interfering with food plant growth. Do a google search. Lots of diff. types.
check this out: http://en.wikipedia.org/wiki/Suillus_grevillei. there are lots of types of this mushroom. put the name and google and see if your mushroom is similar. if that what it is, it doesn't do any harm. not all fungus is bad.