We placed two oaks early this year, and bedded around them with cypress mulch. They are both healthy, but from the mulch there is emerging some species of fungus...toadstool?...mushroom?...that is dark brown to black, knobby round and about half to full size of a golfball. Anyone know what it is? Anyone know whether it might be harmful to the trees in any way? the trees are both about 9 inches in diameter at the base and maybe 18-20 feet tall.