Toadstool, Mushroom or Fairy Ring
Toadstool is the slang term for mushrooms. Toadstools are simply the interesting looking fruiting bodies of fungi working to break down organic matter in the soil. The organic matter being eaten can be compost, mulch, old lumber but is more commonly dead and decaying tree roots. These saprophytic fungi are not harmful in any way, but can be eliminated by kicking over or spraying them with baking soda or potassium bicarbonate at about 1 rounded tablespoon per gallon of water.
Cornmeal juice will also control them for a while. These decomposers will grow back until the organic matter is completely broken down.
There are three good books on these helpful organisms:
Mycelium Running - How Mushrooms Can Save the World
by Paul Stamets, Ten Speed Press.
Edible Wild Mushrooms of North America
by David W. Fisher and Alan E. Bessette, University of Texas Press.
Edible and Poisonous Mushrooms of the World by Hall, Stephenson, Buchanan, Yun and Cole, Timber Press.
More information at these websites: