With about 100,000 known species of fungus that live in or on the soil, most take the form of mushrooms, molds, mildews, rusts, truffles, stinkhorns and puffballs. Scientists discover new species of fungus each year. The way the fungus affects the soil is a particular concern to gardeners and farmers.
Some species of earth stars were discovered as early as 1688. Some, such as the Geastrum fornicatum, are easily identifiable because of their shape--similar to a human figure. The fungus' outer wall is leathery and splits open, so that the body appears to have legs. These legs support the spore case and attach themselves to leaf debris.
There are several subspecies of stinkhorn, including the Phallaceae (phallus-like stinkhorns), a variety that smells foul and attracts flies. This fungus begins as a small body in the soil, then grows into an egg-shaped form about the size of a golf ball. The stalk then breaks through the egg and forms a basal volva, shaped like a cup, as the stalk gets longer. A putrid, black mass of spore slime covers the cap or head of the stalk, and causes an unpleasant odor. One variety of stinkhorn, called the net stinkhorn or bamboo fungus, is dried and sold in Asia. The dried fungus is simmered in water until it is tender, then served in vegetarian cuisine.
The Armillaria bulbosa is a soil fungus that spreads over large areas rapidly. One Armillaria bulbosa covers more than 30 acres of soil in northern Michigan. According to Wayne's World at Paolomar.edu, it is one of the world's largest living organisms. Another type of Armillaria has a subterranean mycelial network, connected by common roots, covering the Rocky Mountains. According to Wayne's World, it is not known if this particular strain is a single organism, connected by the underground roots, or if is it many different organisms that connected their roots, forming one large covering.
Truffles are the ascocarps, or fruiting bodies, of the mycorrhizal ascomycetous fungus. They live underground and look like small pebbles under the soil. Truffles are 1 to 2 centimeters wide. They do not depend on the wind to spread, rather they spread by animals that eat them via spores that pass through the animals' digestive tract. They are harvested with a rake--if you can get to them before pigs and dogs. Bear cubs in Russia also sniff out and eat truffles, as do goats in Sardinia. Truffles emit the chemical androstenol, which gives the truffle its odor. The same odor is found in men's underarm perspiration and in women's urine. The chemical has also been added to some cosmetics.