Mushrooming combines the best of fall -- woodland walks, the chance to bag gourmet vittles in the wild and an element of danger as well as surprise.

"There's the thrill of the hunt, because you don't know what you'll find," said Western Pennsylvania Mushroom Club president John Stuart of Gibsonia. "And I really think part of the allure -- it's always in the back of your mind -- is that some of the most beautiful mushrooms in the forest could kill you if you eat them."

With 5,000 varieties of mushrooms -- the fruiting body of fungi -- growing in Penn's Woods, knowing which to avoid and which to pick requires expert mentoring, Stuart said, and there's no better opportunity to unearth some of the mystery than on Sept. 20 when the club holds its annual Gary Lincoff Mid-Atlantic Mushroom Foray at North Park.

A Squirrel Hill native now living in New York City, Lincoff is a world-renowned mycologist who wrote the "National Audubon Society Field Guide to North American Mushrooms" (Turtleback), and will appear in "Know Your Mushrooms," a Ron Mann documentary film to be released this fall.

Lincoff will lecture and lead forays at the"fungi fest," which also will include a cooking demonstration by chef Tom Chulick of the Backdoor Cafe in Johnstown, and an evening mushroom feast.

"For someone who wants to get a sense of mushrooming in one big lump," said Stuart, "this is it."

Included in the price of admission is a two-year membership in the club, which meets and adventures March through November.

"Most people when they join are thinking about edibles. They like eating mushrooms," said Stuart. "Then when they get into it, they say, 'Gee, they're like little works of art ... Look at the size, the taste, the texture, the smell. Mushrooms appeal to all the senses."

Stuart got into mushrooming after he retired as an opthamologist specializing in corneal transplants.

"I was sitting on a plane next to a woman from Florida who told me she was coming to Pennsylvania to hunt for morels," Stuart said. "I'd had morels in restaurants and thought they were good. I figured, if this woman is flying here to pick them, they must be really special."

Because of its abundant forests, Pennsylvania is a big mushroom state and morels are one of the earliest fruiting species, coinciding with the official start of trout fishing season in mid-April and ending in late May.

"Morels have a wonderful woodsy taste, some people would say nutty," Stuart said. "And you can't cultivate them, although some folks have tried, which is why they're so expensive. If you see them sold, dried, in shops, they've been picked wild, and usually cost about $80 a pound."

This was an especially good year for morels because it was so wet.

"I was finding 50 a day. Some people were finding over 100," Stuart said.

Precipitation is vital to all kinds of mushrooms, which are part of the same biological kingdom as yeast, mildew and mold. Unlike plants, which produce seeds, fungi reproduce by discharging spores, and they don't have roots, only mycelium -- tiny thread-like growths that enable them to feed.

Some mushrooms, such as fairy ring, emerge on lawns, but most grow on living or dead wood or on the ground around tree roots, in symbiotic or parasitic relationships. Many can be typed according to the trees they're near.

"If you can identify trees, you can often predict which mushrooms you'll find when you look down," Lincoff said. "Some are so specific that without a particular tree you'll never see them."

Honey mushrooms, a coveted fall species, grow on various trees, but hen of the woods, another fall favorite, develop only on oak.

You'll see mushrooms only when fungi are deprived of water and nutrients and go into a fruiting period, Lincoff said.

"Some species will fruit in spring, go dormant in summer, and reappear in fall, but most are as seasonal as wildflowers, and you can recognize the time of year by which mushrooms are fruiting."

Mushrooms vary in their potency and appeal. They range from turkey tail, which has shown promise in stemming the spread of cancerous tumors, to the hallucinogenic or "magic" big laughing gym (Gymnopilus), so named for its size and color. Both are found in and around Pittsburgh, Lincoff said.

Only about 20 kinds of mushrooms are choice edibles, including porcini and chanterelle, which also grow in local forests.

"But many more varieties can make people sick and half a dozen can be deadly," Lincoff said.

Some of Penn's Woods' mushrooms are among the most notorious.

"The amanita is responsible for 90 percent of deaths," said Stuart, of a genus that encompasses many kinds of toxic toadstools. "In fact, some amanita are called Death Angel because they look so pristine and beautiful. People who've eaten them and lived to tell the tale say they taste pretty good, too."

Stuart said he read a recent account of a Connecticut man who ate a mushroom he'd picked near a parking lot and died. That makes a good case for joining a group of knowledgeable " 'shroomers," said Stuart. "It really helps to learn from experts."

And interest is, well, mushrooming. In the six years since the Western Pennsylvania club was organized, membership has grown to more than 350, Stuart said.

Lincoff also sees a surge in 'shrooming, and credits supermarkets and TV cooking shows with introducing consumers to species such as the large, brown portobello, which often is touted as vegetarian steak. But what folks may not know is that farm-raised fungi have many wild cousins.

"The button mushroom, which includes the portobello, isn't very different from some of the species we find on lawns, in parks and in woods around Pittsburgh," said Lincoff. "They include pink bottom, spring agaricus, and horse mushroom."