"Wildman" Steve Brill—self-proclaimed as "New York's best-known naturalist," edible-plant expert, and vegan-cookbook author-is entertaining 2-year-old Adeline by clapping his cupped hands in front of his open mouth; we are waiting for our group of 12 to assemble for a Sunday afternoon of foraging in Brooklyn's Prospect Park. By changing the shape of his lips as he claps, Brill produces an impressive range of notes; he does not stint on his rendition of "Pop Goes the Weasel." As he moves out of the minor key bridge of the song to the recapitulation of the initial verse, Adeline's attention has shifted. Then again, so has Brill's. He seems to have entered a minor fugue state, eyes focusing upward, his expression dreamy and beatific. He appears almost saint like, absent the wicker pith helmet and cargo pants. The entire day will see Brill vacillate between just such moments of earnest concentration and the relentless joking of a master schticktician. When we are all gathered, Brill cries, "Walk this way!" And sure enough, he's off, John Cleese-ing across Grand Army Plaza and into the park.

There's no dawdling. Steve Brill is a busy man. His schedule for March through December shows him leading 91 such expeditions in 39 different locations throughout the tri-state area. Today's group of foragers includes a Brooklyn couple and their young son; a venture capitalist who runs a nonprofit theater program for inner-city youth; two teachers from upstate, pen-pals from an online Christian prayer forum who are meeting for the first time; a bleach-blonde Deborah Harry type with pink eye shadow and pink rhinestone cat's-eye glasses, who assists in cooking classes at New York's Natural Gourmet Cookery School; and her boyfriend, whose T-shirt reads GATEWAYS OF ANNIHILATION.

We take leave of the more manicured parts of Prospect Park almost immediately-stopping briefly along the way to sample both hedge mustard and violet leaves (chlorophyll will be one of the overriding flavors of the day). We find ourselves at the edge of a forested area. There, we munch on the parsley-ish leaves of the goutweed plant, named not for the disease but as a bastardization of "goat," the primary consumer of same. (Chickweed is apparently similarly named for the animal that historically liked it best.) By now we are fully into the wooded underbrush, a co-ed dozen led by a chattering docent dressed like Dr. Livingston. The Parks Department unofficially condones what Brill does, although individual rangers may not, so we are advised to be discreet. We pass by many men, alone and in pairs, who don't appear too thrilled by our presence. Discretion is the watchword all around us, clearly; judging from the cellophane crackle underfoot, the condom wrappers are in bloom.

We're not as out of place as we think. Brill began the tour by telling us that flowers were once thought to have no purpose greater than pleasing the human eye. It wasn't until experiments in pollination during the Renaissance that people realized-to their puritanical horror-that even the loveliest of blooms was nothing more than a sexual organ. Linnaeus's books were burned as a result. So who can blame the human fauna for throbbing in concert with the priapic flora in this Brooklyn cruising ground?

It doesn't seem to bother Brill one bit as he leads us through to the next find, one of his favorites: pokeweed. It resembles a stalky romaine. But what initially seems like a consequence-free windfall can become quite confusing in short order. Pokeweed, for example, requires three separate boilings to rid it of its toxins. The big-ticket find of the day is some Wine-cap stropharia mushrooms, apparently delicious. I get nervous that I've somehow managed to harvest the slender-stemmed poisonous fungi that were growing nearby. Later, like the most primitive of animals, I find myself completely drawn in and ready to pick and eat the lovely yellow-bloomed, saffron sapped Greater Celandine bush. It is highly toxic. "Like my ex girlfriend," Brill cracks. "Beautiful but deadly!" (Don't forget to tip your waitress, g'night!) The plant world seems full of traps and false cognates, evil cousins that resemble harmless edibles, just waiting to deliver a lethal dose of neurotoxins. I give my Wine-caps away.

As for Brill himself, he is completely, reassuringly erudite. He describes not only the identifying attributes of each plant as he picks it - leaf shape, distribution, growth pattern, immature versus mature differences in morphology - but also the specific health benefits. Wineberry leaf is very good for women's reproductive health; autumn olive is, pound for pound, far richer in lycopene than tomatoes. He almost always volunteers recipes, as well.

Although by mid May, the pokeweed just past its prime, we manage to pick fair amount. Someone asks Brill if it will grow back. "Of course," he replies. "It's called pokeweed, not poke rare plant." Brill makes a point of harvesting only the most easily regrown and plentiful offerings. I ask him if he ever shops for food. "Occasionally," he says. "I haven't seen too many tofu trees."

There is a seemingly endless supply of food in Prospect Park. By the time we sample delicious cattail, poor man's pepper, and Field Pennycress, we are actually getting quite full. It starts to seem genuinely puzzling, bordering on inconceivable, that the bushes aren't overrun by people harvesting these marvelous free eats. But the tour also proves the opposite point. Even here, we remain subordinate to the realities of the seasons. When Brill finds no more than two eight-inch-long edible stalks left on the Japanese Knotweed tree for the 12 of us, there is no clearer explication of why our ancestors decided to give up gathering and began growing their food some 10,000 years ago. Furthermore, Prospect Park is a vision of Arcadian plenitude, designed as an escape for nearby Brooklynites. Real nature doesn't always result in such a lush array of comestibles, there for the taking. Real nature is not a supermarket. That, alas, is something we had to invent.