On a cold Wednesday morning in mid-April, New Yorkers awake to a dusting of snow covering the tulips and narcissi already late to bloom after an unusually long winter. Marie Viljoen is about to leave her Harlem apartment to collect some food for a dinner party she is hosting this Friday evening. She's not on her way to the market, but to Inwood Hill Park, an old forest in northern Manhattan. "I'm going foraging in the snow!" she says in her lilting South African accent, laughing.

Viljoen (pronounced fill-YOON) scrapes a small carbon steel knife along a sharpener, then stashes the knife—used to cut the stems of edible plants and mushrooms—in her backpack. She adds her subway card, paper towels, and paper bags for gathering vegetation, because "plastic makes plants sweat." Despite the snowfall, she feels hopeful. She guided a foraging tour in the park a few weeks earlier and found some field garlic and mustard greens.

Viljoen is not alone in her effort to harvest wild food in New York City. Despite its reputation as a concrete jungle, seemingly inhospitable to plant-life, let alone anything worthy of being eaten, New York supports a healthy underground foraging culture. Unofficial tour groups and individuals canvass the city parks and green spaces in search of edible vegetation, and numerous foraging blogs catalog people's latest finds.

Roughly 20 percent of the city's population forages, estimates Marla Emery, a researcher with the US Forest Service who, along with Dr. Patrick Hurley, investigates foraging in urban environments. "That encompasses everyone like Marie, who are very focused and who dedicate a lot of time to foraging, and people who take a hike and pop a few berries into their mouth," Emery says.

In this light, New York City becomes a virtual salad bar, with Viljoen one of the eager diners who hope to inspire more people to come eat.

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Marie Viljoen (Regan Penaluna)

A few weeks earlier, on a rainy day at Inwood Hill Park, a group of eight hover around Viljoen, who wears a white winter cap over her auburn hair. They've paid her $30 a piece to reveal the gustatory delights hidden right underfoot. Umbrella in one bare hand, she uses her other to yank a fistful of bright green plants from the wet ground.

"If you don't want to get dirty, now is the time to put on your gloves," she says, separating one plant and passing it around. It has the rubbery tube of a chive and the bulb of a garlic clove. It's field garlic, which smells and tastes like a mild version of its store-bought cousin. Now is the best time of year to harvest it because the bulbs are firm. "Friends and I will come out and spend an hour collecting large groups of it," she says. She likes to bake it into cheese bread and mix it into salted butter.

"This, however, is probably poison ivy," she laughs, pointing to a leafless twig at her heel. "It's hard to detect this time of year, because it does not have its distinctive three leaves."

With Viljoen's knowing eye, the early spring landscape transforms from lifeless brown into a vibrant world of budding vegetable life and history. But how this South African came to be an expert on foraging in New York City is itself a story of transformation.

She grew up in Free State, South Africa. Her mother, an actress and amateur botanist, grew vegetables, fruits and herbs, and her father took her foraging. Her parents also let her explore on her own, she recalls, though she was "a young white girl roaming alone during Apartheid."

At eight, she was riding her teal green bicycle beyond the grassy hill in front of her house, filling a basket with berries and plants that she would eat indiscriminately. "I was quite lucky that they were edible," she laughs. Four years later, her family moved to more cosmopolitan Cape Town, where Viljoen and her mother enjoyed hiking into the hills just outside of the city, foraging for milk cap mushrooms.

In 1994, Viljoen moved to the U.S. to pursue a career as an opera singer. But a few years later, an encounter on the 6 train in New York City changed her plans. She sat next to a young boy who had a vigorous cough. She, too, developed a hoarse cough. As a teen, she had failed to get her booster vaccination against whooping cough; the disease transformed her voice and ended her opera career. "It was a definite fork in the road," she says.

For a new career, she turned to what was familiar, and started designing gardens for city dwellers. Then in June, 2007, a friend brought her a branch of berries from a city park. When Viljoen bit into the fruit, it had a blueberry texture and the sweetness of an apple.

"That opened my eyes that there are things in New York City that are good to eat," she says. "This was very exciting."

After looking up its name, "service berry," her obsession began. To learn more about local plants that were safe to eat, she went on foraging tours, read local guides and contacted those more knowledgeable. Seven years later, she runs a gardening and foraging blog called 66 Square Feet (the size of her former garden), gives frequent foraging tours in various city parks and writes about foraging for Edible Manhattan and Brooklyn.

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Foraging tools (Regan Penaluna)

On the tour in Inwood Hill Park, the rain continues, but Viljoen pushes on. She stops and excitedly cuts a branch from what looks like a tall, lifeless shrub. It's spicebush, and the freshly chopped branch smells like citrus and pine. Its twigs can be steeped in hot water for tea, and in season, she harvests its berries to flavor pork roast, cookies and cake.

Just then, a white Parks Department van drives by. She hides her knife behind her back. "Please don't arrest us!" she laughs nervously, waving at the driver.

It is against park rules to "mutilate, kill or remove from the ground any plants, flowers, shrubs or other vegetation under the jurisdiction of the Department," states Parks Department spokesperson Zachary Feder in an email. "Violators of this rule are subject to fines of $250 per violation."

Viljoen's fear of arrest is not wholly unwarranted. In the 1980s, local forager Steve Brill was arrested while foraging for dandelions in city parks, though the charges were later dropped. Brill continues to give his popular tours through Central Park, Prospect Park, and Inwood Hill Park, and officers rarely bother him now, he says. When they do, he just brushes them off, "sort of like when there is a mosquito."

The Parks Department claims that because most of the park vegetation is planted purposely, foraging them constitutes theft. "Many of the plants that you see in city parks do not grow there wild. They are often grown in greenhouses and transplanted into parks by our gardeners," says Feder.

"Central Park isn't a natural landscape, it's entirely manmade," agrees Dena Libner of the Central Park Conservancy in an email. "When individuals forage in Central Park, they're actively destroying the carefully planned and maintained work of those 200 employees, as well as destroying the experience intended to be shared by 40 million annual visitors."

Viljoen herself has never been stopped, and she disagrees with the Parks Department's approach. "There is a perception that if you are doing a tour you are going to denude the entire park of plants," she says. But she's careful to only pick what administrators consider "weeds" or plants that will easily grow back. Those who practice this sustainable approach to foraging are known as "invasivores," though Viljoen isn't eager to call herself one.

Brill, who started his tours in 1982 and whom Viljoen originally toured with, echoes Viljoen's skepticism that mass foraging destroys parks. "I teach thousands of people every year. I have had over 80 people on a tour in Central Park, and it hasn't happened yet."

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Foraging books (Regan Penaluna)

In fact, fear of being caught is secondary to the fear that haunts all foragers: mistaking a toxic plant for one that's edible. For those starting out, Viljoen recommends first identifying the plant as edible, and then eating a small portion in case of an allergic reaction. She says you should never eat a plant if you do not know what it is. A novice should never eat a mushroom, she warns: one bite of the wrong kind can kill someone.

When she began foraging, one experience scared her husband so much he asked her to swear off foraging altogether. On a hike, she discovered a May apple, a native plant with scrumptious fruit that are toxic when not ripe. She picked a ripe fruit, and enjoyed the tropical flavors until she noticed the many tiny seeds she'd ingested with the flesh and remembered reading that they can carry toxins. She quickly called Brill, who told her to go to the emergency room. In a panic, she made herself throw up everything she'd eaten. She was fine, but reminded of the risks of wild food.

During the tour, Viljoen also identifies plants that are edible, but not necessarily delectable. One is the pine tree, whose needles are full of vitamin C. Most flowers are edible, but flavorless, she says. The grub-infested oyster mushroom yields a lot of protein, if nothing else. "I'm not a survivalist," she says. "I only eat what is delicious."

"It sounds like there's two kinds of foragers, survivalists and those that like food," says Anita Kishore, a self-described New York City foodie who's on the tour. "Yes, some are preparing for Armageddon," says Viljoen. "There is a clear line between people who eat for culinary adventure and those who do it for existence." She's clearly in the former camp.

"She lives to be pleased, to enjoy the beauty of the natural world," says her friend Mimi Hoang. "And of course food. Everything she does in that regard is absolutely perfect and very well-thought out." Hoang gave an example of a picnic with Viljoen."She abhors Tupperware and paper plates," says Hoang. So Viljoen used real silverware, tin plates and beautiful linens. "She just really loves things that look beautiful and taste amazing."

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A partially foraged meal (Regan Penaluna)

Two days after her snowy foraging trip, Viljoen has set the table with mismatched china, a vase of tulips, and candles. Outdoors, it's another unseasonably cold evening. Inside, the oven quickly heats the one-bedroom apartment, and the candles glow.

This morning, she emailed guests with tonight's menu, and warned them to "come hungry." Her snowy Wednesday excursion was a success, and she filled her bag with the asparagus-like Japanese knot weed, fistfuls of wild garlic, clumps of toothed-leafed garlic mustard and a lone dandelion. All of these plants the Parks Department calls weeds and spends money to exterminate. Viljoen removed some for free and will feature them in tonight's meal.

Her friends, local foragers and their partners, arrive, and Viljoen immediately serves deviled eggs with field garlic, and what she half-jokingly calls "weed bruschetta:" toasted homemade sourdough bread topped with sautéed and bitter tasting nettle, dock and field garlic greens. The discussion ranges across many topics, including the large amount of mushrooms Gary Lincoff, a local mycologist and minor celebrity in foraging circles, identified this spring. "It's going to be a good year for mushrooms," muses Laura Silverman, the author of the blog Glutton for Life.

The guests move to the table for the first course. Japanese knotweed, an invasive species, can be found in New York parks and in ditches along highways. Tonight Viljoen has pureed it into a soup with a thick, nutty flavor. Guests call it a wonderful complement to the cold weather outside.

Then Viljoen dishes up a decadent chicken liver pate mousse covered with field garlic chutney, followed by a steaming schwarma-style lamb and potatoes, both flavored with buttery field garlic and salt. For dessert she serves a spicebush-infused crème brulee. Her guests leave near midnight, sated and inspired.

Viljoen has many plans. She is finishing a recipe book for wild plants, and is considering teaming up with chefs to create a dinner series based on wild foods. Even though she's ambitious, what counts as a victory isn't professional recognition, ultimately.

She recounts a soup she made for her husband recently that included foraged ramps and Japanese knotweed from the Catskills. "Honestly, that bowl of soup was one of the best things I've ever eaten. Everything in the soup was seasonal," she says. "To me, something as fleeting as that is a triumph."

Regan Penaluna's writing has appeared in The Chronicle of Higher Education, The Philosophers' Magazine, and The Brooklyn Ink. She is writing a book about two 17th-century women who became philosophers when females were banned from universities. She lives in Brooklyn.