Janet Wynn's dinner guests were in for a surprise. Poking from the evening's salad was wood sorrel, a wild plant that looks like clover and has a tart, lemony taste.

The day before, that same wood sorrel was poking up from the ground about 5 miles from downtown Boston. Wynn picked it during an evening walk along the Charles River led by wild-foods specialist Russ Cohen.

When the evening was over, Wynn had a perfect salad garnish, and Cohen had another convert.

"I loved the walk," the Brookline resident said. "I never knew anything about foraging before this. It's opened up a whole new world for me, and it is right here in our own backyards."

For 35 years, Cohen has been opening up the world of foraging for folks all over New England, giving tours to people interested in free food and picking up a few survival techniques. Lately, he's been pretty busy.

The growing interest, he suspects, springs from a hot trend out of San Francisco that is producing "locavores," people determined to eat only foods picked or produced locally, on a farm or in a forest. He also grudgingly concedes that popular television shows such as "Man vs. Wild" and "Survivor" have given foraging a new cachet.

On a recent sterling evening, Cohen separated fact from fiction in a walk along the Charles sponsored by the Boston chapter of the Appalachian Mountain Club and the Watertown Citizens for Environmental Safety.

The group consisted mostly of young hikers, with a few folks more likely to relate to 1970s cereal commercials by natural-foods proponent Euell Gibbons. Some were mildly curious, others eager, and some, like Wynn, just out for a stroll.

It didn't take long for their attentions to fix on the slightly hippyish man with a close-cropped beard who stopped the procession every few minutes to describe the virtues of plants that looked like, and in many cases were, weeds.

Milkweed, pokeweed, Japanese knotweed. Wild garlic, wild onion, sheep sorrel, European barberry - it makes great jelly - were all found in abundance less than 20 minutes into the walk.

It seemed that the edible far outweighed the inedible, as plant after plant had some leaf, stem, root, fruit, or seed that makes a nice stir-fry, salad green, or seasoning, or tastes just like spinach when steamed.

"Just like many wild animals are said to taste a lot like chicken, a lot of wild plants are supposed to taste just like spinach," Cohen said. "But young mulberry leaves, when you steam them, really do taste just like spinach."

Standing in front of the near-ripe mulberry tree some 20 feet from the river's edge, Cohen dissected its many uses, some of which go beyond nourishment. Not only do the super-sweet ripe mulberries make a great vinaigrette salad dressing, but the unripe fruit is reputed to have recreational properties.

"The raw, unripe fruits are alleged by one wild foods author to be hallucinogenic," Cohen said. "I tried it when I was younger. I didn't experience anything. I don't know, maybe I didn't eat enough."

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