A year ago, Sean Power was traveling in Italy, where he found a street vendor roasting chestnuts. After seeing similar nuts fall from trees...

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A year ago, Sean Power was traveling in Italy, where he found a street vendor roasting chestnuts. After seeing similar nuts fall from trees at Seattle’s Volunteer Park, he looked up some recipes online and set out to re-create his European experience at home.

It wasn’t until Power, who does housing research for the city of Seattle, did a bit more research that he realized the nuts he’d harvested were dangerous. Luckily, that was before he’d bitten into one, but his sources told him the nuts would be very bitter anyway.

“You know how nature will sometimes tip you off?” he says. “They have a horrible taste.”

Evil chestnut impostors are, in a nutshell, making life difficult. Which means it’s a good time to remember that not all chestnuts are what they seem: Some, as Power found out, are horse chestnuts — similar in appearance and much more common, but inedible.

“They’re more than not edible,” says Mark Mead, senior urban forester for Seattle Parks and Recreation. “They’re poisonous.”

Still, unless you down a lot of horse chestnuts, they’re more likely to make you ill than kill you. Horse-chestnut poisoning is rarely fatal, according to the Web site of Canada’s Nova Scotia Museum, though effects can include vomiting, loss of coordination, stupor and occasionally paralysis.

Of the 418,000 accidental toxic-substance exposure calls received by Washington Poison Control from 2000-05, nut cases (horse chestnuts and buckeyes, which are related) accounted for barely 85. Most involved “minimal toxicity” and required no follow-up; two people reported minor effects.

The problem: Horse-chestnut trees are far more common than chestnut trees — for instance, lining the 17th Avenue boulevard near the University of Washington and the Carl S. English Jr. Garden in Ballard. Actual chestnut trees are harder to find, but highly sought-after: On one Queen Anne street featuring a number of them, residents annually clash with harvesters encroaching into yards to snatch the nuts as soon as they fall.

A home-and-garden information center operated by Clemson University Extension distinguishes good nut from bad nut (http://hgic.clemson.edu/factsheets/HGIC3270.htm).

Chestnuts are like woodsy sea urchins, sporting very prickly burrs with one to several nuts inside. Horse chestnuts are less prickly, more easily handled (and thus, more sinister).

Chestnuts have long, narrow leaves; horse chestnuts have big, compound ones composed of five to nine leaflets sharing a common stem.

Another difference: Chestnuts are starchy (and edible). Horse chestnuts taste horribly bitter. In a word: inedible.

Horse chestnuts, Mead adds, pretty much give themselves away with their nasty scent. And unlike edible chestnuts, their covers don’t pop off easily, which makes them, literally, a tougher nut to crack.

“Be very careful about what you’re picking up out there,” he says. “Which is true for anything.”